[postgis-users] SRTM Raster Geometry question

Puneet Kishor punk.kish at gmail.com
Sun Mar 4 14:43:36 PST 2012

Yves is absolutely correct. Each pixel that is "no data" is a separate value.

On Mar 4, 2012, at 3:25 PM, yvecai wrote:

> I think one pixel= one elevation value, and :
> "File names refer to the latitude and longitude of the lower left corner of
> the tile - e.g. N37W105 has its lower left corner at 37 degrees north
> latitude and 105 degrees west longitude. To be more exact, these
> coordinates refer to the geometric center of the lower left pixel, which in
> the case of SRTM3 data will be about 90 meters in extent."
> All the doc is here:
> http://dds.cr.usgs.gov/srtm/version2_1/Documentation/
> ;-)
> Yves
> Le 04/03/2012 20:53, Mr. Puneet Kishor a écrit :
>> On Mar 4, 2012, at 1:39 PM, Ed Linde wrote:
>>> Thanks Yves, but my question still remains though. So in this raster of
>>> 1200 x 1200 pixels, does each pixel get assigned an elevation in meters of
>>> "x" meters? Or do the four corners of each pixel have different elevation
>>> values of a,b,c and d meters each?
>>> ..
>> I am guessing (albeit, based on my fiddling with SRTM a long time ago) that it is an ave value of "x" meters assigned to all the pixels in the tile. In essence, a 1200 pixel-square tile is behaving like a single large pixel with a value of "x" meters.
>> Should be easy to confirm it by querying a few random pixels in a tile.
>> --
>> Puneet Kishor

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