[postgis-devel] [PostGIS] #985: [raster] ST_Count
PostGIS
trac at osgeo.org
Fri May 27 14:06:04 PDT 2011
#985: [raster] ST_Count
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Reporter: dustymugs | Owner: dustymugs
Type: task | Status: reopened
Priority: medium | Milestone: PostGIS 2.0.0
Component: postgis raster | Version: trunk
Resolution: | Keywords: history
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Comment(by dustymugs):
Yes, all the functions you mentioned could be changed.
case 1) SELECT ST_ValueCount(ST_SetBandNodataValue(rast, NULL))
The above is NOT as fast as
case 2) SELECT ST_ValueCount(rast, FALSE, ...)
This isn't as significant for small rasters (100 x 100) versus large
rasters (10000 x 10000) due to the time required for:
1. For ST_SetBandNodataValue, deserialize raster
2. set hasnodata flag
3. serialize raster
4. For ST_ValueCount, deserialize raster
5. process pixels
6. return counts
For case 2, on steps 4, 5 and 6 would occur vs steps 1 through 6 for the
two step. So, maybe we should keep the "hasnodata" and just give it a
better name?
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Ticket URL: <http://trac.osgeo.org/postgis/ticket/985#comment:14>
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