[postgis-users] Detecting wrong geometries

[Andrea Peri]

>Hi,
>
>Polygon orientation is not important with respect to OGC
>specifications and does not define an invalid polygon.
>That's why st_isvalid() returns true in Postgis.
>You can, however, force polygon orientation using the st_forceRHR()
>function (http://postgis.refractions.net/docs/ST_ForceRHR.html).
>
>Nicolas


Thx for clear response.

But I like to understand better why this strategy.

When load from a shapefile with shp2pgsql the source of data is a shapefile
with follow the ESRI specifics, and it is not an OGC source.
So the meaning of the geometry in the shapefile must following the specific
of the esri document.

This mean that a geometry counter-clockwise is a hole, or is a mistake.
If it is a hole then if the goal is to load exactly what there is in the
shapefile is needed to load the hole :).
If it is a mistake then is needed report the mistake and not load that
geometry.
I prefer the first choice of course, but I'm not sure to understand why load
something else that is changed from the original is better.

-- 
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Andrea Peri
. . . . . . . . .
qwerty àèìòù
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