2

I'm trying to convert this TIF to EPSG:3857, but when I run:

gdalwarp -of GTiff -s_srs epsg:4326 -t_srs epsg:3857 -co "tfw=yes" original.tif converted.tif

I just get a black TIF do you know what I am doing wrong?

Command output

> gdalwarp -of GTiff -s_srs epsg:4326 -t_srs epsg:3857 -co "tfw=yes" original.tif converted.tif
Creating output file that is 4088P x 4105L.
Processing input file original.tif.
Using band 2 of source image as alpha.
0...10...20...30...40...50...60...70...80...90...100 - done.
  • Are you sure the input is WGS84 Geographic? Have you adjusted the contrast of the output? Sometimes a very high value pixel or nodata value can make all valid values appear black or near black and a good contrast stretch will fix that. I can see that it is... perhaps the alpha band is tricking it. – Michael Stimson Nov 19 '14 at 1:36
  • Where did you view the tiff? – R.K. Nov 19 '14 at 1:47
  • @R.K. the TIF is in the link in the question. – nickponline Nov 19 '14 at 1:48
  • @MichaelMiles-Stimson I have't done anything else to the image except run the gdalwarp comment. It says it's using band 2 as alpha. Can I do a contrast stretch with gdal? – nickponline Nov 19 '14 at 1:50
  • No contrast stretch is in the software you're using to view the image (like QGIS). It worked for me on just the first band, how important is the alpha channel? – Michael Stimson Nov 19 '14 at 1:52
2

I think it's the alpha band that's causing problems. To extract the data band:

gdal_translate -of hfa -b 1 original.tif band1.img

Then to warp:

gdalwarp -of GTiff -s_srs epsg:4326 -t_srs epsg:3857 -co "tfw=yes" band1.img band1_warp.tif

Gives an image:

enter image description here

With GDALINFO

> Driver: GTiff/GeoTIFF Files: D:\Testing\Tiff\band1_warp.tif
>        D:\Testing\Tiff\band1_warp.tif.ovr
>        D:\Testing\Tiff\band1_warp.tfw
>        D:\Testing\Tiff\band1_warp.tif.aux.xml Size is 4088, 4105 Coordinate System is: PROJCS["WGS 84 / Pseudo-Mercator",
>     GEOGCS["WGS 84",
>         DATUM["WGS_1984",
>             SPHEROID["WGS 84",6378137,298.257223563,
>                 AUTHORITY["EPSG","7030"]],
>             AUTHORITY["EPSG","6326"]],
>         PRIMEM["Greenwich",0],
>         UNIT["degree",0.0174532925199433],
>         AUTHORITY["EPSG","4326"]],
>     PROJECTION["Mercator_1SP"],
>     PARAMETER["central_meridian",0],
>     PARAMETER["scale_factor",1],
>     PARAMETER["false_easting",0],
>     PARAMETER["false_northing",0],
>     UNIT["metre",1,
>         AUTHORITY["EPSG","9001"]],
>     EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs"],
>     AUTHORITY["EPSG","3857"]] Origin = (-13520950.132675199000000,4662178.034760829100000) Pixel Size =
> (0.081230547006398,-0.081230547006398) Metadata:   AREA_OR_POINT=Area 
> DataType=Generic Image Structure Metadata:   INTERLEAVE=BAND Corner
> Coordinates: Upper Left  (-13520950.133, 4662178.035) (121d27'38.74"W,
> 38d35' 0.40"N) Lower Left  (-13520950.133, 4661844.583)
> (121d27'38.74"W, 38d34'51.97"N) Upper Right (-13520618.062,
> 4662178.035) (121d27'28.00"W, 38d35' 0.40"N) Lower Right (-13520618.062, 4661844.583) (121d27'28.00"W, 38d34'51.97"N) Center   
> (-13520784.097, 4662011.309) (121d27'33.37"W, 38d34'56.19"N) Band 1
> Block=4088x2 Type=Byte, ColorInterp=Gray   Description = Layer_1  
> Overviews: 2044x2053, 1022x1027, 511x514, 256x257, 128x129   Metadata:
>     DESCRIPTION=Layer_1
>     LAYER_TYPE=athematic

Wierdly when warping with an alpha band the entire band becomes 0 (transparent) but when extracting and warping the 2nd band:

gdal_translate -of hfa -b 2 original.tif band2.img
gdalwarp -of GTiff -s_srs epsg:4326 -t_srs epsg:3857 -co "tfw=yes" band2.img band2_warp.tif

it looks fine... then stack the bands back together:

gdal_merge.py -separate -o stacked.tif band1_warp.tif band2_warp.tif

and the image is warped with a correct alpha band.

Further testing indicates that it could be the input tiff that is causing the alpha band to become bad:

gdal_translate -of hfa original.tif original_as.img
gdalwarp -of GTiff -s_srs epsg:4326 -t_srs epsg:3857 -co "tfw=yes" original_as.img warp_from_img.tif

Produces the correct image alpha band: Band 1 Band 1

Band 2 (alpha) Band 2

As warping from the img no longer sees the second band as an alpha band.

| improve this answer | |
  • That's interesting, any idea why the alpha channel is causing issues. Ideally I'd like to retain it in the final image - is that possible? – nickponline Nov 19 '14 at 2:01

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