I'm not sure of the PostGIS functions you'd use to do this, but
geometrically you could:
For projection onto the Y axis:
- extract the linework of the input geometry
- scale it by (0, 1)
- flatten the resulting mess of linestrings by unioning them
Mutatis mutandis for the X axis.
Kostis Kyzirakos wrote:
Hi All!
This may be a naive question, but I am not sure how to do a cartesian
projection in PostGIS (version 1.5).
Assume that we have a table MySpatialGeometries(id integer, geo geometry),
and a tuple with id 10 and geo the rectangle POLYGON(0 0 0,1 0 0,1 0 1,0 0
1,0 0 0).
How may I calculate the cartesian projection of the geometry along the x,y
or z axis?
For example, how can I make the following calucations:
1. project on x-axis (project out y,z), result: Linestring (0 0 0, 1 1 0)
2. project on y-axis (project out x,z), result: Point (0 0 0)
3. project on x,y axis (project out z), result: Linestring (0 0 0, 1 1 0)
4. project on x,z axis (project out y), result: Polygon(0 0 0,1 0 0,1 0 1,0
0 1,0 0 0).
etc.
I think that I can express case 3 using the Force2D function.
But how can I express the other cases?
Thanks for your help!
Cheers,
Kostis
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Refractions Research, Inc.
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