Call for comments -RFC 39

[Daniel Morissette]

Yewondwossen Assefa wrote:
> Bart van den Eijnden wrote:
>> Basically I feel the need for a higher object, something like THEME or
>> CLASSIFICATION which groups together a set of classes. This would also
>> make it easier to re-use blocks of classes between several layers
>> without having to copy/paste them. But I can understand if this is
>> outside of the scope of this RFC :-)
>>
>  I agree with this, I think this is what Steve raised too and I hope I 
> mostly answered to this in that e-mail.
> 
> 

Guys,

Sorry for being late to the game... hopefully it's not too late.

What bugged me initially was the use of text strings as class group 
names and the fact that we'd need to do string comparisons to match 
class group names for every class evaluation when rendering... leading 
to a guaranteed performance hit unless we do something to cache the 
results of the string comparisons.

I am also (like Bart) trying to find a way that we could add a higher 
level object to group classes instead of using text tags inside the 
current classes. That new level of object would correspond to SLD Styles 
but since the keyword STYLE is already used for something else in 
MapServer we cannot use it here. I was looking for a name for this new 
beast and could not find one... until I read Bart's THEME idea... I 
think this may be what we need.

Here is an example of what I'm thinking, adapting your RFC-29 example to 
use the THEME concept:

LAYER
  ...
  USETHEME "group1"
  ...
  THEME
    NAME "group1"
    CLASS
      NAME "name1"
      ...
    END
    CLASS
      NAME "name3"
      ...
    END
  END
  THEME
    NAME "group2"
    CLASS
      NAME "name2"
      ...
    END
  END
  ...


For the time being, classes defined at the top-level of a layer (i.e. 
not part of a THEME block) would be part of the "default" theme... this 
way old mapfiles continue to work.

Then the day we want to implement the concept of "style table"... err... 
I mean "theme table" at the mapfile level, we would allow the definition 
of THEMES at the top level in a map, or in an external THEMESET file to 
be consistent with SYMBOLSET/FONTSET terminology.

Just some late Friday afternoon thinking... I'm really not sure we got 
all bases covered... and this definitely does not map perfectly to the 
RST concept that I and Assefa used to work with in a previous life, but 
at least that would be closer.

Daniel
-- 
Daniel Morissette
http://www.mapgears.com/