Mytable where gid in (" & theList & ") order by st_length(the_geom) I digged in the dirty dust and found this: SELECT gid,
Then I just created the image-map by writing the returned string with asp, or if it was php. The query sent to PostGIS, makes a simplified buffer around the geometry in the right pixelscale and recalculates since the image map has it's origin in upper left corner and the projection of the map has it's origin of course in the lower left corner. Two years ago I used it to build an click-able html image map on a gif-image delivered from mapserver. "ST_Affine - Applies a 3d affine transformation to the geometry to do things like translate, rotate, scale in one step." Because almost all GIS processing-spatial indexes, spatial relations, spatial queries, "geoprocessing," etc-uses algorithms based on the Euclidean geometry of the map, affine transformations are fundamental to GIS. For example, every regular grid of locations is affinely equivalent to the grid of points with integral coordinates and all ellipsoidal models of the earth are affinely equivalent to the unit sphere centered at the origin.įinally, note that ( at least since the late 1800's) Euclidean geometry is the study of the group of distance-preserving affine transformations. Other hits provide many more examples.Īffine transformations also provide some conceptual simplifications. These are described in more detail and illustrated for the 2D case on this Web page, which is found when you search "affine transformation GIS".
Modifying features by rescaling, shifting, and rotationĭatum changes (3-point and 7-point formulas).
Routine uses of 2D and 3D affine transformations in GIS include
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