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AcDbGeoData Class

Class Hierarchy

AcRxObject
    AcGiDrawable
        AcDbObject
            AcDbGeoData

C++

class AcDbGeoData : public AcDbObject;

File

dbGeoData.h

Description

This object identifies the geographical space a design is located in. It also provides all the information necessary to accurately map a design coordinate system to a location on earth (a latitude-longitude based system). Furthermore this object provides a simple transformation to support efforts like Google Earth and geo-tagging and enough information to initialize geo-spatial applications for accurate coordinate system transformation and place a design on the earth, relative to each other.

The minimum requirements for a valid object are:

  1. Type of design coordinates.
  2. Design point.
  3. Reference point.
  4. A "design coordinate to geodetic coordinate" mesh with at least one point.
It is the association of the Design point and the Reference point which provides the minimum level of "georeferencing." Any application, regardless of its access to a coordinate conversion library, may obtain a georefernce for the object by calling one of the transformation functions with, for example, the values specified by the setDesignPoint function.

For many applications, this minimum level of georeferencing is adequate. Positioning a house within Google Earth, for example. To the degree that additional information is provided, more precise and comprehensive transformation results become available.

Note that if the design coordinate type is coordTypGrid, most all properties related to local coordinates are unused. Nevertheless, appropriate default values are specified.

Use of scale factors for units specifications are required as the number of linear units used in mapping applications exceeds by a substantial amount the number of units supported by the AcDb::UnitsValue enumeration. Also, occasionally it is necessary to support units which have not been encountered previously.

Finally, under normal circumstances, this object is created by the original application. That is the application which actually posts this object to the database. Consuming applications should consider this object to be a constant. The design, however, does not require that.

Links

AcDbGeoData Enumerations, AcDbGeoData Methods

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