WCS GetCoverage intermittent "skewed or rotated dataset" error

[keithmoss]

We're requesting a single pixel bounding box in XYZ output format and finding that MapServer will intermittently throw this error:

"msSaveImageGDAL(): General error message. Failed to create output XYZ file. XYZ driver does not support CreateCopy() from skewed or rotated dataset."

A 3x3 grid of pixels including the offending pixel works without issue.

The problem *seems* to repeat every 6 or so pixels horizontally and effects the entire column of pixels. The pixels either side of these columns work without issue.

See attached ZIP file for sample data and mapfile.

## Example ##

URL: SERVICE=WCS&VERSION=1.0.0&REQUEST=GetCoverage&COVERAGE=xyz_test_case&CRS=EPSG%3A4326&BBOX=115.5225%2C-32%2C115.525%2C-31.9975&FORMAT=XYZ&RESX=0.0025&RESY=0.0025

Returns: The aforementioned error.

The equivalent call to GDAL's Translate utility: gdal_translate -of XYZ -projwin 115.5225 -31.9975 115.525 -32 xyz_test_case.dat.ers extract4.txt

Returns: 115.52374999999999 -31.998750000000001 3783

Which is consistent with the value returned by the functioning 3x3 pixel grid.

## Additional Examples ##

Not Working: 115.5075 -31.9975 115.51 -32 (GDAL) - 115.5075, -32, 115.51, -31.9975 (MS)

Works: 115.5175 -32.01 115.52 -32.0125 (GDAL) - 115.5175, -32.0125, 115.52, -32.01 (MS)

MapServer version 6.0.0, GDAL 1.8, PHP MapScript ($Revision: 11619 $ $Date: 2011-04-27 12:23:07 -0300 (Wed, 27 Apr 2011) $)

We've opened another bug which may be related: ​http://trac.osgeo.org/mapserver/ticket/3993

[keithmoss]

Test case

[keithmoss]

We can also provide URLs to our development service for testing/verification if required.