[gdal-dev] Mosaicking Orthos

[Chaitanya kumar CH]

Zoltan,

The creation of 0394w.tif failed. Does the process have write permission on
directory?
I note that you did not specify the -of option for nearblack. In it's
absence, nearblack creates the output file in Erdas Imagine format.


On Sun, Feb 20, 2011 at 10:50 PM, Zoltan Szecsei <zoltans at geograph.co.za>wrote:

>  Hi Chaitanya (& all),
> I tried your nearblack comment, and got:
>
>  nearblack -white -o 0394w.tif 0394.tif
> Warning 1: TIFFFetchNormalTag:ASCII value for tag "ImageDescription" does
> not end in null byte
>


> Warning 1: TIFFFetchNormalTag:ASCII value for tag "ImageDescription" does
> not end in null byte
> Warning 1: TIFFFetchNormalTag:ASCII value for tag "Software" contains null
> byte in value; value incorrectly truncated during reading due to
> implementation limitati
> ERROR 4: Creation of file 0394w.tif failed.
>
>
> I think I am having trouble understanding the setting/using of nodata
> values.
> I have now also downloaded and compiled gdal 1.8.0 (but nearblack remained
> on v1.7.3) on ubuntu 10.04 LTS, and recreated my vrt, to no improvement.
>
> To recap: I have 179 3*8bit RGB band aerial images that have been
> orthorectified. The resulting skewness in the images has created white
> slivers in the corners, and I am presuming that these white slivers are
> recognised as "nodata". (My first mistake?)
>
> I use the following to create a vrt:
> gdalbuildvrt -addalpha -hidenodata -srcnodata "255 255 255" -vrtnodata "0 0
> 0" -input_file_list files 177_untiled_orthos_nodata_180.vrt
>
> Thinking that the above will tell gdalbuildvrt that, for the input orthos,
> white should be recognised as 'nodata', and in the VRT, those white pixels
> should be converted to black, as nodata.
> Well, as you've guessed, it didn't happen this way, and I still have the
> white bits after mosaicking my VRT thus:
> gdal_translate -projwin -16000 -3520650 -13000 -3525650
> 177_untiled_orthos_nodata.vrt try1.tif
>
> I tried re-running gdalbuildvrt specifying -vrtnodata "255 255 255" (to
> match the input ortho files) and the outside border of my vrt turned white,
> but the slivers between the mosaicked orthos were still present.
>
> Please can someone show me the correct way to address this problem.
>
> I have included gdalinfo results for both an individual ortho, and for the
> vrt itself.
>
> Thanks & regards,
> Zoltan
>
>
>
>
>
>
> **********************************  *GDALINFO on indicidual ORTHO*****************************************
> geograph at gs0:~/vrt_177$ *gdalinfo --version*
> GDAL 1.8.0, released 2011/01/12
> geograph at gs0:~/vrt_177$
> geograph at gs0:~/vrt_177$
> geograph at gs0:~/vrt_177$
> geograph at gs0:~/vrt_177$ *gdalinfo
> /mnt/geo_lvm0/ngi_jobs/orthos_8bit/NGI_177_untiled_orthos/0003.tif*
> Warning 1: TIFFFetchNormalTag:ASCII value for tag "ImageDescription" does
> not end in null byte
> Warning 1: TIFFFetchNormalTag:ASCII value for tag "Software" contains null
> byte in value; value incorrectly truncated during reading due to
> implementation limitations
>


>   Mask Flags: PER_DATASET ALPHA
> Band 4 Block=128x128 Type=Byte, ColorInterp=Alpha
> geograph at gs0:~/vrt_177$
>
> *******************************************************************************************************
>
>
>
>
> On 2011-02-16 19:39, Chaitanya kumar CH wrote:
>
> Zoltan,
>
> Have you tried the nearblack GDAL utility on the original 176 images?
> http://www.gdal.org/nearblack.html
>
> On Wed, Feb 16, 2011 at 5:25 PM, Zoltan Szecsei <zoltans at geograph.co.za>wrote:
>
>> On 2011-02-16 12:20, Zoltan Szecsei wrote:
>>
>>> Hi All,
>>> I've built a vrt with 176 images.
>>>
>>> I now need to mosaic this whole area into roughly 5 x 5 ortho images.
>>>
>>> How can I force the white edges into background of the overlapping
>>> orthos?
>>> I'm a little cautious of simply (finding a way to) making "white"
>>> transparent as it is only the white on the edges that need to be
>>> backgrounded.
>>>
>>
>>  Hi again,
>> Since the above post, I have tried different ways to set nodata, but to no
>> avail - I still get the white edges:
>> (see jpeg sent with my original post)
>>
>> gdalbuildvrt -addalpha -hidenodata -input_file_list files
>> 177_untiled_orthos_nodata.vrt
>> gdalbuildvrt -srcnodata "0 0 0"  -addalpha -hidenodata -input_file_list
>> files 177_untiled_orthos_blk.vrt
>> gdalbuildvrt -srcnodata "255 255 255"  -addalpha -hidenodata
>> -input_file_list files 177_untiled_orthos_white.vrt
>>
>> How should I be masking out the nodata (or even white pixels) so that when
>> I mosaic a bunch of tiffs together, I dont get the white stripes in the
>> resulting image?
>>
>> Using GDAL 1.7.3, released 2010/11/10 on Ubuntu 10.04
>> Viewing with Quantum GIS - 1.6.0-Trunk on Ubuntu 10.04 (same box).
>> ...but running the whole lot in xterms with Xming & putty from my WinVista
>> box.
>>
>>
>> Regards,
>>
>> Zoltan
>>
>>
>
> --
>
> ===========================================
> Zoltan Szecsei PrGISc [PGP0031]
> Geograph (Pty) Ltd.
> P.O. Box 7, Muizenberg 7950, South Africa.
>
> 65 Main Road, Muizenberg 7945
> Western Cape, South Africa.
>
> 34° 6'16.35"S 18°28'5.62"E
>
> Tel: +27-21-7884897  Mobile: +27-83-6004028
> Fax: +27-86-6115323     www.geograph.co.za
> ===========================================
>
>  ------------------------------
>
>
>
>

-- 
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
17.2416N 80.1426E
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