[SOLVED]Read and display geotiff images.

ealione

Is it possible to display a GeoTiff image in Qt?
I would prefer not having to use OpenCV though, so if any of you had any idea on how this is done I would appreciate any examples or some other recourse to get me started.

SGaist

Hi,

Are you interested in reading only the image or also the metadata ?

ealione

Hi SGaist,

I would actually be interested in having the metadata too, because I want to calculate the total distance of the image (in meters).
But if that is not possible to do then just the image should be fine.

SGaist

Unless I'm mistaken (please correct me if I'm wrong) but GeoTiff uses tiff, which is already supported by Qt however I don't think you can access the meta data directly maybe using QImageReader::textKeys() and friends.

ealione

I will try that and report back. The textKeys, suggestion I mean.

ealione

@SGaist I tried using textKeys but unfortunately they report nothing back when I try to search about available text keys.

What I do get though are warnings of the type

TIFFReadDirectory: Warning, Unknown field with tag 33550 (0x830e) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 33922 (0x8482) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 34735 (0x87af) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 34736 (0x87b0) encountered.
...

That are actually tags but there seems to be no method of reading them.

SGaist

That's what I feared. You could open a feature request on the bug report system and use a library like GDAL in-between to get the tags.

ealione

Indeed I should.
Seems like geotiflib is a good solution. Actually reading the tags should be actually pretty easy. I mean that it can be achieved with minimal changes to the existing tiff parser, so hopefully this wont be an issue on future releases.

ealione

Issue opened here.

SGaist

If you need to do it for your project anyway, you could improve the tiff parser from Qt :)

ealione

Yeah as I said above, I had a quick look and I believe it can be done relatively with ease. I will definitely give it a try as soon as I find some time :)