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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

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1 Answer 1

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.

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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

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