The part that isn't trivial is that square pixels in 4326 are highly non square on the ground if your area of interest is not near the equator.
Common translations between projections (such as using gdal_warp -r cubic -t_srs EPSG:4326) will create an output file with fewer pixels in the north-south direction than a source file (tested with source file in UTM). Thus, data is lost and will not be recovered when transforming back to UTM or Web Merc later. This isn't to say the problem is intractable but it isn't entirely obvious either. (You can use the -tr option to set different x and y resolutions for the output but then the resolutions need to be calculated manually.) Also, some form of this issue occurs somewhere with any global projection and isn't specific to 4326. My take on why 4326 is because any global projection has problems an 4326 is most universally understood and supported. Why not support many? Because of the problems of understanding every possible coordinate system. It is easier to push the conversion to the data providers (who understand their local projection and 4326) than all the data consumers. Also many non-trivial reprojections internally go through 4326 anyway. On Nov 7, 2011, at 8:49, Josh Doe <[email protected]> wrote: > Brian, > Is it any more trivial than the reverse? Sorry, but I don't see how > that is an argument for EPSG:4326, it is an argument that can just as > easily be applied to any (global) projection. > -Josh > > On Mon, Nov 7, 2011 at 9:36 AM, Brian Case <[email protected]> wrote: >> josh >> >> its trivial to re-project 4326 to web merc on the fly >> >> Brian >> >> On Mon, 2011-11-07 at 07:40 -0500, Josh Doe wrote: >>> I've been trying to find the discussion or rationale for why EPSG:4326 >>> is the projection of choice (or only supported projection?), but >>> haven't had any luck. It seems to me that most imagery will eventually >>> be consumed in EPSG:3857/900913, though of course not exclusively, so >>> it seems that would be a better choice. Is there any technical reasons >>> why EPSG:4326 is preferred, or any statistics on it being more >>> prevalent? I think the answer to this belongs in the docs. >>> >>> Thanks, >>> -Josh >>> >>> _______________________________________________ >>> talk mailing list >>> [email protected] >>> http://host134.hostmonster.com/mailman/listinfo/talk_openaerialmap.org >> >> >> > > _______________________________________________ > talk mailing list > [email protected] > http://host134.hostmonster.com/mailman/listinfo/talk_openaerialmap.org _______________________________________________ talk mailing list [email protected] http://host134.hostmonster.com/mailman/listinfo/talk_openaerialmap.org
