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Quality control for land base and facilities conversion
Mohammad Tariq
Program Manager (GIS), Boston Water and Sewer Commission
425 Summer Street, Boston, MA 02210
David Koehler
Sr. Research Analyst,Pkmgraphics, Inc.
1300 Spring Street, Silver Spring, MD 20910
Mohammad Tariq
Program Manager (GIS), Boston Water and Sewer Commission
425 Summer Street, Boston, MA 02210
David Koehler
Sr. Research Analyst,Pkmgraphics, Inc.
1300 Spring Street, Silver Spring, MD 20910
Abstract
One of the key factors in timely and successfi,d implementation of an AM/FM/GIS is the establishment of quality control procedures for reviewing and accepting products from conversion contractors. The Boston Water and Sewer Commission implemented uniform quality control (QC ) procedures for inspection of hard copy and digital products to ensure confidence in the accuracy of the land base and facilities GIS databases being developed. The hard copy and digital data are checked to confirm content and positional accuracy of graphic features, adherence to the database design, correctness of attribute data, annotation, topology and overall consistency and completeness of the databases.
Introduction
The Commission is responsible for providing water and sewer and storm drainage services in the City of Boston. The City encompasses approximately 45 square miles of area and according to the 1990 US census has a residential population of 574,283, plus an additional daytime population of 480,000. The Commission owns and maintains approximately 1,340 miles of sewers, including 535 miles of sanitary sewers, 490 miles of storm drains, and 315 miles of combined sewers, and a number of other facilities, including pumping stations, tidegates and regulators. All wastewater generated in the city is transported to the Massachusetts Water Resources Authority (MWRA) treatment facilities located at Deer Island in Boston and Nut Island in Quincy. The Commission also owns and maintains approximately 1,182 miles of water mains. Water for the City of Boston is purchased from the MWRA at an average of about 90 million gallons per day. There are currently 85,500 customer accounts.
The majority of the Commission’s maps and data regarding water and sewer facilities are in paper format. Existing water and sewer-related information is maintained on 100’and 50’ scale maps. These maps, drawings and related data are updated and revised manually.
The Commission’s major objectives in establishing an AM/FM/GIS are to:
- Develop an efficient means of maintaining up-to-date water and sewer system maps and data bases.
- Develop and maintain a single, centralized source of facilities information which is easily accessible to all departments.
- Develop a means of sorting, processing, manipulating and storing facilities information.
Database Development Activities
Land Base Mapping
new land base is being created from aerial photography taken during the spring of 1995. The land base data includes development of 1“= 100’scale digital planimetric and topographic data as well as digital orthophotography. The production of land base data required the acquisition of color aerial photography at 1”= 600’ scale taken from an altitude of 3,600 feet, and establishment of horizontal and vertical photo control and aerotriangulation.
The planimetric features such as transportation, hydrography, buildings, wetlands and other land features have an accuracy of +/- 2’. These land base features are stereocompiled from the aerial photography described above. The digital orthophotos have a pixel resolution of 1 foot. The topographic data includes 2’ contours and spot elevations derived from a Digital Terrain Model (DTM).
Facilities Conversion
The Commission’s existing 1“= 100’scale water and sewer maps are used as the primary source for conversion of facilities data to digital format. The facilities data is registered to the new land base map developed from the aerial photography, as described above. The facilities data includes graphic data as well as attribute data stored in an Oracle database.
Delivery of Products
The city is divided into 12 areas for the delivery of data. The map sheets associated with these areas are called delivery groups. The delivery groups generally contain 23 map sheets. Deliveries occur on a monthly basis. The planimetric, topographic, and digital orthophoto data is being completed prior to the start of the facilities conversion effort. The same delivery groups apply for both the land base data deliveries and the facilities data deliveries.
Acceptance criteria of Delivered Products
A QC review is performed by the Commission for each delivery of products by the contractor. After QC review of the check plots, confirmation plots or digital data, the Commission determines the status of the product according to the following list: All the products which have systematic errors that impede the review are rejected. The cause of rejections are typically:
- A class of features is missing from plot
- Plot quality is poor
- Overall line quality is unacceptable
- An error, such as miscoding of features, is repeated more than 15 times
Corrections Required
The QC reviewers make comments for corrections during QC review. These comments maybe on check plots, confirmation plots, or digital data, depending on the stage of the review. In case of check or confirmation plots, the comments for corrections are placed directly on the plots. In the case of digital QC, comments are annotated on a digital GDS drawing which overlays the relevant digital drawing files. In response to these comments, the contractor is required to submit a confirmation plot or new digital data at the Commission’s discretion.
The Commission accepts the submittal of the product. This authorizes the contractor to submit digital data. If the acceptance is of digital data, then the product is filly accepted.
Accepted/BWSC Edit
The Commission determines that required corrections are minor enough to accept the submitted product, however any errors noted will be corrected by the Commission staff once the entire digital delivery group is accepted.
Quality contorl procedures
The QC process includes review of hard copy plots of land base and facilities data and subsequent reviews of digital data provided by the conversion contractors. An overview of the QC process is outlined in Figure 1 and described below. Hard copy review is completed first for a delivery group and digital review is completed after acceptance of hard copy plots.
Review of Hard COPYCheck plots
Hard copy review is primarily performed to verify feature content, identi~ missing features, review quality of linework, check annotation placement and content, and determine overall map quality and appearance. Digital orthophotos are checked for image clarity, contrast, distortion or any other defects which could impact the visual quality of the image. Check plots are used for the hard copy QC. The Contractor is required to submit check plots for each map sheet in the delivery group. There are check plots for each type of digital product:
- Digital orthophoto plot
- Planimetric features plot
- Planimetric and topographic features plot
- Water facilities plot
- Sewer facilities plot
1. Preliminary Review Upon receipt of check plots, the Commission reviews the plots to ensure that they are sufficiently legible and complete, and are plotted according to the acceptable standards using the required scale and sheet format. Once legibility has been determined, the check plots are logged into the GIS quality control status tracking application and assigned for review.
2. Digital Orthophoto Review The digital orthophoto plots are checked primarily for image clarity, contras$ image distortion or any defects that could impact the visual quality of the image, such as cloud shadows, misalignments, or dirt. Adjacent orthophoto plots are checked for uniformity of color representation, contrast, and clarity. If there are any problems with image quality, the digital orthophoto plot(s) are returned to the contractor with written documentation of the problems. The contractor is responsible for the correction of digital orthophotos and is required to submit another series of hard copy check plots for review. If any problems with the rectification of the orthophotos are evident, the entire delivery group is rejected.
3. Detailed Planimetric Data Review The orthophotos are used to check the planimetric data using a light table overlay where the planimetric plot is registered to the digital orthophoto to veri~ the general feature content. Precise registration is verified during the digital QC checks. When planimetric features on the photo image that have been designated in the database design are not captured, corrections are noted on the check plot. To streamline the feature checking procedure, the QC reviewer checks features on a block by block basis. Small check marks are placed next to each feature to keep track of areas on the check plot as they are examined. Street centerlines are checked for their continuity and to ensure that they are joined at intersections and represent a schematic geometric center of streets. Symbology, general appearance and quality of graphic features are reviewed, specifically smoothness of lines and absence of unnecessary spikes, jags, or wobbles. Finally, annotation is examined to ensure that features requiring annotation according to the database design have the correct character style and size. Annotation content is compared with a known source to ensure that features are labeled accurately. Street and place names are checked using sources such as existing 100’scale maps and the City of Bostons’s Street Index.
4. Detailed Topographic Data Review The topographic plots are examined for crossing contours, contours out of sequence, unusual spikes that protrude from contour lines, and correct Iinestyles for the various types of contour lines (e.g. index contours and depression contours). Areas that are checked carefhlly are large flat areas such as parking lots, or large building footprints. These are generally areas that have been leveled off during construction and should be represented as such by the contour lines. When the contour representation across an area is suspect, the representation can be checked by referring to the original aerial photos. By using a stereoscope to examine the stereo pair associated with the area in question, topographic representation on the check plot can be evaluated. Further evaluation can be accomplished by reviewing the DTM data. Plots of DTMs can also be requested, if necessary. Edits, which the contractor subsequently makes to the contours, should be reflected in the DTM data. Topographic annotation is also checked for index contours. For its placement, labels should be “stacked” at appropriate points, and they should not interfere with planimetric features. As with the planimetric plot, the QC reviewer examines the topographic check plot block by block to efficiently cover the entire map sheet and ensure that all features are checked.
5. Water and Sewer Facilities Data Review A light table overlay method is used to compare the water and sewer system check plots with the original source maps. As with the pkmimetric check plot, small check marks are placed next to each feature to keep track of the pipes and appurtenances that have been checked. The plots are checked to ensure that all features on the source maps are captured in the digital data, and the alignment of pipes and appurtenances are checked against the source maps. There is a significant amount of annotation on the facility maps and it must be captured correctly. The annotation check is done with the check plot and the source map side by side, and each annotation block is also marked with a small check as it is compared to the corresponding annotation on the source maps.
6. Designation of Check Plots The Commission determines the designation of each completed check plot in accordance with the four possible acceptance criteria described above. It is possible that an orthophoto can be rejected for aesthetic reasons and the planimetric and topographic features still be accepted for the same map. If either the planimetric or the topographic plot are rejected, this constitutes an overall rejection of the planimetric or topo data. Both pkmimetric and topo data must be accepted to designate the map sheet as accepted. As long as the digital orthophoto is adequate to support planimetric compilation, then the orthophoto can be rejected and the planimetric and topographic features can still be accepted. The complete transmittal back to the Contractor is prepared with the result and required action indicated for each map sheet in the delivery group.
Review of Hard Copy Confirmation Plots
The Contractor corrects all the errors indicated on the check plots and submits confirmation plots when requested to do so. A confirmation plot is sent to the Commission along with the original check plot so that QC reviewers can specifically verifj that the indicated errors have been corrected. As with the check plots, the confirmation plots are given a designation of one of the four acceptance categories described earlier. Confirmation plots are only rejected if corrections are not made as noted on the check plots. Confirmation plots are returned for corrections if the requested corrections are not made satisfactorily. The plot is accepted if all the indicated errors have been corrected. If it is determined that the contractor did not carry out the corrections to an acceptable level or new errors are introduced or new errors are present that were not in the original check plot, the confirmation plot is returned to the contractor for corrections.
Performing Digital QC
After the hard copy QC has been completed for an entire delivery group, digital QC is performed on the delivexy group. The purpose of digital QC is to verifi digital orthophoto tone and contrast, planimetric and facility feature coding errors, edgematching, correct topology, data structure, and compliance with the database design. Two applications (one for land base data and another for facilities data) were developed in GDS to check that all the features were captured according to the database design. Figure 2 shows an example of one of the GDS QC application menus. A description of the components of the two QC applications follows:
1. Digital Orthophoto ReviewBoth color and monochrome versions of the digital orthophotos are checked visually on the screen for tone and contrast. The edges are checked against the map sheet grid to ensure proper alignment and the planimetric features are checked for accurate registration. The orthophotos are also checked for image distortion and mosaicking with the adjacent orthophoto. The hardware zoom and pan fi.mctions are used to zoom in on ground features such as pavement or water edges to check for registration errors between the vector data and the digital orthophotos.
2. Specifications CheckAll the features which have coding errors are displayed and queried to determine the coding error. A plot of the features with wrong codes can be generated, if so desired. A report that lists the features that do not correspond to the database design in terms of coding, line style, or character style is created, and the features that do not conform are assigned error codes, such as ERO (objects) or ERI (items).
3. Predetermined DisplaysPredetermined feature displays are required for the more detailed feature checks to be performed. All features are drawn in white on the screen. Subsequent choices from feature selection sets will overlay the white background with colored line representations on a feature by feature basis. This function of the QC application allows the users to query any features that do not get drawn in response to the correct feature code, or features that do not get drawn at all. For example, if the user specifies that “wetlands” features to be drawn in blue on top of white planimetric features, and some “wetlands” remains white rather than turning blue, the user will recognize that those “wetlands” features have received incorrect codes. This differs from the land base specifications check since a feature code might be a valid code according to the database design, but the code is inappropriately assigned to the individual feature (e.g. the miscoded “wetlands” features are queried and it is discovered that they have been accidentally coded as “river”).
4. Data Structure and Topological Checks The QC applications provide selections to check for required topology in the data and to highlight any situations where the structure of the digital data is inappropriate. For instance by assigning a special linestyle to line features, such as pipes, small ticks can be created at every vertex to show where some vertices exist in the middle of a straight section of pipe or to illustrate sections where vertices need to be added.
Another function of the QC application allows the user to check the connectivity of lines. This is important for checking the water and sewer systems and street centerlines. Lines to be checked are displayed, then the user is prompted for two points along the network of lines. The program traces a line between the two points and beeps if no connecting path can be found. Another selection is to shade all topologically structured polygons, such as buildings and parking lots to ensure that these have been assigned topology as required.
5. Edit Calls The QC applications have fimctions designed to indicate errors on a GDS drawing (called an ERR drawing) that overlays the GIS data. The user is provided with a set of menu selections that provide tools to quickly indicate Wd describe errors on the ERR drawing. First the user must specify which 752?drawing is being QC’d in order to set a label which refers to that drawing, then the user can choose from an assortment of tools which indicates a feature or defines an area that needs to be corrected. Another fimction produces an error report listing all the features that have been assigned wrong codes. Both the error report and the ERR drawing are provided to the contractor for making corrections to the digital data.
Lessons Learned
- A significant investment of time must be expended in the quality control process. Time estimates
used for planning quality control activities are (per map sheet):
Digital Orthophoto Check Plot -30 minutes Planimetric Check Plot -90 minutes Topo Check Plot -30 minutes Water System Check Plot -180 minutes Sewer System Check Plot -180 minutes Planimetric, Topographic, and Digital Orthophoto Digital QC -90 minutes Water System Digital QC -120 minutes Sewer System Digital QC -120 minutes
- There area variety of options that an organization can consider when planning the logistics of
conducting quality control during a large data conversion project:
Contract out all quality control work
Complete in-house quality control
Split QC responsibility with a contractor
Contract out QC management, QC staff training, and QC application development
The choice depends on the amount of money that can be spent on such an endeavor and the flexibility an organization has in terms of hiring. The more QC there is conducted in-house the less expensive the QC will be, but there will be requirements for hiring a QC manager or assigning those duties to an existing employee. The QC duties will take the QC manager away from most other work until the period of data conversion is over (anywhere from 1 to 3 years or more). QC technicians will also need to be hired. It is suggested that there be significant in-house GIS expertise if complete in-house QC review is planned by an organization.
The other options are varying degrees of using contractors. If the organization feels it can provide technical staff, but needs expertise, contracting out QC management, training and application development can be effective. Splitting QC responsibility with a contractor is appropriate when an organization feels it can only commit portions of their staff members time. Finally contracting out all QC work, can be effective when an organization has restrictions on hiring and does not have the existing personnel to carry out the necessary steps.
- Development of a database design is extremely important and should be understood by both the QC
reviewers and the conversion contractor. An initial pilot project should be conducted that tests the
adequacy of the database design. The pilot project should result in a database design that has been
updated to reflect all changes necessary to accommodate unforeseen circumstances. Also, a formal
procedure should be developed for proposing and accepting changes to the database design during
the compilation and conversion process.
- A large data conversion project results in the generation of a great quantity of hard copy plots that need to be kept in an organized fashion. When planning for quality control, provisions must be made for storing plots in a manner that allows el%cient retrieval by delivery group and status. Often there will be check plot deliveries for a delivery group during the same time period that the contractor is submitting confirmation plots with accompanying check plots from a previous delivery group. It is important for the sake of efficiency to be able to store them all separately. Several methods for tracking quality control must be implemented. A digital quality control application that color codes map sheet tiles according to the acceptance status, scheduled delivery date, delivery group, and staff member assignment is extremely helpfid. This provides a quick way to generate graphic status reports. Other aspects of quality control tracking involve developing transmittal sheets, and a quality control log.
Data conversion is a complex task and requires careful planning and management. A comprehensive workpkm should be developed which outlines what features are to be captured, how they are to be captured and represented and coded, and what attributes are to be recorded. A pilot project can resolve these problems early in the conversion effort and can serve as a guideline for a full scale conversion process. A mechanism for maintaining communication between the contractor and client for identification of any anomalies in the source materials, situations not taken into account by written specifications, or errors in data conversion throughout the conversion process should be developed. Once a problem is identified, the contractor and the client should work together to resolve the problem. The accepted resolution should then be used to modifi the workplan for the data conversion. QC should not be thought of as merely “catching contractor mistakes”. While the primary purpose of carrying out QC procedures is to identifi and correct errors in delivered products, the QC process serves many fimctions:
- Quality control insures that the digital database is complete in its content of graphic features and associated attributes.
- Quality control familiarized users at the Commission with their digital database and its uses. Carrying out quality control procedures provides an opportunity to identi~ anomalies in source documents and to correct them.
- Digital quality control familiarizes users at the Commission with their GIS software and its capabilities.
- Quality control develops a level of confidence in the digital database among users at the Commission.
