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2012.11.21 06:33 "XTIFFClientOpen scheme not generating proper geotiff tags", by Oscar Kramer
2012.11.21 19:12 "Re: XTIFFClientOpen scheme not generating proper geotiff tags", by Ryan Wong

2012.11.21 06:33 "XTIFFClientOpen scheme not generating proper geotiff tags", by Oscar Kramer


I am trying to use XTIFFClientOpen in order to read and write geotiff 
files from within the hadoop HDFS file system. I followed the examples 
provided for implementing the read, write, seek, close, and other 
functions required. I am able to successfully open and read a geotiff 
from HDFS using this scheme. However, writing a geotiff image is not 
working properly.

The output file is missing what seem to be geotiff-specific tags, though 
I'm not sure (I'm comparing hex dumps of a good file against a bad). The 
differences are just two bytes near the very beginning of the file, 
namely, the offset to the first IFD. The good file has 0x0C0008 while 
the bad one just has 0. The only other difference is at the end of the 
file where the good one has about 680 bytes (starting at offset 
0x0C0008) while the bad just ends at 0x0C0008. All the data in between 
-- which appears to be pixel data -- is identical.

I bypassed all the HDFS stuff and had my client functions 
read/write/seek using just the local FS to eliminate that variable and I 
see the same thing, so the problem is not HDFS related.

I am using the same code for populating and writing the tags as I do 
when interfacing to the geotiff lib using the conventional XTIFFOpen 
function.  In both instances I'm calling GTIFWriteKeys() after 
populating the keys. What baffles me is that I don't see my write 
function being called within GTIFWriteKeys.

I suspect that the issue is with the close function not properly 
flushing the geo-tags. The only thing my client close function does is 
actually close the file -- just a one-liner with no additional writes of 
any kind.

Is there something special (i.e., geotiff-specific) I need to do when 
using XTIFFClientOpen and its i/o functions to insure the geotiff tags 
get written out?