[postgis-devel] OGC TIN of triangles or polygons?

Olivier Courtin olivier.courtin at oslandia.com
Mon Dec 2 01:53:44 PST 2013

On Dec 2, 2013, at 12:44 AM, Brent Wood wrote:


> The same applies to a rectangle - 5 points stored instead of 4 - so where do we draw the line? 
> How many vertices must a polygon have before we follow the spec & explicitly close it?

Well the point was not to want to change anything in the spec implementation (e.g WKT/WKB import/export)
but 'only'  a thought on the PostGIS triangle internal representation, 
in order to avoid redundant coordinates internal storage.

On Polygon it will be harder to do the same, because a Polygon could have several rings
(a triangle not), so if we wanted to do so (e.g flag is_closed on polygon), 
we would loose information on which rings is/are not closed (if any).

> I agree that the closing vertex is redundant, & can be replaced by a bit in the header - but by doing so we lose the ability to test for is it REALLY closed, rather than just saying it is closed, perhaps less important for triangles, but a capability I'm reluctant to lose.

As the flag would be internal, the only information lost, for triangles, would be: 
what are the final coordinates if unclosed (and so invalid).

But i agree it's already a lost.

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