Tell me more ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.
up vote 2 down vote favorite

If while I'm executing gdalinfo against a raster layer I get a positive value for pixel size Y, what of these scenarios is possible?

  • The raster's map coordinate system sets the origin of the data in the upper left corner.
  • The raster is not georeferenced and its coordinates are interpreted as image pixels, instead of map units.
  • Any other situation (corrupt file?, other?)

I know this value is almost always negative. For example, in case of UTM coordinate system. But, how common is to have a positive value for Y coordinate?

Many thanks in advance

share|improve this question

1 Answer

up vote 2 down vote accepted

from wikipedia

http://en.wikipedia.org/wiki/World_file#cite_note-2

"..This is because most image files store data from top to bottom, while the software utilizes traditional Cartesian coordinates with the origin in the conventional lower-left corner. If your raster appears upside-down, you may need to add a minus sign. The parameter therefore describes the map distance between consecutive image lines."

So you are right, if the origin is at top-left the distance between consecutive image line is positive and hence positive Y values.

share|improve this answer
Mmmm... still a doubt. I know cartesian coordinate system sets the origin in the bottom left corner, while images do it in the top left corner. So, in georeferenced images, you need a negative Y resolution, otherwise you get a south up image. Ok so far. But, for example, why doesn't gdalbuildvrt accept positive y resolutions? If this doesn't mean a mistake, just a flipped image, what's the problem? – jorgeas80 Aug 10 '12 at 20:32

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.