Changes between Initial Version and Version 1 of rfc58_removing_dataset_nodata_value

Timestamp:

May 12, 2015, 9:23:38 AM (9 years ago)

Author:

sgillies

Comment:

Formatting

rfc58_removing_dataset_nodata_value

@@ +1 @@
+= RFC 58: Removing Dataset Nodata Value =
+
+Authors: Sean Gillies
+
+Contact: sean at mapbox.com
+
+Status: Draft
+
+== Summary ==
+
+This RFC adds a GDALDeleteNoDataValue() function to the GDAL C API. This function removes a dataset's nodata value. When it succeeds, the dataset will have no nodata value. When it fails, the nodata value will be unchanged.
+
+== Rationale ==
+
+In the C API the nodata value has accessors {{{GDALGetNoDataValue()}}} and {{{GDALSetNoDataValue()}}}. For GeoTIFFs, the value is stored in a TIFFTAG_GDAL_NODATA TIFF tag. Newly created GeoTIFF files can have no nodata value (no tag), but once a nodata value is set and stored it can only be given new values, it can not be removed. Nor can it be set to a value outside the range of the data type; for 8-bit data passing {{{nan}}}, {{{-inf}}}, or {{{256}}} to {{{GDALSetNoDataValue()}}} has the same effect as passing 0.
+
+The problem with un-removable nodata values is this:
+
+ * Nodata masks (see GDAL RFC 15) can cover up a nodata value but if the .msk file gets lost (and this is ever the problem with sidecar files), the nodata value you were hiding is exposed again.
+ * Nodata masks are not available everywhere in GDAL, nodata values are the only definition of valid data in some parts of GDAL.
+
+The current recommended practice for removing a nodata value is to copy the GeoTIFF using gdal_translate, specifying that the nodata tag not be copied over along with the data. By making the nodata value fully editable and removable we could avoid copying unnecessarily.
+
+== Changes ==
+
+{{{GDALDeleteNoDataValue()}}} will be added to gdal.h.
+
+=== Updated drivers ===
+
+The following drivers will be updated: GTiff, MEM, VRT.
+
+The {{{GDALPamRasterBand}}} class will also be updated (for drivers that have no built-in mechanism nodata mechanism and rely on .aux.xml sidecars).
+
+== SWIG bindings (Python / Java / C# / Perl) changes ==
+
+No changes to the SWIG bindings are proposed. 
+
+== Utilities ==
+
+No changes to utilities are proposed.
+
+== Documentation ==
+
+No new documentation is proposed.
+
+== Test Suite ==
+
+TBD.
+
+== Compatibility Issues ==
+
+None.
+
+== Implementation ==
+
+Implementation will be done by Even Rouault and be sponsored by Mapbox.
+
+== Voting history