Christopher Hunt wrote:
Hi there,
Being new to gdal I'm hoping that someone can help me by verifying my
gdal_translate command. Thanks in advance.
I have an aerial photo of an airport which I therefore assume is
orthographic. Three points have been provided to me which I am assuming
to be wgs84:
point1 = -0.49310374, 51.47858961
point2 = -0.46551585, 51.47177116
point3 = -0.43439870, 51.46490423
The x and y pixel positions appear to be as follows:
61, 115
465, 280
899, 435
I then determine the easting/northing values using proj:
> proj +proj=ortho +datum=WGS84
> -0.49310374 51.47858961
-34186.74 4990098.00
> -0.46551585 51.47177116
-32278.95 4989625.23
> -0.43439870 51.46490423
-30125.85 4989149.04
> ^C
Given the above is this the correct command to geocode my image?
> gdal_translate -a_srs '+proj=ortho +datum=WGS84' \
-gcp 61 115 -34186.74 4990098.00 \
-gcp 465 280 -32278.95 4989625.23 \
-gcp 899 435 -30125.85 4989149.04 \
inputfile.jpg outputfile.tif
I ask because if I subsequently warp using:
gdalwarp -t_srs '+proj=eqc +datum=WGS84' -dstalpha -multi outputfile.tif
outputfile-eqc.tif
...then things don't look quite right... (a 1024x650 image becomes a
2923x456 image).
Chris,
Given your assumptions I believe you have done things properly. I would
suggest you question your assumptions - particularly that the image is
in an orthographic projection and that if it is in an orthographic
projection that default lat_0 and lon_0 values are appropriate.
Best regards,
--
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I set the clouds in motion - turn up | Frank Warmerdam, [EMAIL PROTECTED]
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