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

Wed Jun 10 23:18:52 EST 2015

Ari,

It looks like you have a raster with classified pixel values. If the number
of RGB sets is not more than 256, you can convert it to 8 bit paletted
image using rgb2pct.py. Then you will have a single band to represent all
colors and a single value to represent the set (230,245,255) which can be
set as nodata.

Also, if you look at the example in the doc page of that script, there is a
way to create a color table. You can edit that vrt file to set the pixels
with those values to transparent by setting c4 to 0.

http://www.gdal.org/rgb2pct.html

On Wed, Jun 10, 2015 at 11:42 PM Ari Simmons <ari.ucb.fire at gmail.com> wrote:

> Hm. Yeah. I don't think this is going to work...
>
> I need to remove whatever pixel has the 3 values ' 230, 245, 255'
> ...which is different then removing from Band 1 = 230, Band 2 = 245, Band 3
> = 255. If I do that, I am 'NoData'ing' values I probably want to keep (for
> ex: '230 246 255' would become '0 246 0'....not right.)
>
> Ok. So to do this another way...is there an elegant way to go from a 3
> Band to a 1 Band image (other then just taking 1 of the 2 bands). I know
> there is a way to go from a Grayscale 1-band to a 3-band RGB ...but is
> there an inverse of that?
>
>
>
>
>
> On Wed, Jun 10, 2015 at 10:53 AM, <Matt.Wilkie at gov.yk.ca> wrote:
>
>>  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> 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] *On Behalf Of *Ari Simmons
>> *Sent:* Wednesday, June 10, 2015 10:19 AM
>> *To:* Chaitanya kumar CH
>> *Cc:* 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> 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>
>> 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> 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 * 867-393-7003 Fax
>> http://environmentyukon.gov.yk.ca/geomatics/
>> --------------------------------------------
>>
>>
>>
>> -----------------------------
>>
>> From: 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
>> 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.
>>
>>
>>
>> _______________________________________________
>> FWTools mailing list
>> FWTools at lists.maptools.org
>> http://lists.maptools.org/mailman/listinfo/fwtools
>> http://fwtools.maptools.org/
>>
>>   --
>>
>> Chaitanya Kumar CH
>>
>>
>>
>>
>>
>
> --

Chaitanya Kumar CH
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