[postgis-users] Postgis Raster determine exact hull

[Richard Huesken]

hi,

I'm using postgis 3.1 and I'm looking for the best way to obtain the exact hull of a raster (excluding the nodata points). The st_minconvexhull uses the MBR of the raster coverage, and is therefore quite fast. The result is however not as accurate as I require.

I constructed some sql that uses st_pixelaspolygons and then does a st_union. However, My typical raster has 256x256 points, and with several 100s of rasters this is quite slow.

Are there more clever (and faster!) ways to get the exact hull of a raster?

Thanks in advance,

Richard.

[Marcin Mionskowski]

Hi,

Try to reclassify the raster first so that all "non NA" values are equal (e.g. 1), then do ST_DumpAsPolygons.

Regards,

Marcin

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[Regina Obe]

You could also try using ST_Polygon

 

It will treat all non NA as the same resulting in a polygon or multipolygon.

 

https://postgis.net/docs/RT_ST_Polygon.html