Fix bug in getdxdyc for parallel runs

[jcphill]

linearpart::getdxdyc() would silently fail to return values
for neighbor cells from other ranks, resulting in bad AreaDinf output.

[dtarb]

Do you have an example where this actually causes a problem. I have not investigated this specifically now, but I am skeptical because Areadinf has been tested a lot with multiple processes and ranks, and I think the approach used of having the buffer row at the bounds of each rank, and swapping after each pass likely prevents an actual error.

[jcphill]

Yes, in TauDEM-Test-Data/Input/Geographic running "mpiexec -np XXX AreaDinf enogeo.tif" with different rank counts gives enogeosca.tif files for which gdalcompare.py reports pixel differences (thousands of pixels but maximum difference of 2 or so).

[dtarb]

Thanks. I'll check it out.

[jcphill]

Example output (from original, unfixed version):

$ mpiexec -n 1 ../../../build/areadinf -ang enogeoang.tif -sca enogeosca1.tif
AreaDinf version 5.3.9
Input file enogeoang.tif has geographic coordinate system.
This run may take on the order of 1 minutes to complete.
This estimate is very approximate.
Run time is highly uncertain as it depends on the complexity of the input data
and speed and memory of the computer. This estimate is based on our testing on
a dual quad core Dell Xeon E5405 2.0GHz PC with 16GB RAM.
Nodata value input to create partition from file: -340282346638528859811704183484516925440.000000
Nodata value recast to float used in partition raster: -340282346638528859811704183484516925440.000000
Processors: 1
Read time: 0.137529
Compute time: 1.248470
Write time: 0.041544
Total time: 1.427543
$ mpiexec -n 12 ../../../build/areadinf -ang enogeoang.tif -sca enogeosca12.tif
AreaDinf version 5.3.9
Input file enogeoang.tif has geographic coordinate system.
Nodata value input to create partition from file: -340282346638528859811704183484516925440.000000
Nodata value recast to float used in partition raster: -340282346638528859811704183484516925440.000000
This run may take on the order of 1 minutes to complete.
This estimate is very approximate.
Run time is highly uncertain as it depends on the complexity of the input data
and speed and memory of the computer. This estimate is based on our testing on
a dual quad core Dell Xeon E5405 2.0GHz PC with 16GB RAM.
Processors: 12
Read time: 0.028167
Compute time: 0.140669
Write time: 0.033118
Total time: 0.201954
$ gdalcompare.py enogeosca1.tif enogeosca12.tif
Files differ at the binary level.
Band 1 checksum difference:
Golden: 5380
New: 5431
Pixels Differing: 31527
Maximum Pixel Difference: 1.875
Differences Found: 2

[jcphill]

Do you have time to look at this?

[dtarb]

Sorry - I have not had time yet.