Why do mappers need control and intelligence anyway ?
Structuring Intelligent Maps
The key to understanding a resources management information systems is the general concept of levels or layers. Information in the system can be vowed as being sorted by type and stored in a series of separate layers. For different purposes selected layers can be retrieved from the system and combined in a multiplicity of combinations. The RMS can contain tens or hundreds of layers of data concerning the soils, slope stability, geology, forest cover types, wildlife habitat, flood hazards. Seismic hazards, property or lease information. Predominant land use and other data types deemed pertinent to the user. Each classification f data usually contains two types of information which may reside on one or two layers: descriptive text and the locational descriptors.
The most important layer of any functional RMS is the geodetic control information. The function of this layer is to provide a common reference base for precise alignment of multiple themes of resource information. Land and resources can be described in many ways: but each systems requires a physical point or series of points as reference. Proper management requires an accurate description
of location: a reference frame work tied to monumented geodetic control points is essential to permit subsequent combination of information from multiple layers.
Another important layers is the cadastral information of ownership parcel boundaries and data relating to the ownership or lease of the property. In most Asia-Pacific countries property ownership is the primary land entity which defines the location and the rights to the use of the land. Clearly, there is a need for accurate and continuous updating of ownership boundaries with in a specific jurisdiction to which all other layers of information may be referenced through the use of a unique indexing system. This index is critical to management of the land inv3ntory within the RMS and the parole is the fundamental unit of the digital information.
The third important layer is the cartographic representation of the land base. Once the geodetic control has been established, the major land features that can be easily identified are placed on the appropriate base map layers. Transportation, streams, lakes, political boundaries, and cultural information are commonly included in the cartographic layers. These “base map” features make it easier to visually locate other information in the system.
Control Issues
Control information is one f the most important and critical issues to be considered in developing any digital resource management system (RMS). Appreciation of the value of control information may be established if one recognizes the essentially of its utilization in:
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Scaling and orientation of imagery and graphic spatial data
- Establishment of ground coordinate systems
- Transformation from one coordinate system to others
- Map merging processes
- Quality assurance of spatial data
There are several techniques that may be utilized to obtain control data which frequently are categorized into two major methods, Geodetic and Photo grammetric.
Geodetic Mmethod
Various types of geodetic observation are introduced in order to precisely determine the spatial positions of some natural or artificial ground monuments. These observations may consist of a collection of distances, angles and coordinate differences.
Global positioning systems (GPS) may be considered as the most modern techniques of geodetic control data acquisition which generally consists of tracking, receiving and recording, specific satellite signals. These signals are digitally processed in combination with signal codes (Ephemeris) in order to compute three dimensional coordinates ground positions.
The more conventional geodetic techniques consist of angular and distance measurements. These measurements are processed taking into consideration the curvature of the surface of the earth. The result of the process is geodetic coordinates systems. The conversion process depends upon the adopted map projection as well al ellipsoid parameters.
For smaller areas of the earth, the conventional ground surveying geodetic techniques can be utilized to provide minor control as a well as data collection of ground feature details. In these local area case, the effect of earth curvature may be neglected since its influence is too small to be considered (the difference between the chord and are distance of 18.5 km is 1.0 cm).
Geodetic techniques are the most accurate methods of providing control for referencing of special data. However, collection of data on feature details using this method maybe considered costly as time consuming.
