[Mapserver-users] Symbology Questions (Charts)

[Geoghegan, Sean]

Hi,

I have a couple questions about symbols, firstly, the easy one: The Mapfile reference says "The symbol name or number to use for all features if attribute tables are not used." Can someone explain what this means and how do you use attribute tables and what difference do they make with the rendering of symbols?

Secondly, I am looking at making a symbol which is a dynamically generated chart based on attributes.  Has anyone looked at doing that?  The way I see it, there are a couple possible way of doing this, firstly a new symbol type could be added to MapServer which generates charts based on a features attributes.  This would be faster since it would be all done by mapserver itself however it might require extensive changes to the mapfile format to allow for passing of attributes to the chart generation routine and it could limit the way attribute could be retrieved, for example I might want to chart attributes for a feature that are stored in more than one row in a separate database.

The alternative is to do this in mapscript and provide a service that renders a single transparent layer with the charts, generated by other means, as symbols.  This would be a bit slower and require an extra request, however it would probably be easier to implement.

Can anyone offer any recommendations regarding this?  Personally I am a bit relucant to make such large changes to MapServer and particularly to the mapfile format.

Thanks in advance.

Sean Geoghegan
Command and Intelligence Environments Branch
Command and Control Division
Defence Science and Technology Organisation
sean.geoghegan at dsto.defence.gov.au