using color tables for petascope output

[joachim.ungar@…]

The Snow Maps have a specific color scheme (please see the attached example.tif). Is there any possibility to add colors from a color table to a TIFF or PNG ​WPCS request WCPS output?

Applying customized colors facilitates the output interpretation, e.g. in vertical slices shown in this ​mock up.

Options:

• Associate a colormap to a coverage upon its creation (requiress specific metadata/schema change?)
• Send a colormap along with the request (could become cumbersome?)
• Apply a colormap on the client upon visualization (fast/feasible)?

[abeccati]

Alternative solutions are available for that function and will be suggested

[abeccati]

Looks like there were not many alternative solutions, this is also relevant for other domains using categorical data such as the Corine Land Cover dataset. The GeoTIFF version of it comes with a color table which is lost when loading it as a coverage or map.

PS the linked mock-up is not available anymore, maybe attaching it to the ticket would be better if not too large.

A possible solution, requiring no schema changes, would be to use the metadata field of the coverage.

An interim solution for such maps could be to define a "metadata extension" defining:

• an attibute "type" with value "colortable"
• an attribute "format" with value "tiff|png|…" depending on the source image (in case a conversion is needed to use it with other formats)
• the content being the raw colortable from the input (or the same metadata field from another coverage, or a well known interoperable format for it)

This allows to:

• detect and load the colortable upon ingestion (e.g. by rasimport)
• detect and write the colortable to the output, in particular encoding it in the output image when tiff is requested

Restored also priority since no alternative solution provided since months

[Piero Campalani]

Note: rasgeo keeps the table of color mappings of a categorical image directly in rasdaman (RASBASE), keeping a pointer to it petascopedb::ps_extra_metadata.

Solution B is to extend petascopedb to support SWE Category fields (now Quantities). This would be a backcompatible extension to the database.

[Peter Baumann]

Just for the records:
now that we support format parameters, aka

encode( a, "GTiff", "tag=value" )

we can advise rasdaman to put a colortable inside:
​http://www.awaresystems.be/imaging/tiff/tifftags/colormap.html

Admittedly, this does not solve the issue of how to determine a colortable - I am not sure, though, that this is the task of an array database in the first place.