[gdal-dev] What should I expect?
Hello, 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 -- Jorge Arevalo http://www.libregis.org ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
Re: [gdal-dev] What should I expect?
Jorge, It's a south up image. If the gsd x value is negative the image is an east to west image. Normally a north up image will have a positive gsd x and a negative gsd y. Marty -Original Message- From: gdal-dev-boun...@lists.osgeo.org [mailto:gdal-dev-boun...@lists.osgeo.org] On Behalf Of Jorge Arevalo Sent: Friday, August 10, 2012 9:39 AM To: gdal-dev@lists.osgeo.org Subject: [gdal-dev] What should I expect? Hello, 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 -- Jorge Arevalo http://www.libregis.org ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
Re: [gdal-dev] What should I expect?
Hi, Many thanks for your response, Martin. So, it doesn't need to be a mistake. Just a flipped image. The doubt raised because, for example, gdalbuildvrt doesn't accept ns positive resolution values. Looking at this old ticket http://trac.osgeo.org/gdal/ticket/3432, seems that that kind of raster data can't be mosaiced. You get an error. I don't understand why. I know cartesian coordinate system sets the origin in the bottom left corner, while images set the origin in the top left corner. So, the ns resolution of a georeferenced image is negative. Otherwise, you get a south up image. But... if all the images you want to mosaic have this "problem" (positive ns resolution), why I can't mosaic them using gdalbuiltvrt? Best regards, Jorge On Fri, Aug 10, 2012 at 6:09 PM, Martin Chapman wrote: > Jorge, > > It's a south up image. If the gsd x value is negative the image is an > east to west image. Normally a north up image will have a positive gsd x > and a negative gsd y. > > Marty > > -Original Message- > From: gdal-dev-boun...@lists.osgeo.org > [mailto:gdal-dev-boun...@lists.osgeo.org] On Behalf Of Jorge Arevalo > Sent: Friday, August 10, 2012 9:39 AM > To: gdal-dev@lists.osgeo.org > Subject: [gdal-dev] What should I expect? > > Hello, > > 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 > > -- > Jorge Arevalo > http://www.libregis.org > ___ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev -- Jorge Arevalo http://www.libregis.org ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
Re: [gdal-dev] What should I expect?
Le vendredi 10 août 2012 22:28:34, Jorge Arevalo a écrit : > Hi, > > Many thanks for your response, Martin. So, it doesn't need to be a > mistake. Just a flipped image. > > The doubt raised because, for example, gdalbuildvrt doesn't accept ns > positive resolution values. Looking at this old ticket > http://trac.osgeo.org/gdal/ticket/3432, seems that that kind of raster > data can't be mosaiced. You get an error. I don't understand why. > > I know cartesian coordinate system sets the origin in the bottom left > corner, while images set the origin in the top left corner. So, the > ns resolution of a georeferenced image is negative. Otherwise, you get > a south up image. But... if all the images you want to mosaic have > this "problem" (positive ns resolution), why I can't mosaic them using > gdalbuiltvrt? Jorge, You could certainly remove this limitation of gdalbuildvrt. I put it because I'm lazy and don't usually deal with south-up images (and because images with postive ns resolution are in 99% of the cases in fact ungeoreferenced images, which you don't want to mosaic). I suspect that just removing the test might make things work. I let you experiment with that. ___ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
