MS RFC 4: MapServer Raster Resampling

Date:

2005/09/16

Author:

Frank Warmerdam

Contact:

warmerdam at pobox.com

Status:

adopted

Version:

MapServer 4.8

Overview

Additional resampling kernels will be implemented in the MapServer GDAL raster resampler code including « averaging », « bilinear » and « cubic ».

Technical Details

• The new resampling options will be implemented in mapresample.c and will only be accessible for datasets processing through that mechanism (ie. GDAL raster formats, requires coordinate system information defined).

• The resampling kernel to use will be selected with one of the following. The default will be RESAMPLE=NEAREST, the current behavior.

  PROCESSING "RESAMPLE=NEAREST"
  PROCESSING "RESAMPLE=AVERAGE"
  PROCESSING "RESAMPLE=BILINEAR"
  

• The mapraster.c code currently decides whether to invoke the « simple » GDAL renderer or the « resampling » GDAL renderer based on whether the projection seems to differ. It will also now check for the RESAMPLE processing option, and force use of mapresample.c if the resampling kernel select is other than NEAREST.

• Note that resampling kernels other than NEAREST can have a substantial effect on rendering performance. For this reason NEAREST will remain the default.

Mapfile Implications

All new options are selected via new PROCESSING options. There is no change in the mapfile syntax. There should be no compatibility problems with old mapfiles.

MapScript Implications

There are no additions or changes to the MapScript API. The new options are controlled via PROCESSING information on the layers which I believe is already manipulatable from MapScript.

Documentation Implications

The new processing options will need to be documented in the Raster Data (and possibly the MAP reference).

Test Plan

New test cases for each mode will be incorporated in msautotest/gdal.

Staffing / Timeline

The new feature will be implemented by Frank Warmerdam and completed by October 15th, 2005, in time for the MapServer 4.8 release. Implementation is generously funded by Tydac AG and managed by DM Solutions.