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Geopositioning information (dataset coordinates vs
Geopositioning is used to establish a
mathematical relationship between the dataset coordinates space and the
Coordinate Reference System defined through the Georeferencing set of
information. Geopositioning can be performed in several different ways :
Geoposition_Insert, Geoposition_Points, Geoposition_Affine.
- The first type (Geoposition_Insert) is the most
commonly used for (ortho-)rectified datasets. In this case, the dataset
coordinate space is superimposable with the CRS. Suffice it to deliver a single
insertion point and a scale for both coordinate axis. For raster datasets; the
top left corner is then used as the insertion point and the ground size of a
pixel is given.
- The second type (Geoposition_Points) is generally
used for approximate geopositioning; it provides a set of points cited in both
coordinate spaces (dataset and CRS);it is up to the display system to build-up
a mathematical relationship in order ti interpolate between those points
(polynomial, rubbersheeting, ...).
- The third case (Geoposition_Affine) is used for
general linear transformation (rotation, scale, sheering). For instance, it can
be used to establish a simple coordinate matching between paper cordinates of a
scanned map and CRS coordinates.
Geopositioning types are exclusive to each
Datatype : t_Geoposition
One of :