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"The “GeoCadastre”/ESRI “Survey Analyst” desktop Survey Data Model: Case study on business efficiencies and the role for surveyors"
IAN HARPER
GEODATA AUSTRALIA PTY LTD
Newcastle, NSW, Australia
Abstract
The paper will background how the new survey based cadastral management software integrates survey measurements and survey control to build a survey data model producing spatial quality related directly to the quality of survey information. (ie 20-40mm in areas of modern survey data).
Case studies where the process has been used to build and maintain survey accurate GIS cadastral models include; Northern Territory - A survey accurate Cadastral database has allowed Legislation to be enacted to create “Legal” Title Coordinates.
Hunter Water Corporation - A major infrastructure provider that has maintained a survey accurate cadastral database across 5 Local Government Areas for 10 years. Gloucester Shire Council - A rural Council located in mountainous terrain with areas of old Title plans with limited or no survey information and a Digitised Cadastral Database with poor spatial quality. A survey data model now allows areas easily upgraded as need and budgets allow. 10km urban rail corridor – A desktop survey data model of over 4000 parcels generated a corridor boundary with accuracies of <100mm to begin planning and design. Maintaining and improving the model will result in a future asset management system of the highest spatial quality.
Survey Analyst allows other GIS ‘feature’ datasets to be adjusted to maintain their “Associativity” with an upgraded cadastre.
Aspects of the difficulty in quantifying the business case for an accurate GIS cadastral database outside the GIS environment are discussed, as is the role a surveyor should play in creating the optimal GIS cadastral model.
INTRODUCTION
The cadastre is the foundation layer of most spatial databases as the ownership and the spatial extent of that ownership determines the outcomes achievable on that property. In the real world, ownership is accurately defined by surveyors placing visible features on the ground and providing records of their survey to the title registering authority. In Australia, surveyors are legislated to reach a certain professional standard to undertake that task and also accept the liabilities associated with the spatial component of title creation.
In the past, that same level of precise survey outcome has not been achievable in GIS cadastral databases due to software and hardware limitations. The result was that Surveyors have not embraced GIS because their precision levels were not sustainable in the GIS environment. Technology has now overcome the technical limitations but the continued development of GPS has also set a new standard in accessibility for accurate spatial definition. The real issue is that the legal cadastre is defined by historical survey records of varying spatial quality that do not easily translate to a geodetic spatial reference frame because monuments found on the ground have a higher legal weighting than any written or electronic record in defining the spatial location of a cadastral boundary. This is one of many rules in the survey process of cadastral boundary definition.
These rules are followed by the software process developed in Australia over the last 15 years by experienced land surveyor and lecturer Dr Michael Elfick and Systems Analyst Michael Fletcher and recently adopted by ESRI Survey Analyst - Cadastral Editor. The process facilitates the transition from the historical measurement based survey systems defining the cadastre to the incorporation of modern position based survey (GPS) systems to define the spatial location. This transition is achieved by the construction of a mesh of new and old survey measurement geometry, creating a SURVEY DATA MODEL (SDM)) as the platform to create and efficiently manage an accurate geodetic cadastral database. The process replicates workflows adopted by surveyors to define cadastral boundaries.
If all the available survey information from those historical and current records is used to create the database, the outcome is the most accurate desktop representation of the legal cadastre. With modern urban cadastral plans, the spatial quality of the model would be expected to be 20- 30mm.
Another rule adopted by the process is that when title measurements are adjusted to create a seamless fabric in the cadastral database, it is imperative that the measurements shown on the title diagram are accessed as the only dimension attribute of that title, even though the model dimension varies. This is an important legal “rule” for surveyors
SURVEY DATA MODEL (SDM) CREATION
STAGE 1 – DATA ENTRY
The SDM can be built to satisfy three business cases:
1. Manual data entry from existing survey plans
Record plans of varying survey quality (usually relative to age) are currently used by surveyors to define the legal cadastre. They identify legal and cadastral attributes (Parcel number, plan number, areas, dimensions, easement locations etc.) and they reflect the previous surveyor’s decision on the location of title boundaries on the ground. They also show extra survey information to support their decision and provide the registering authority with the evidence to guarantee that title. Including this extra information in the database adjustment provides more data, redundancies for checking, brings the model outcome closer to the surveyor’s spatial interpretation and allows the setting of survey rules for the model (maintaining road widths etc).
See Diagram A.
Diagram A – Various types of survey data entered
2. Importing of cadastre from electronic survey geometry databases
The cadastral fabric can be built or amended using electronic data from coordinate geometry software where surveyor’s measurements, geodetic survey control data and computations provide an accurate geodetic spatial location for their boundary definition. This is an efficient way of importing survey measurement data of the highest spatial precision, providing the source software identifies cadastral and property attribute details (usually in XML format) of plan, parcel, surveyor, geodetic control etc.
This method should allow the incorporation of at least the last 10 years of many surveyor’s electronic coordinate database, providing a significant resource of quality data.
3. Migration of existing cadastral databases
Most existing cadastral databases have been created as shape files by digitizing historical cadastral record base plans. These shape files provide parcels with property attributes including spatial referencing by coordinates which can be inversed to provide approximate fabric parcel dimensions. This is a rapid means to create an SDM with cadastral attributes however the data has no relation to existing survey/Title measurements and the curve geometry created is ‘best approximation’.
The benefit of this process is that it sets the framework for efficient spatial upgrading with new survey data.
STAGE 2 - PARCEL JOINING
Once the parcel dimensions and other survey measurements are entered from the survey title plans, the parcels are selectively joined to the SDM to force the outcome of a continuous fabric without overlaps & gaps. The process provides the greatest rigor in the checking of the data entry and reports on the quality of the ‘fit’ of the new data into the existing model. If a quality cadastral model exists, the method becomes a tool for checking the integrity of new survey data being added. The NSW Land Titles Office (LTO) is undertaking a pilot study for the checking of new survey plans as part of the process of electronic lodgement. The efficiencies for the LTO are the rapid reporting on the precision of the fit of the parcel and the adjoining survey information into the existing model. It can verify that the new survey data is at an acceptable standard and no further manual mathematical checking of the plan is required. This process can be achieved using less experienced plan checking staff, freeing up senior staff. Data imported by methods (2) & (3) is joined as groups of parcels and does not follow the same level of rigor.
STAGE 3 - THE ADJUSTMENT
The current and historical measurement geometry is adjusted in the model using a least squares adjustment. The adjustment also allows geodetic survey control marks in the model to be nominated as ‘inactive’ so new coordinates for that point are computed by the model. This provides independent verification when checked against the true coordinates. A detailed report is produced after every adjustment showing model displacements and comparisons between the adjusted model dimension and the original measurement dimension for every line. This provides an excellent troubleshooting tool for incorrect or poor data.
THE SURVEY DATA MODEL – Review of Methods
The SDM provides opportunities for varied means of cadastral database creation. The full process beginning with manual data entry involves higher costs initially but significant long term benefits are achieved. Data is checked at each stage, as it is entered, joined and adjusted and follows the highest level of rigor in survey workflows. Once the initial model is created, entering new data and upgrading the spatial quality of the cadastre is a very efficient process.
Importing of electronic survey data and migration of other databases will begin the process but upgrading of the database will not be as efficient.
CASE STUDIES – PROJECTS UTILISING MANUAL DATA ENTRY
Northern Territory
An SDM has been completed for the several major urban areas where most of the Northern Territory population reside. A similar database model is being built for the remote areas of the Territory cadastre which are defined by large Pastoral Leases and Aboriginal Lands. Pastoral Leases are already defined by Latitude & Longitude (ie Geodetic references) so the move to the position based GPS system and its efficiencies over conventional survey is a natural progression in jurisdictions outside urban areas.
That progression has seen Legislation for legal coordinates for Title boundary definition in proclaimed areas enacted in 2004.
The challenge being faced in the remote areas by the NT Lands Department is incorporating the survey records of the extensive ground survey traverses done over many years which previously defined those boundaries. Unfortunately, it is not simple as nominating coordinates to the 4 corners of the Pastoral Leases because legally, the pegged line is the boundary.
Hunter Water Corporation
The Hunter Water Corporation services a population of 500,000 over 5,000 sq km and has maintained a survey accurate database of assets and the cadastre for nearly 30 years. This was initially done using hand calculations.
Since 2000 our SDM process has been used by HWC to build and maintain an accurate database across the 210,000 properties serviced in 5 Local Government Areas in the Hunter Valley of NSW.
The maximum tolerance required for the database was originally based on minimising the area of uncertainty when the HWC is digging to locate an asset (half the width of a backhoe–300mm). The spatial quality is now considerably less than this.
The database is kept completely up to date by one person and the whole of the Corporation’s database is updated weekly.
Gloucester Shire Council
The Gloucester Local Government Area is a rural Council generally located in hilly/mountainous terrain with a total population is over 4,900 with Gloucester Township containing over half (2600).
The Council has limited professional resources with a total of 20 administration staff, including 1 GIS operator and corresponding budget limitations. Council was aware of the poor quality of the existing Digital Cadastral DataBase and its detrimental effect on an operational GIS. An SDM was created for the Gloucester LGA so that Council will have a framework to build a survey accurate GIS over time. They also needed to determine the extent of discrepancies between the DCDB and the numeric cadastral database A cadastre consisting of 4,264 historical & current parcels were captured and converted into a seamless parcel fabric. Many plans were old and had limited survey information. Discrepancies over 100 metres were found between the existing Digital Cadastral DataBase and the numerical cadastre created.
Plans of any development work (Subdivisions, Building or infrastructure) now undertaken in the LGA are lodged with Council and are required to be spatially accurate (endorsed by Registered Surveyor) to ensure an efficient transition to the GIS.
INFRASTRUCTURE PROJECT – URBAN RAIL UPGRADE - CASE STUDY AND OUTCOMES FOR ASSET MANAGEMENT.
The project involved the upgrade of 10km of an existing single line that serviced a historical rural area that has been identified as a major growth centre for Sydney’s future and was undertaken by the NSW Government authority – the Transport Infrastructure Development Corporation (TIDC).
To commence the planning and design stage, the project needed a survey accurate cadastral model of the route and it was also preferred for political reasons that this was done initially with a minimum of survey field work.
As a ‘big picture’ government infrastructure developer TIDC had a vision that at the completion of their management of the construction stage of the project, they would hand on to the railway operations department of government, a valuable database of the highest spatial quality for ongoing asset management.
More than 4,000 parcels were entered to provide a rigorous model for the adjustment. (See Diagram B) In the model area, more than 130 Coordinated Survey Control Marks with survey connections to the cadastre were found in the NSW Lands Department Survey Control database. The coordinates of approximately 90 of those marks were of the highest accuracy and considered suitable to be used as accurate control for the adjustment.
Following completion of the desktop model, two days of field work was undertaken in several areas where properties were defined by older survey plans and required verification or more definition. Cadastral survey marks including pegs and reference marks, were located and coordinated by Global Positioning Systems (GPS).
On one field day, the model was taken into the field with GPS and the desktop model coordinates allowed the surveyors to navigate accurately (0.05 – 0.5 meters) to marks on the ground or where buried marks were located. In many cases the model quickly allowed recognition that survey marks had been destroyed by cables or other works.
This type of project may otherwise require 4 weeks or more field survey to create the cadastral model, which highlights the efficiencies in the reduction of a high cost component of the planning and design stage.
Diagram B - TIDC survey data model
The survey connectivity and rigor of the desktop data allowed the model to be created and adjusted needing only one extra field control mark. In the final model, sixteen control points were held fixed with the remainder assigned a ‘not active’ status. The inactive control points reporting the following error range:
The spatial accuracy of the final TIDC model is in the order of 30mm – 100mm in urban areas where reasonable survey information is available and 100mm-200mm in rural or other areas of older survey plans where there was limited survey information. The survey pegs and marks coordinated in the field confirmed these results.
The business outcomes from the project include a reduction in survey costs at the start of the project as the amount of survey control required for the project is significantly reduced and provides the basis for efficient upgrading as the project develops. The project now has a survey accurate cadastral database with property attributes to underpin the project GIS database for ongoing design, construction & asset management.
A NEW RELATIONSHIP BETWEEN SURVEY AND GIS
Survey accuracy in a cadastral database encourages a mutually beneficial environment for both surveyors and GIS professionals.
In local government and service utilities, the surveyors are now able to work more closely with the GIS staff and are more interested in collecting accurate information for the GIS. The GIS can be useful to the surveyor with additional information (aerial photography) that may assist in locating survey marks or other assets they are seeking in the field. Working as a team, the operations and data management requirements of organizations are better serviced through a survey accurate asset management system.
OUTCOMES FOR GIS PROFESSIONALS
Increased spatial accuracy of asset databases means considerable efficiencies with data migration. Future database management can rely on accurate spatial attributes of the data to solely represent position without the need to link assets to the cadastre or other features so that it ‘looks right’.
Where data has no accurate coordinate attributes, it can now be linked to the accurate cadastre with the satisfaction that its spatial location is correct in a geodetic framework. This initial spatial accuracy is further enhanced by the management tools within the ArcGIS environment that retain that relationship link as the cadastre precision is increased in the future. The SDM is a survey process for GIS cadastral management which will benefit from the involvement of surveyors.
OUTCOMES FOR SURVEYORS
The SDM process provides a new level of survey data management for surveyors. Surveyor’s personal historical records contain elements of survey information that may be of benefit to them in the future. For years, these file records have been retained on paper as their personal survey database and recycled when working on or adjacent to those old jobs. The surveyor’s public database consists of the survey plans defining cadastral title boundaries done by other surveyors and stored in the title registry.
Since the 1980’s Geodetic referencing of surveys was required in NSW, but the majority of titles were still referenced by local survey monuments such as pegs, buried pipes or concrete blocks. Surveyors found these marks to orientate their surveys and stored references to them in their records. Some of this data would be used in the preparation of subdivision plans and will then be available on public record.
The advent of computers and coordinate geometry software then allowed them to electronically store their personal survey boundary definitions, firstly on a local datum and more recently on a standard geodetic one.
Using the existing plans and their own measurements, a surveyor then used their intuition & experience to make decisions on boundary location in their coordinate geometry software. The SDM process follows those intuitive survey rules in the creation of the cadastral fabric. Surveyors now build an SDM for all jobs (large and small) so problems in survey plans can be found prior to field work and field work can be planned more efficiently. The SDM is also used in the field allowing the surveyor to accurately search for cadastral survey marks. When a mark is found, new coordinates are fixed for the mark and the model is readjusted. The increase in the precision of the model allows other marks to be found more easily.
THE BUSINESS CASE
The benefits of an accurate survey data model are efficient operations and no problems caused by a cadastral layer of unknown spatial quality.
Currently there is no appreciation of the real economies of the issues and no true accounting of the real cost of inefficiencies or problems. You cannot quantify the true value of such an asset for the future. People who have had to deal with spatially poor GIS databases in the past are the only ones who truly recognise the value.
Spatially accurate data is easily transported internally & externally and risk management issues and potential liabilities are reduced.
CONCLUSION – THE FUTURE FOR SPATIAL DATA
The NSW Lands Department are introducing GPS Continually Operating Reference Stations (CORS) that will be accessible across the state and will provide the surveyor with centimeter geodetic accuracy for all their GPS measurements in the future.
Higher precision basic GPS systems are also in more general use so it is important that spatial databases are able to meet that challenge.
The Survey Data Model built from survey measurements is the best way to efficiently create an accurate cadastral layer as is the foundation for spatial databases and Land Title management. As custodians of the cadastre it is important the surveyor has a role in the management of the cadastral layer and that in the future the cadastral layer has survey merit and is not a ‘pictorial’ layer.
IAN HARPER
GEODATA AUSTRALIA PTY LTD
Newcastle, NSW, Australia
Abstract
The paper will background how the new survey based cadastral management software integrates survey measurements and survey control to build a survey data model producing spatial quality related directly to the quality of survey information. (ie 20-40mm in areas of modern survey data).
Case studies where the process has been used to build and maintain survey accurate GIS cadastral models include; Northern Territory - A survey accurate Cadastral database has allowed Legislation to be enacted to create “Legal” Title Coordinates.
Hunter Water Corporation - A major infrastructure provider that has maintained a survey accurate cadastral database across 5 Local Government Areas for 10 years. Gloucester Shire Council - A rural Council located in mountainous terrain with areas of old Title plans with limited or no survey information and a Digitised Cadastral Database with poor spatial quality. A survey data model now allows areas easily upgraded as need and budgets allow. 10km urban rail corridor – A desktop survey data model of over 4000 parcels generated a corridor boundary with accuracies of <100mm to begin planning and design. Maintaining and improving the model will result in a future asset management system of the highest spatial quality.
Survey Analyst allows other GIS ‘feature’ datasets to be adjusted to maintain their “Associativity” with an upgraded cadastre.
Aspects of the difficulty in quantifying the business case for an accurate GIS cadastral database outside the GIS environment are discussed, as is the role a surveyor should play in creating the optimal GIS cadastral model.
INTRODUCTION
The cadastre is the foundation layer of most spatial databases as the ownership and the spatial extent of that ownership determines the outcomes achievable on that property. In the real world, ownership is accurately defined by surveyors placing visible features on the ground and providing records of their survey to the title registering authority. In Australia, surveyors are legislated to reach a certain professional standard to undertake that task and also accept the liabilities associated with the spatial component of title creation.
In the past, that same level of precise survey outcome has not been achievable in GIS cadastral databases due to software and hardware limitations. The result was that Surveyors have not embraced GIS because their precision levels were not sustainable in the GIS environment. Technology has now overcome the technical limitations but the continued development of GPS has also set a new standard in accessibility for accurate spatial definition. The real issue is that the legal cadastre is defined by historical survey records of varying spatial quality that do not easily translate to a geodetic spatial reference frame because monuments found on the ground have a higher legal weighting than any written or electronic record in defining the spatial location of a cadastral boundary. This is one of many rules in the survey process of cadastral boundary definition.
These rules are followed by the software process developed in Australia over the last 15 years by experienced land surveyor and lecturer Dr Michael Elfick and Systems Analyst Michael Fletcher and recently adopted by ESRI Survey Analyst - Cadastral Editor. The process facilitates the transition from the historical measurement based survey systems defining the cadastre to the incorporation of modern position based survey (GPS) systems to define the spatial location. This transition is achieved by the construction of a mesh of new and old survey measurement geometry, creating a SURVEY DATA MODEL (SDM)) as the platform to create and efficiently manage an accurate geodetic cadastral database. The process replicates workflows adopted by surveyors to define cadastral boundaries.
If all the available survey information from those historical and current records is used to create the database, the outcome is the most accurate desktop representation of the legal cadastre. With modern urban cadastral plans, the spatial quality of the model would be expected to be 20- 30mm.
Another rule adopted by the process is that when title measurements are adjusted to create a seamless fabric in the cadastral database, it is imperative that the measurements shown on the title diagram are accessed as the only dimension attribute of that title, even though the model dimension varies. This is an important legal “rule” for surveyors
SURVEY DATA MODEL (SDM) CREATION
STAGE 1 – DATA ENTRY
The SDM can be built to satisfy three business cases:
1. Manual data entry from existing survey plans
Record plans of varying survey quality (usually relative to age) are currently used by surveyors to define the legal cadastre. They identify legal and cadastral attributes (Parcel number, plan number, areas, dimensions, easement locations etc.) and they reflect the previous surveyor’s decision on the location of title boundaries on the ground. They also show extra survey information to support their decision and provide the registering authority with the evidence to guarantee that title. Including this extra information in the database adjustment provides more data, redundancies for checking, brings the model outcome closer to the surveyor’s spatial interpretation and allows the setting of survey rules for the model (maintaining road widths etc).
See Diagram A.
Diagram A – Various types of survey data entered
2. Importing of cadastre from electronic survey geometry databases
The cadastral fabric can be built or amended using electronic data from coordinate geometry software where surveyor’s measurements, geodetic survey control data and computations provide an accurate geodetic spatial location for their boundary definition. This is an efficient way of importing survey measurement data of the highest spatial precision, providing the source software identifies cadastral and property attribute details (usually in XML format) of plan, parcel, surveyor, geodetic control etc.
This method should allow the incorporation of at least the last 10 years of many surveyor’s electronic coordinate database, providing a significant resource of quality data.
3. Migration of existing cadastral databases
Most existing cadastral databases have been created as shape files by digitizing historical cadastral record base plans. These shape files provide parcels with property attributes including spatial referencing by coordinates which can be inversed to provide approximate fabric parcel dimensions. This is a rapid means to create an SDM with cadastral attributes however the data has no relation to existing survey/Title measurements and the curve geometry created is ‘best approximation’.
The benefit of this process is that it sets the framework for efficient spatial upgrading with new survey data.
STAGE 2 - PARCEL JOINING
Once the parcel dimensions and other survey measurements are entered from the survey title plans, the parcels are selectively joined to the SDM to force the outcome of a continuous fabric without overlaps & gaps. The process provides the greatest rigor in the checking of the data entry and reports on the quality of the ‘fit’ of the new data into the existing model. If a quality cadastral model exists, the method becomes a tool for checking the integrity of new survey data being added. The NSW Land Titles Office (LTO) is undertaking a pilot study for the checking of new survey plans as part of the process of electronic lodgement. The efficiencies for the LTO are the rapid reporting on the precision of the fit of the parcel and the adjoining survey information into the existing model. It can verify that the new survey data is at an acceptable standard and no further manual mathematical checking of the plan is required. This process can be achieved using less experienced plan checking staff, freeing up senior staff. Data imported by methods (2) & (3) is joined as groups of parcels and does not follow the same level of rigor.
STAGE 3 - THE ADJUSTMENT
The current and historical measurement geometry is adjusted in the model using a least squares adjustment. The adjustment also allows geodetic survey control marks in the model to be nominated as ‘inactive’ so new coordinates for that point are computed by the model. This provides independent verification when checked against the true coordinates. A detailed report is produced after every adjustment showing model displacements and comparisons between the adjusted model dimension and the original measurement dimension for every line. This provides an excellent troubleshooting tool for incorrect or poor data.
THE SURVEY DATA MODEL – Review of Methods
The SDM provides opportunities for varied means of cadastral database creation. The full process beginning with manual data entry involves higher costs initially but significant long term benefits are achieved. Data is checked at each stage, as it is entered, joined and adjusted and follows the highest level of rigor in survey workflows. Once the initial model is created, entering new data and upgrading the spatial quality of the cadastre is a very efficient process.
Importing of electronic survey data and migration of other databases will begin the process but upgrading of the database will not be as efficient.
CASE STUDIES – PROJECTS UTILISING MANUAL DATA ENTRY
Northern Territory
An SDM has been completed for the several major urban areas where most of the Northern Territory population reside. A similar database model is being built for the remote areas of the Territory cadastre which are defined by large Pastoral Leases and Aboriginal Lands. Pastoral Leases are already defined by Latitude & Longitude (ie Geodetic references) so the move to the position based GPS system and its efficiencies over conventional survey is a natural progression in jurisdictions outside urban areas.
That progression has seen Legislation for legal coordinates for Title boundary definition in proclaimed areas enacted in 2004.
The challenge being faced in the remote areas by the NT Lands Department is incorporating the survey records of the extensive ground survey traverses done over many years which previously defined those boundaries. Unfortunately, it is not simple as nominating coordinates to the 4 corners of the Pastoral Leases because legally, the pegged line is the boundary.
Hunter Water Corporation
The Hunter Water Corporation services a population of 500,000 over 5,000 sq km and has maintained a survey accurate database of assets and the cadastre for nearly 30 years. This was initially done using hand calculations.
Since 2000 our SDM process has been used by HWC to build and maintain an accurate database across the 210,000 properties serviced in 5 Local Government Areas in the Hunter Valley of NSW.
The maximum tolerance required for the database was originally based on minimising the area of uncertainty when the HWC is digging to locate an asset (half the width of a backhoe–300mm). The spatial quality is now considerably less than this.
The database is kept completely up to date by one person and the whole of the Corporation’s database is updated weekly.
Gloucester Shire Council
The Gloucester Local Government Area is a rural Council generally located in hilly/mountainous terrain with a total population is over 4,900 with Gloucester Township containing over half (2600).
The Council has limited professional resources with a total of 20 administration staff, including 1 GIS operator and corresponding budget limitations. Council was aware of the poor quality of the existing Digital Cadastral DataBase and its detrimental effect on an operational GIS. An SDM was created for the Gloucester LGA so that Council will have a framework to build a survey accurate GIS over time. They also needed to determine the extent of discrepancies between the DCDB and the numeric cadastral database A cadastre consisting of 4,264 historical & current parcels were captured and converted into a seamless parcel fabric. Many plans were old and had limited survey information. Discrepancies over 100 metres were found between the existing Digital Cadastral DataBase and the numerical cadastre created.
Plans of any development work (Subdivisions, Building or infrastructure) now undertaken in the LGA are lodged with Council and are required to be spatially accurate (endorsed by Registered Surveyor) to ensure an efficient transition to the GIS.
INFRASTRUCTURE PROJECT – URBAN RAIL UPGRADE - CASE STUDY AND OUTCOMES FOR ASSET MANAGEMENT.
The project involved the upgrade of 10km of an existing single line that serviced a historical rural area that has been identified as a major growth centre for Sydney’s future and was undertaken by the NSW Government authority – the Transport Infrastructure Development Corporation (TIDC).
To commence the planning and design stage, the project needed a survey accurate cadastral model of the route and it was also preferred for political reasons that this was done initially with a minimum of survey field work.
As a ‘big picture’ government infrastructure developer TIDC had a vision that at the completion of their management of the construction stage of the project, they would hand on to the railway operations department of government, a valuable database of the highest spatial quality for ongoing asset management.
More than 4,000 parcels were entered to provide a rigorous model for the adjustment. (See Diagram B) In the model area, more than 130 Coordinated Survey Control Marks with survey connections to the cadastre were found in the NSW Lands Department Survey Control database. The coordinates of approximately 90 of those marks were of the highest accuracy and considered suitable to be used as accurate control for the adjustment.
Following completion of the desktop model, two days of field work was undertaken in several areas where properties were defined by older survey plans and required verification or more definition. Cadastral survey marks including pegs and reference marks, were located and coordinated by Global Positioning Systems (GPS).
On one field day, the model was taken into the field with GPS and the desktop model coordinates allowed the surveyors to navigate accurately (0.05 – 0.5 meters) to marks on the ground or where buried marks were located. In many cases the model quickly allowed recognition that survey marks had been destroyed by cables or other works.
This type of project may otherwise require 4 weeks or more field survey to create the cadastral model, which highlights the efficiencies in the reduction of a high cost component of the planning and design stage.
Diagram B - TIDC survey data model
The survey connectivity and rigor of the desktop data allowed the model to be created and adjusted needing only one extra field control mark. In the final model, sixteen control points were held fixed with the remainder assigned a ‘not active’ status. The inactive control points reporting the following error range:
The spatial accuracy of the final TIDC model is in the order of 30mm – 100mm in urban areas where reasonable survey information is available and 100mm-200mm in rural or other areas of older survey plans where there was limited survey information. The survey pegs and marks coordinated in the field confirmed these results.
The business outcomes from the project include a reduction in survey costs at the start of the project as the amount of survey control required for the project is significantly reduced and provides the basis for efficient upgrading as the project develops. The project now has a survey accurate cadastral database with property attributes to underpin the project GIS database for ongoing design, construction & asset management.
A NEW RELATIONSHIP BETWEEN SURVEY AND GIS
Survey accuracy in a cadastral database encourages a mutually beneficial environment for both surveyors and GIS professionals.
In local government and service utilities, the surveyors are now able to work more closely with the GIS staff and are more interested in collecting accurate information for the GIS. The GIS can be useful to the surveyor with additional information (aerial photography) that may assist in locating survey marks or other assets they are seeking in the field. Working as a team, the operations and data management requirements of organizations are better serviced through a survey accurate asset management system.
OUTCOMES FOR GIS PROFESSIONALS
Increased spatial accuracy of asset databases means considerable efficiencies with data migration. Future database management can rely on accurate spatial attributes of the data to solely represent position without the need to link assets to the cadastre or other features so that it ‘looks right’.
Where data has no accurate coordinate attributes, it can now be linked to the accurate cadastre with the satisfaction that its spatial location is correct in a geodetic framework. This initial spatial accuracy is further enhanced by the management tools within the ArcGIS environment that retain that relationship link as the cadastre precision is increased in the future. The SDM is a survey process for GIS cadastral management which will benefit from the involvement of surveyors.
OUTCOMES FOR SURVEYORS
The SDM process provides a new level of survey data management for surveyors. Surveyor’s personal historical records contain elements of survey information that may be of benefit to them in the future. For years, these file records have been retained on paper as their personal survey database and recycled when working on or adjacent to those old jobs. The surveyor’s public database consists of the survey plans defining cadastral title boundaries done by other surveyors and stored in the title registry.
Since the 1980’s Geodetic referencing of surveys was required in NSW, but the majority of titles were still referenced by local survey monuments such as pegs, buried pipes or concrete blocks. Surveyors found these marks to orientate their surveys and stored references to them in their records. Some of this data would be used in the preparation of subdivision plans and will then be available on public record.
The advent of computers and coordinate geometry software then allowed them to electronically store their personal survey boundary definitions, firstly on a local datum and more recently on a standard geodetic one.
Using the existing plans and their own measurements, a surveyor then used their intuition & experience to make decisions on boundary location in their coordinate geometry software. The SDM process follows those intuitive survey rules in the creation of the cadastral fabric. Surveyors now build an SDM for all jobs (large and small) so problems in survey plans can be found prior to field work and field work can be planned more efficiently. The SDM is also used in the field allowing the surveyor to accurately search for cadastral survey marks. When a mark is found, new coordinates are fixed for the mark and the model is readjusted. The increase in the precision of the model allows other marks to be found more easily.
THE BUSINESS CASE
The benefits of an accurate survey data model are efficient operations and no problems caused by a cadastral layer of unknown spatial quality.
Currently there is no appreciation of the real economies of the issues and no true accounting of the real cost of inefficiencies or problems. You cannot quantify the true value of such an asset for the future. People who have had to deal with spatially poor GIS databases in the past are the only ones who truly recognise the value.
Spatially accurate data is easily transported internally & externally and risk management issues and potential liabilities are reduced.
CONCLUSION – THE FUTURE FOR SPATIAL DATA
The NSW Lands Department are introducing GPS Continually Operating Reference Stations (CORS) that will be accessible across the state and will provide the surveyor with centimeter geodetic accuracy for all their GPS measurements in the future.
Higher precision basic GPS systems are also in more general use so it is important that spatial databases are able to meet that challenge.
The Survey Data Model built from survey measurements is the best way to efficiently create an accurate cadastral layer as is the foundation for spatial databases and Land Title management. As custodians of the cadastre it is important the surveyor has a role in the management of the cadastral layer and that in the future the cadastral layer has survey merit and is not a ‘pictorial’ layer.