What is the meaning of the Pixel Size field in the gdalinfo
output on a TIFF image?
I have 2 images, one is a PAN image (size 400MB) while one is a DEM (size 25MB). Both are in TIFF format. When I run the gdalinfo
command on these 2, I get the following:
For the PAN image:
Pixel Size = (0.600000023841858,-0.600000023841858)
For the DEM:
Pixel Size = (0.000277777777778,-0.000277777777778)
I also get the same values (with one extra value) when I run another command, exiftool
, on these 2 images:
For the PAN image:
Pixel Scale : 0.600000023841858 0.600000023841858 0
For the DEM:
Pixel Scale : 0.000277777777778 0.000277777777778 0
I can see that the output is same, except that gdalinfo
puts a minus
sign before second value, and exiftool
gives 3 values where the 3rd value is 0
.
What should I infer from these values? Which image has a better spatial resolution? I know its the PAN image that has a better resolution, but how do I understand that from these values?
I say this because since 0.00027 < 0.6, so one might think that the DEM has a better resolution. Just like when we say that an image has a spatial resolution of 0.25 meter while other has 0.3 meter resolution, it means the 0.25 meter one (the lower one) has better resolution. Or maybe I am understanding it wrong if I'm looking at the value of the number in this case.
Whats the unit of these numbers? Is it meters? If not, then what? Which gdalinfo
field could tell me the unit? Right now I get this metadata field in gdalinfo
which has the word 'unit' in it:
TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
How to I explain someone that in this context, bigger number means better resolution, not the other way?
Some additional info that I feel might be helpful:
The metadata field AREA_OR_POINT is as follows:
For the PAN: - POINT
For the DEM: - AREA