[Gdal-dev] AIGReadBlock failure to read some ArcInfo Grid tiles

[Olsen, Keith]

Hello,

 

I am new to GDAL so forgive me if this issue has already been addressed.

 

I am using the GDAL AIG driver to read arcInfo grids with values that
range from 0-5.6 million.  When I read one of these grids I get the
following warning from gridlib.c:

 

Warning 1: Unsupported Arc/Info Binary Grid tile of type 0x20
encountered.

This and subsequent unsupported tile types set to no data value.

 

The read does not crash my program, but it skips 10-20% of the 4x256
pixel tiles in my image.  The non-skipped tiles seem to be read
correctly.  When I clip out a smaller area with a dropped tile, I get
the same problem.  The grids can be read in arcInfo and arcMap with no
problems.

 

Some common characteristics of these 'bad' blocks as they are read in
the function 'AIGReadBlock' are as follows:

 

nBlockSize = 4100 or 4104

nMagic = 32

nMarker = 0 (in AIGProcessBlock)

 

nMin seem to be read correctly in both good and bad blocks.

 

Another clue is that the range of values in the few 'bad' blocks I
examined is quite large (>1 million).

 

Any ideas or suggestions would be appreciated.  I can also send anyone
copies of the grid tiles that are not being read correctly.

 

Thanks,

 

--Keith

 

===============================================

Keith Olsen                     /\

Oregon State University        /  \/\     |

Keith.Olsen at oregonstate.edu <mailto:Keith.Olsen at oregonstate.edu>     /
\  \ ---o---

(541) 750-7279                / || \ \

===============================================

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/gdal-dev/attachments/20040528/fbf64349/attachment.html