[gdal-dev] What should I expect?

[Jorge Arevalo]

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 <chapmanm at pixia.com> 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-bounces at lists.osgeo.org
> [mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of Jorge Arevalo
> Sent: Friday, August 10, 2012 9:39 AM
> To: gdal-dev at 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 at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev



-- 
Jorge Arevalo
http://www.libregis.org