[postgis-devel] wktraster ST_ConvexHull

[Jorge Arevalo]

Hello Regina,

On Tue, Apr 6, 2010 at 3:14 AM, Paragon Corporation <lr at pcorp.us> wrote:
> I'm a little bit confused about what ST_ConvexHull is supposed to return. I
> thought it would return the convex hull
> of the polygon formed by the pixels that aren't the BandNoDataValue value.
>
> It seems to always return the same result as ST_Envelope regardless of what
> I set the ST_BandNoDataValue too.

The resulting polygon from implemented ST_ConvexHull function encloses
every pixel, even those containing NODATA values. You can read the
specs here http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking01#Objective0.1.6e-Beingabletointersectvectorandrastertoproducevector.

Anyway, that point is not included in final specs yet. So, comments
are welcome. Pierre can provide more qualified opinion.

Best regards,
Jorge