On Fri, 2011-07-08 at 08:14 -0700, Michael Corey wrote:
OK, I did a little more work on this, and I've narrowed down what's
going on, but I could still use some help in figuring out how to solve it.
Here's my original image:
http://mikejcorey.com/spatial/diablo-orig-5pct.tif
The original appears to have an RGBA setup (RGB channels and an alpha
channel).
When I run this:
gdalwarp -crop_to_cutline -cutline cutout.shp sourceimage.tif
diablo-cutline.tif
Here's what I get:
http://mikejcorey.com/spatial/diablo-cutline-5pct.tif
This comes out as an RGB image with no alpha channel, with each channel
being semi-transparent.
Not in my case. Could there be something wrong with your GDAL
setup? I drew a shapefile mask and ran the above command but my
result is RGBA, the alpha band is not lost. See mask and result here:
http://ubuntuone.com/p/13WR/
the output of gdalinfo:
marius@mobi <mailto:marius@mobi>:~/Downloads$ gdalinfo
diablo_cutl.tif
Driver: GTiff/GeoTIFF
Files: diablo_cutl.tif
Size is 266, 224
Coordinate System is:
PROJCS["NAD83 / UTM zone 10N",
GEOGCS["NAD83",
DATUM["North_American_Datum_1983",
SPHEROID["GRS 1980",6378137,298.2572221010002,
AUTHORITY["EPSG","7019"]],
AUTHORITY["EPSG","6269"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433],
AUTHORITY["EPSG","4269"]],
PROJECTION["Transverse_Mercator"],
PARAMETER["latitude_of_origin",0],
PARAMETER["central_meridian",-123],
PARAMETER["scale_factor",0.9996],
PARAMETER["false_easting",500000],
PARAMETER["false_northing",0],
UNIT["metre",1,
AUTHORITY["EPSG","9001"]],
AUTHORITY["EPSG","26910"]]
Origin = (693798.721929854014888,3902305.751849883235991)
Pixel Size = (20.022668877344305,-20.040546259961307)
Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left ( 693798.722, 3902305.752) (120d52'12.04"W,
35d14'42.43"N)
Lower Left ( 693798.722, 3897816.669) (120d52'15.84"W,
35d12'16.81"N)
Upper Right ( 699124.752, 3902305.752) (120d48'41.44"W,
35d14'38.67"N)
Lower Right ( 699124.752, 3897816.669) (120d48'45.35"W,
35d12'13.05"N)
Center ( 696461.737, 3900061.211) (120d50'28.67"W,
35d13'27.75"N)
Band 1 Block=266x7 Type=Byte, ColorInterp=Red
Mask Flags: PER_DATASET ALPHA
Band 2 Block=266x7 Type=Byte, ColorInterp=Green
Mask Flags: PER_DATASET ALPHA
Band 3 Block=266x7 Type=Byte, ColorInterp=Blue
Mask Flags: PER_DATASET ALPHA
Band 4 Block=266x7 Type=Byte, ColorInterp=Alpha
-marius
However, if I do this:
gdalwarp -dstalpha -crop_to_cutline -cutline cutout.shp sourceimage.tif
diablo-dstalpha-cutline.tif
I get this:
http://mikejcorey.com/spatial/diablo-dstalpha-cutline-5pct.tif
This one is strange, because it appears to be a grayscale image. But
when I open it in Photoshop, I see that it actually has 4 alpha
channels. I suspect that those are just getting set incorrectly as alpha
and are in fact the RGB channels, but can someone explain that behavior
or how to fix it?
What I want to end up with is a clipped RGB image (or RGBA) image where
nodata is transparent and the RGB isn't translucent.
Thanks again!
Michael Corey
On 7/7/11 7:13 AM, Eli Adam wrote:
> Michael,
>
>>>> On 7/6/2011 at 5:35 PM, in message<[email protected]
<mailto:[email protected]>>, Michael
> Corey<[email protected] <mailto:[email protected]>> wrote:
>> Sure, I've uploaded samples here.
>>
>> http://www.mikejcorey.com/spatial/diablo-box-sample.tif
>> http://www.mikejcorey.com/spatial/diablo-cutout-sample.tif
> I don't notice the semi-transparency in these scaled down images. Perhaps
it is the way your viewer reads the mask?
>
>> These are the same as the images created by the process I described (but
>> scaled down).
>>
>> To your point about specifying size in the first step -- will that make
>> the process run faster, or does it do the scaling down after it builds
>> the full-resolution image?
>>
>> Also, I notice that my filesize always gets significantly bigger when I
>> do the cutout step, which seems counter-intuitive to me since in theory
>> shouldn't there be less information present once the cutout is done?
> -cutline does not 'discard' any data. The extent of the data remains the
same unless you reset those extents. You can do that with -crop_to_cutline. Here
are some details from the gdalwarp page,http://gdal.org/gdalwarp.html :
>
> -crop_to_cutline:
> (GDAL>= 1.8.0) Crop the extent of the target dataset to the extent of
the cutline.
>
> Polygon cutlines may be used as a mask to restrict the area of the
destination file that may be updated, including blending. If the OGR layer
containing the cutline features has no explicit SRS, the cutline features must be
in the georeferenced units of the destination file. When outputing to a not yet
existing target dataset, its extent will be the one of the original raster unless
-te or -crop_to_cutline are specified.
>
> Best Regards, Eli
>
>> Thanks for your help!
>>
>> Michael Corey
>>
>>
>> On 7/6/11 5:01 PM, Chaitanya kumar CH wrote:
>>> Michael,
>>>
>>> Can you provide screenshots of
>>> diablo-combined-center-utm10-70pct-box.tif and
>>> diablo-combined-center-utm10-70pct-cutout.tif for comparison?
>>>
>>> By the way, you can perform the actions of the two gdal_translate
>>> commands in the first step with the gdal_merge.py script itself unless
>>> you want to use a specific resampling algorithm.
>>>
>>> On Thu, Jul 7, 2011 at 4:28 AM, Michael Corey<[email protected]
<mailto:[email protected]>
>>> <mailto:[email protected]>> wrote:
>>>
>>> Hi all:
>>>
>>> I'm using a shapefile as a clipping mask to cut out the shoreline
>>> from some DOQ files that I have merged together. But when I do the
>>> clipping step, I end up with unwanted semitransparency in the
>>> non-clipped areas.
>>>
>>> I'm pretty sure the problem is only with my gdalwarp step at the end.
>>>
>>> Here's my process:
>>>
>>> gdal_merge.py -init "255" -o diablo-combined-center-utm10.tif file
>>> file file file
>>>
>>> gdal_translate -outsize 70% 70% diablo-combined-center-utm10.tif
>>> diablo-combined-center-utm10-70pct.tif
>>>
>>> ogrinfo -al ./diablo_canyon_detail_clipper.shp
>>> //Extent: (XXXX, YYYY) - (XXXX, YYYY)
>>>
>>> gdal_translate -projwin XXXX YYYY XXXX YYYY
>>> diablo-combined-center-utm10-70pct.tif
>>> diablo-combined-center-utm10-70pct-box.tif
>>>
>>> gdalwarp -co COMPRESS=DEFLATE -cutline
>>> ./diablo_canyon_detail_clipper.shp
>>> diablo-combined-center-utm10-70pct-box.tif
>>> diablo-combined-center-utm10-70pct-cutout.tif
>>>
>>> Can anyone help?
>>>
>>> Thanks!
>>>
>>> --
>>> Michael Corey
>>>
>>> _______________________________________________
>>> gdal-dev mailing list
>>> [email protected]
<mailto:[email protected]><mailto:[email protected]>
>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>
>>>
>>>
>>>
>>> --
>>> Best regards,
>>> Chaitanya kumar CH.
>>> /t?a???nj?/ /k?m?r/
>>> +91-9494447584
>>> 17.2416N 80.1426E
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