[mapserver-dev] Development of new functions "combine symbols" and "displace symbols"

[Tamas Szekeres]

Hi Olaf,

Please find my comments inline below:

2011/1/25 Olaf Knopp <olaf.knopp at wheregroup.com>

> 1. I would prefer a centroid.
> 2. I think it should be possible to click on the combined symbol and get a
> featureInfo of all combined objects. Perhaps this is not useful if you have
> many symbols. What do you think?
>

It would require a bit more time to consider all aspects but by looking at
the example you mentioned it seems that a new feature should be created for
each cluster on the fly and some aggregated attributes (like the number of
the features attached to this cluster) should also be added to these new
features.  The features of this layer should be cached up during the cluster
generation and  each combined features should be assigned with a separate
class during the rendering phase. The feature query may probably work as it
stands now and provide only the primary features in the result set. BTW: I
didn't find the query option to work in the example site you mentioned.



>
> Displace Symbols:
> 1. It should be possible to configure each layer (PRIORITY, DISTANCE of the
> relocation and a displace ANGLE) to avoid the relocated symbols cover each
> other.
> 2. Yes this is a problem. I think we can't solve it, because it could
> create a "cascade" in the mapfile with every symbol relocated. Perhaps we
> should limit the function only to objects with the same coordinates. You
> will then have to configure the mapfile and layers to provide the best map
> design.
>

This option requires the features of more than one layer to be negotiated,
currently the label cache is working this way, it would be nice to fit this
process into the existing framework if possible.


>
> values of COMBINEUNITS and DISPLACEUNITS?: I think it would be best to use
> the options that are mostly availible in MapServer:
> [pixels|feet|inches|kilometers|meters|miles|nauticalmiles], but to make the
> configurement easy pixels is the option of choice, because you can "play"
> with symbolsize and the displacedistance.
>
>
I could imagine only pixels or some other units (like points or twips, not
normally used in MapServer) which may also be related to screen coordinates.
The distance of the features in map coordinates doesn't change when
modifying the scale or zoom of the map. I would also think that this option
should be switched off when the scale dependent rendering of the symbols is
used (ie symbolscale) for that layer.



> By the way. Do you know how this would work? Do we have to give a concept
> to the steering commitee e.g. for the options like "COMBINEUNITS,
> DISPLACEUNITS, COMBINESYMBOLS" etc? Do you commit to the MapServer trunk?
>
>
Yes, an RFC describing all the related changes would be required, the
technical details are discussed on the -dev list. In most cases the
developer implementing the feature provides the RFC and commits the
implementation if approved. You may count me as a potential candidate to
take part in these efforts.


Best regards,

Tamas
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