[FWTools] gdal_merge with a specific pixel value clipped/removed

Wed Jun 10 12:53:23 EST 2015

That vrt snippet looks correct. Only one nodata number per band, and it has the correct value, 230.

In my test file 2 or so lines above <ComplexSource> there is an additional line “<NoDataValue>” with the number as a scaled float, “1.80000000000000E+001” (the +001 at end means move decimal to right 1 time. My nodata here is “18”). Full file is attached.

Matt

From: Ari Simmons [mailto:ari.ucb.fire at gmail.com]
Sent: Wednesday, June 10, 2015 10:24 AM
To: Matt.Wilkie
Cc: Chaitanya kumar CH; fwtools at lists.maptools.org
Subject: Re: [FWTools] gdal_merge with a specific pixel value clipped/removed

Matt

Not sure I see how...

    <ComplexSource>
      <SourceFilename relativeToVRT="1">TEX_N00E006.tif</SourceFilename>
      <SourceBand>1</SourceBand>
      <SourceProperties RasterXSize="1200" RasterYSize="1200" DataType="Byte" BlockXSize="1200" BlockYSize="2" />
      <SrcRect xOff="0" yOff="0" xSize="1200" ySize="1200" />
      <DstRect xOff="0" yOff="0" xSize="1200" ySize="1200" />
      <NODATA>230</NODATA>
Do you mean change

 <NODATA>230</NODATA>
to

 <NODATA>230 245 255</NODATA>

On Wed, Jun 10, 2015 at 10:20 AM, <Matt.Wilkie at gov.yk.ca<mailto:Matt.Wilkie at gov.yk.ca>> wrote:
Perhaps try editing the .vrt file with a text editor and changing the nodata value by hand?

Matt

From: fwtools-bounces at lists.maptools.org<mailto:fwtools-bounces at lists.maptools.org> [mailto:fwtools-bounces at lists.maptools.org<mailto:fwtools-bounces at lists.maptools.org>] On Behalf Of Ari Simmons
Sent: Wednesday, June 10, 2015 10:19 AM
To: Chaitanya kumar CH
Cc: fwtools at lists.maptools.org<mailto:fwtools at lists.maptools.org>
Subject: Re: [FWTools] gdal_merge with a specific pixel value clipped/removed

Ok - so gdal_translate works great! Thanks!

HOWEVER, the removal of value 230 245 255 is still no happening...when I put in:

>>gdalbuildvrt -srcnodata "230 245 255" tif_index.vrt *.tif

I get a .vrt with Band 1 = 0 (instead of 230) and the full 3 Band value becoming (0 245 255)....not what I expected. I expected it to become "NoData"....

On Tue, Jun 9, 2015 at 9:17 PM, Chaitanya kumar CH <chaitanya.ch at gmail.com<mailto:chaitanya.ch at gmail.com>> wrote:
Ari,

The vrt is an xml file that represents a single raster dataset made up of one or many rasters. So, it is already merged. You can read it using any good text editor.
You only have to run gdal_translate to convert it to a tif.

gdal_translate -of GTiff tif_index.vrt tif_index.tif

On Wed, Jun 10, 2015 at 2:40 AM Ari Simmons <ari.ucb.fire at gmail.com<mailto:ari.ucb.fire at gmail.com>> wrote:
Interesting...ok, so (knowing nothing about .vrt's and having a bunch of .tiff's) I ran this:
>>gdalbuildvrt -srcnodata "230 245 255" tif_index.vrt *.tif
0...10...20...30...40...50...60...70...80...90...100 - done.
then

>> gdal_merge -o merged_result.tif *.vrt
and got

ERROR 4: `*.vrt' does not exist in the file system,

and is not recognised as a supported dataset name.
I'm on OSGEO4W too..

On Tue, Jun 9, 2015 at 1:24 PM, <Matt.Wilkie at gov.yk.ca<mailto:Matt.Wilkie at gov.yk.ca>> wrote:
The error is because you need to quote the argument values to keep them from being interpreted as filenames:

        gdal_merge -n “230 245 255” ...

However gdal_merge can't use different nodata values for each band. You need to pre-process the files before merging. This worked for me here:

Create  VRT (virtual raster) file for the input file(s):

        gdalbuildvrt -srcnodata "230 245 255”"  infile1.vrt  infile1.tif

Then feed the .vrt's to gdal_merge:

        gdal_merge -of merged_result.tif infile1.vrt infile2.vrt ...

You may need to switch from fwtools to Osgeo4w (if on Windows) to get gdalbuildvrt.

Cheers,

--
matt wilkie
--------------------------------------------
Geomatics Analyst
Information Management and Technology
Yukon Department of Environment
10 Burns Road * Whitehorse, Yukon * Y1A 4Y9
867-667-8133<tel:867-667-8133> Tel * 867-393-7003<tel:867-393-7003> Fax
http://environmentyukon.gov.yk.ca/geomatics/
--------------------------------------------

-----------------------------

From: fwtools-bounces at lists.maptools.org<mailto:fwtools-bounces at lists.maptools.org> [mailto:fwtools-bounces at lists.maptools.org<mailto:fwtools-bounces at lists.maptools.org>] On Behalf Of Ari Simmons
Sent: Tuesday, June 09, 2015 12:43 PM
To: fwtools at lists.maptools.org<mailto:fwtools at lists.maptools.org>
Subject: [FWTools] gdal_merge with a specific pixel value clipped/removed

I have a large set of .tif files and I need to merge/mosaic them all into one .tif with the no-data value removed (i.e. value 230, 245, 255). However, when I put this in...pixel '230, 245, 255' becomes '0, 245, 255').
I am trying to get NO PIXEL returned for 230, 245, 255. Is that possible?
I:\TFS_6\trial_merge>gdal_merge.py -o test.tif -n 230 245 255 file1.tif file2.tif

ERROR 4: `245' does not exist in the file system,
and is not recognised as a supported dataset name.

ERROR 4: `255' does not exist in the file system,
and is not recognised as a supported dataset name.

0...10...20...30...40...50...60...70...80...90...100 - done.

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--

Chaitanya Kumar CH

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