How to process geometrical data from a spatial database

Asked Jun 23 '14 at 07:51

Active Jun 23 '14 at 07:51

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I'm working on a small geographical project, and I'm having a small trouble with one thing. I have a spatial database (SpatiaLite) in which I store some geometries (it has geometry columns). Specifically - polygons. They are stored of course as BLOB objects in the database. Now I would like to query the database, retrieve this geometry object and the process it so that I can for example plot it later. The way I see it, there are two ways of doing that: either extract the raw BLOB, and then decode it somehow, or fetch its well-known text representation using the SpatiaLite AsText (Geometry) command. The result would look like:

POLYGON ((0, 5), (3, 4) ...)

Not really sure which way is better, any advice how to approach this? The implementation is done in Python 2.7.

asked Jun 23 '14 at 07:51

Michał Szydłowski

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Map drawing libraries typically know about WKB. How do you want to plot them? – CL. Jun 23 '14 at 07:52
Until now I just used matplotlib. – Michał Szydłowski Jun 23 '14 at 07:53
Try one, and if you can't get it to work come back for help. – monkut Jun 23 '14 at 07:55
But it's not a matter of trying and error, the thing is, that I'm stuck and I just don't know how to proceed with either one. – Michał Szydłowski Jun 23 '14 at 07:57
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your suggestion, "fetch its well-known text representation using the SpatiaLite AsText (Geometry) command", seems like a good place to start. – monkut Jun 23 '14 at 08:02
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shapely can load wkb or wkt if your having trouble parsing. http://toblerity.org/shapely/manual.html – monkut Jun 23 '14 at 08:04
Yes, exactly what I needed, I dunno how could I miss it. Thanks a lot! – Michał Szydłowski Jun 23 '14 at 08:06
Here's Spatialite's BLOB structure : http://gaia-gis.it/gaia-sins/BLOB-Geometry.html – tema Sep 15 '14 at 09:08

How to process geometrical data from a spatial database

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