[postgis-users] SRTM Raster Geometry question

Bistrais, Bob Bob.Bistrais at maine.gov
Mon Mar 5 07:05:56 PST 2012

You should check the metadata for the layer.  But by convention, cell
values on a raster layer are generally the value at the center of each



From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Ed
Sent: Sunday, March 04, 2012 8:14 AM
To: PostGIS Users Discussion
Subject: [postgis-users] SRTM Raster Geometry question


Hi All,

Can someone help me understand a concept with the SRTM raster. My
understanding is that the raster can be thought of as a uniform grid
with each cell having dimension =  "90m x 90m" (for SRTM-1 dataset). Now
I am just wondering if the elevation values are 4 values at each vertex
or boundary point of a cell? or is it one elevation value for the 90x90
m^2 area covered by the cell? I ask because if its the first option,
then it would mean that every point that falls in the cell has it's
elevation calculated using some sort of interpolation between the 4
corner points of the cell to arrive at this point's altitude. Or do
several points that fall into this 90x90 cell get assigned the same
elevation value?

Would be great if I could get some help understanding this concept about
SRTM rasters.




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