# [postgis-users] SRTM Raster Geometry question

Ed Linde edolinde at gmail.com
Sun Mar 4 11:39:31 PST 2012

```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?

On Sun, Mar 4, 2012 at 8:30 PM, yvecai <yvecai at gmail.com> wrote:

> **
> It seems to me that the SRTM dataset is available in tiles of 1°x1°, with
> a 3 arc second resolution, which gives a raster of 1200x 1200 pixels. 3 arc
> second is ~90 meter, but *exactly* 3 arc second in WGS84.
> http://dds.cr.usgs.gov/srtm/version2_1/Documentation/Quickstart.pdf
> Yves
>
> Le 04/03/2012 19:36, Ed Linde a écrit :
>
> Yves, I am not sure I understand what you are saying..sorry. My question
> is basically if the points within a single cell can
> potentially have different elevation values because of interpolation? Or
> do all the points that lie within a cell get one elevation
> value?
>
> On Sun, Mar 4, 2012 at 2:36 PM, yvecai <yvecai at gmail.com> wrote:
>
>>  Le 04/03/2012 14:14, Ed Linde a écrit :
>>
>>  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.
>>
>>  Cheers,
>> Ed
>>
>>
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>>
>>  Wouldn't that be a grid of 1°/1201 by 1°/1201 with 1201x1201 elevation
>> value?
>> Just a guess.
>> Yves
>>
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