[mapserver-dev] spatial restriction for queries / ms-rfc-22a

[Tamas Szekeres]

2009/10/9 Martin Kofahl <M.Kofahl at gmx.net>

> Hi Tamas,
> this is a very interesting rfc. I'm still reading through your patches in
> order to follow the examples as I haven't heard of vtables yet. Can you
> please clarify some things for me?
>
> - Any filterings are probably done in mapfilter.c, currently for
> MS_SHAPE_POINT/LINE/POLYGON. Does this has to be extended for all other
> types including raster?
>
>
Martin,

The concept of RFC22  (http://mapserver.org/development/rfc/ms-rfc-22a.html)
is related only to the 'data source' vtable, and we could only filter vector
data (ie. shapes) by using this approach. With regards to the raster data
this could provide an option only to filter the tiles by the tile indexes
(when using tiled rasters).

If you're about to exclude arbitrary regions then you should probably plug
in to the renderer vtable (rendererVTable) which is a pretty new concept in
MapServer. I could imagine an intermediary renderer which would be capable
to modify the image rendered by another renderer. However this option is not
covered by RFC22 at all.



> - There's a mail on the list saying that performance is quite slow. Have
> you done any measurements?
>
>
I'm not aware of much issues with the performance of this concept itself. I
guess you're pointing to the performance issue of the 2-phase query
behaviour of MapServer which would be one of the issues addressed by RFC22.
I must mention that this problem has already been addressed by MapServer in
another way (see: http://mapserver.org/development/rfc/ms-rfc-52.html)

- There's no vote on this rfc. Does it make sense to work on it, so how are
> the chances that your concept will go into the development version.
>
>
Every significant change would normally require an RFC and should be
approved by the MapServer PSC in a voting process. I would normally prefer
to issue a vote if I had at least some of the PSC members support the
concept, but it seems this one has lack of this support due to the presumed
complexity of these additions, which would be considered to violate the
designated objective of "MapServer is not a full-featured GIS system, nor
does it aspire to be."  (http://mapserver.org/)



> - Can you give an abstract of work which is to be done?
>
>
I think we should normally require:

1. An RFC to describe the required changes to satisfy with your needs to be
able to discuss on
2. The RFC should be negotiated on the mapserver-dev list
3. Issue a vote on the RFC
4. If the voting is passed then implement the changes and modify the doc
accordingly


I currently don't have enough motivation to proceed with this RFC, as
currently I have no such requirements in my project actually. However I
would still support having such feature in MapServer (it should probably be
extended to the renderer vtables as well) if someone would feel enough power
to do some polishing on that.


Best regards,

Tamas
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