On Mar 4, 2012, at 4:43 PM, Puneet Kishor wrote: > Yves is absolutely correct. Each pixel that is "no data" is a separate value.
whereby, I meant that each pixel that is NOT a "no data" is one elevation value. `gdallocationinfo` can happily query each pixel (or lng/lat) quite efficiently. > > > 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 >>> > _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
