GeoInfo

Projection information is stored in a pre-defined structure named GeoInfo.

define structure GeoInfo
  char Units[24] ! Map Units string (16 characters maximum)
  double ULX     ! Upper left X coordinate in georef units
  double ULY     ! Upper left Y coordinate in georef units
  double LRX     ! Lower right X coordinate in georef units
  double LRY     ! Lower right Y coordinate in georef units
  double XOff    ! X offset in georef units of upper left corner
  double YOff    ! Y offset in georef units of upper left corner
  double XSize   ! X size in georef units that each pixel represents
  double YSize   ! Y size in georef units that each pixel represents
  double XRot    ! X rotation for the georeference area
  double YRot    ! Y rotation for the georeference area
  double DEarth1 ! Semi-major axis for the earth in meters
  double DEarth2 ! Semi-minor axis for the earth in meters
  double RefLong       ! Reference Longitude
  double RefLat        ! Reference Latitude
  double StdParallel1  ! First standard parallel
  double StdParallel2  ! Second standard parallel
  double FalseEasting  ! False Easting in meters
  double FalseNorthing ! False Northing in meters
  double Scale         ! Scale for some projections
  double Height        ! If Units are “GVNP”, meters above the earth
  double Long1         ! If Units are “OM”, Longitude of first point on center line
  double Lat1          ! If Units are “OM”, Latitude of first point on center line
  double Long2         ! If Units are “OM”, Longitude of second point on center line
  double Lat2          ! If Units are “OM”, Latitude of second point on center line
  double Azimuth       ! If Units are “OM”, azimuth east of north for center line
  integer LandsatNum   ! If Units are “SOM”, the Landsat number
  integer LandsatPath  ! If Units are “SOM”, the Landsat path
enddefine

The most important field is the Units field, which contains the map unit string that defines the georeferencing system. For Example, from irvine.pix this would be "UTM 11 S E000". The ULX, ULY, LRX and LRY fields are the positions of the upper left and lower right corners of the raster to which this projection information corresponds. The ULX, ULY, LRX, and LRY fields have been down-graded and are now derived from the XOff, YOff, XSize, YSize, XRot, and YRot fields and the raster layer dimensions in DBReadGeoInfo(). In DBWriteGeoInfo(), the ULX, ULY, LRX, and LRY have no effect and it is XOff, YOff, XSize, YSize, XRot, and YRot that are written to the output file. When the GeoInfo is related to a vector layer, a meaningful value will not be set.

The remaining fields are special values used only for some of the complex projections. Complex projections are those for which the map unit string does not fully define the projection. UTM, SPCS and LONG are Examples of simple projections defined fully by the Units value, while Transverse Mercator and Lambert Conformal Conic are Examples of projections that require additional values.

See also

DBReadGeoInfo()

VECReadGeoInfo()

Reproject()