[gdal-dev] Fwd: Re: Alpha band masking

Even Rouault even.rouault at spatialys.com
Tue Nov 17 10:23:52 PST 2015 

----------  Message transmis  ----------

Sujet : Re: [gdal-dev] Alpha band masking
Date : mardi 17 novembre 2015, 19:08:06
De : MUTLU OZDOGAN <ozdogan at wisc.edu>
À : Even Rouault <even.rouault at spatialys.com>

Dear Even,

It turns out that the problem was on my end!  I was clipping the input image 
to corner coordinates that was outside of the input image and hence the 0 
values.

Thank you so much for you help.

Mutlu..


On Nov 17, 2015, at 10:50 AM, Even Rouault 
<even.rouault at spatialys.com<mailto:even.rouault at spatialys.com>> wrote:

Le mardi 17 novembre 2015 10:19:59, Mutlu Ozdogan a écrit :
Yes I have removed the xml file sorry I forgot to include that

Try also adding "-co alpha=no -overwrite" to the gdalwarp command line,
although it shouldn't have any influence on the pixel values at that stage.


Sent from my iPhone

On Nov 17, 2015, at 3:04 AM, Even Rouault 
<even.rouault at spatialys.com<mailto:even.rouault at spatialys.com>>
wrote:

Le mardi 17 novembre 2015 04:08:41, MUTLU OZDOGAN a écrit :
Dear Even,

The result of the gdalinfo -mm command is this:

Driver: GTiff/GeoTIFF
Files: pr026029_5m.tif

     pr026029_5m.tfw

Size is 35921, 41035
Coordinate System is:
PROJCS["NAD83(HARN) / Wisconsin Transverse Mercator",

  GEOGCS["NAD83(HARN)",

      DATUM["NAD83_High_Accuracy_Reference_Network",

          SPHEROID["GRS 1980",6378137,298.2572221010002,

              AUTHORITY["EPSG","7019"]],

          AUTHORITY["EPSG","6152"]],

      PRIMEM["Greenwich",0],
      UNIT["degree",0.0174532925199433]],

  PROJECTION["Transverse_Mercator"],
  PARAMETER["latitude_of_origin",0],
  PARAMETER["central_meridian",-90],
  PARAMETER["scale_factor",0.9996],
  PARAMETER["false_easting",520000],
  PARAMETER["false_northing",-4480000],
  UNIT["metre",1,

      AUTHORITY["EPSG","9001"]]]

Origin = (296789.742753763101064,562520.115095380693674)
Pixel Size = (5.000000000000000,-5.000000000000000)

Metadata:
AREA_OR_POINT=Area

Image Structure Metadata:
INTERLEAVE=PIXEL

Corner Coordinates:
Upper Left  (  296789.743,  562520.115) ( 92d51'25.45"W, 45d30' 1.70"N)
Lower Left  (  296789.743,  357345.115) ( 92d46' 5.00"W, 43d39'20.14"N)
Upper Right (  476394.743,  562520.115) ( 90d33'30.53"W, 45d32' 5.47"N)
Lower Right (  476394.743,  357345.115) ( 90d32'27.79"W, 43d41'16.23"N)
Center      (  386592.243,  459932.615) ( 91d40'51.66"W, 44d36' 1.34"N)
Band 1 Block=35921x1 Type=Byte, ColorInterp=Red

  Computed Min/Max=0.000,255.000

Mask Flags: PER_DATASET ALPHA

Band 2 Block=35921x1 Type=Byte, ColorInterp=Green

  Computed Min/Max=0.000,255.000

Mask Flags: PER_DATASET ALPHA

Band 3 Block=35921x1 Type=Byte, ColorInterp=Blue

  Computed Min/Max=0.000,255.000

Mask Flags: PER_DATASET ALPHA

Band 4 Block=35921x1 Type=Byte, ColorInterp=Alpha

  Computed Min/Max=0.000,255.000

the exact commands I used are:

gdal_translate  pr026029_5m.tif tmp.tif -co alpha=no

--> Did you remove tmp.tif.aux.xml as I mentionned before ?

Note: given the use of gdalwarp you make, you could also just use
gdal_translate -projwin instead (caution: the order of arguments is not
the same since -projwin expect upper_left_x upper_left_y lower_right_x
lower_right_y)

then

gdalwarp -te 422861.999 225313.018 489606.999 308903.018 -tr 5 5 tmp.tif
out.tif

The results of the out.tif is the problematic output as all the bands
are zeros as in:

Driver: GTiff/GeoTIFF
Files: out.tif
Size is 13349, 16718
Coordinate System is:
PROJCS["NAD83(HARN) / Wisconsin Transverse Mercator",

  GEOGCS["NAD83(HARN)",

      DATUM["NAD83_High_Accuracy_Reference_Network",

          SPHEROID["GRS 1980",6378137,298.2572221010002,

              AUTHORITY["EPSG","7019"]],

          AUTHORITY["EPSG","6152"]],

      PRIMEM["Greenwich",0],
      UNIT["degree",0.0174532925199433]],

  PROJECTION["Transverse_Mercator"],
  PARAMETER["latitude_of_origin",0],
  PARAMETER["central_meridian",-90],
  PARAMETER["scale_factor",0.9996],
  PARAMETER["false_easting",520000],
  PARAMETER["false_northing",-4480000],
  UNIT["metre",1,

      AUTHORITY["EPSG","9001"]]]

Origin = (422861.999000000010710,308903.017999999981839)
Pixel Size = (5.000000000000000,-5.000000000000000)

Metadata:
AREA_OR_POINT=Area

Image Structure Metadata:
INTERLEAVE=PIXEL

Corner Coordinates:
Upper Left  (  422861.999,  308903.018) ( 91d11'47.57"W, 43d14'48.02"N)
Lower Left  (  422861.999,  225313.018) ( 91d10'55.54"W, 42d29'38.70"N)
Upper Right (  489606.999,  308903.018) ( 90d22'27.90"W, 43d15' 8.35"N)
Lower Right (  489606.999,  225313.018) ( 90d22'11.62"W, 42d29'58.50"N)
Center      (  456234.499,  267108.018) ( 90d46'50.60"W, 42d52'26.06"N)
Band 1 Block=13349x1 Type=Byte, ColorInterp=Red

  Computed Min/Max=0.000,0.000

Mask Flags: PER_DATASET ALPHA

Band 2 Block=13349x1 Type=Byte, ColorInterp=Green

  Computed Min/Max=0.000,0.000

Mask Flags: PER_DATASET ALPHA

Band 3 Block=13349x1 Type=Byte, ColorInterp=Blue

  Computed Min/Max=0.000,0.000

Mask Flags: PER_DATASET ALPHA

Band 4 Block=13349x1 Type=Byte, ColorInterp=Alpha

  Computed Min/Max=0.000,0.000

Thank you so much.

Mutlu..



On Nov 16, 2015, at 3:21 AM, Even Rouault
<even.rouault at spatialys.com<mailto:even.rouault at spatialys.com><mailto:even.rouault at spatialys.com>> 
wrote:

Le samedi 14 novembre 2015 22:26:48, Mutlu Ozdogan a écrit :
Dear Evan
Thank you so much for the input. I actually tried exactly those steps
and unfortunately I still get 0s in the output file. Thank you again

Could you post the result of "gdalinfo -mm your_input_file.tif" and the
exact GDAL commands you use ?

Mutlu

Sent from my iPhone

On Nov 14, 2015, at 1:00 PM, Even Rouault
<even.rouault at spatialys.com<mailto:even.rouault at spatialys.com><mailto:even.rouault at spatialys.com>> 
wrote:

Le samedi 14 novembre 2015 19:49:02,
ozdogan at wisc.edu<mailto:ozdogan at wisc.edu><mailto:ozdogan at wisc.edu> a écrit : 
Dear All
I have a 4-band air photo image in which the 4th band is the NIR band
but it has also been designated as an alpha band. It is the geotiff
format. For some reason whenever I reproject this file (using gdalwarp)
or resize it (using gdal_translate) all four bands of the resulting
files have zero values. It is as if the alpha band is being used to
mask all band values. Any help reprojecting or windowing this large
file without making while retaining all 4 band values would be much
appreciated. Thank you

Mutlu,

The issue is probably indeed the NIR band being recognized as an alpha
band. You can remove the alpha interpretation with :

gdal_translate in.tif tmp.tif -co alpha=no
rm tmp.tif.aux.xml (or del tmp.tif.aux.xml on Windows)

The removal of tmp.tif.aux.xml is important otherwise the alpha
interpretation would be kept in this XML file

And then you can gdalwarp this tmp.file with the arguments you need :

gdalwarp tmp.tif ...

Even

--
Spatialys - Geospatial professional services
http://www.spatialys.com


--
Mutlu Ozdogan, Ph.D.
Associate Professor
Department of Forest and Wildlife Ecology &
Nelson Institute for Environmental Studies
t: (608) 262-0873
e: ozdogan at wisc.edu<mailto:ozdogan at wisc.edu>

--
Spatialys - Geospatial professional services
http://www.spatialys.com


--
Mutlu Ozdogan, Ph.D.
Associate Professor
Department of Forest and Wildlife Ecology &
Nelson Institute for Environmental Studies
t: (608) 262-0873
e: ozdogan at wisc.edu<mailto:ozdogan at wisc.edu>





-------------------------------------------------------
-- 
Spatialys - Geospatial professional services
http://www.spatialys.com

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