Add color legend support to ktile raster layer

[matthewma7]

And some code refactoring

[manthey]

Should there be a legend even when the colors aren't custom? Also, it seems like there should be a way to modify the default -- for instance, if I want a black-to-white continuous scale with different min and max values.

[aashish24]

@matthewma7 do you have an answer for @manthey's question above?

[matthewma7]

@aashish24 I meant to ask @dorukozturk when I got a chance. I guess I can ask him now. Hi @dorukozturk, I don't you may not know the answer fully, but since you have more experience with Mapnik than I do, I am wondering that is the default Mapnik render behavior without style predictable? I mean, when there are three bands, it will be rendered to color. When there is, in this case, one band, does it always use the same greyscale? Is the greyscale ordinal or continuous?

[dorukozturk]

@matthewma7 Here they list bunch of options. I think your options are

• mapnik2.COLORIZER_LINEAR
• mapnik2.COLORIZER_DISCRETE
• mapnik2.COLORIZER_EXACT
• mapnik2.COLORIZER_INHERIT

"The colorizer also has default color, which input values will be converted to if they don't match any stops. The colorizer also has a default mode, which can be inherited by the stops." From the docs.

[aashish24]

When there is, in this case, one band, does it always use the same greyscale? Is the greyscale ordinal or continuous

greyscale is assumed when there is only one band. You can look into QGIS which is the industry standard tool.

greyscale would be continuous (think of height map)

[matthewma7]

After a discussion with @aashish24, we decided to implement legend for default raster styling in the separate PR, because it might involve something with some complexity outside the current changes. An issue has been created for that request, https://github.com/Kitware/minerva/issues/459

[aashish24]

LGTM if @manthey also approves it.