[mapserver-users] projections [shpmidx] [shpmidy]

[Marco]

Hi list,

If the next question is a stupid one, excuse me. I am newbe.

context:

I use mapserv CGI (no mapscript) and a Apache webserver with PHP (on a windows machine for testing). I am building a web-application with dynamic maps. 

problem:

I use a template file to get information about the map-features on the current map. The tags [shpmidx] and [shpmidy] provides information on the exact position of a feature (see http://mapserver.gis.umn.edu/doc36/template-reference.html ).

With simple lineair algebra it is possible to calculate the xy-position of this feature on the actual generated image. (a lineair transformation from "real world" lat-lon coordinates to "image" x-y pixelcoordinates).
I use these information to create some kind of javascript rollover interface; if the mouse hovers a feature, the webapplication respons immediately, without the need of connecting to the server.

So far so good. Everything works fine. So now for the problem. If I deploy a projection ("proj=stere") Nothing works anymore. That is because [shpmidx] and [shpmidy] gives the lon-lat stuff, but i need the xy coordanates on the generated image of the map. Sure it should be possible to write transformations for projected maps (a lot of sinus and cosinus, arctangens etcetera i suppose) but i believe that's a ticket to the nearest snake pit.

Is there a solution for this (withhout the need of writing my own transformation formulas)

Or, if I have to write transformation, does anybody now the formulas for this projection:

PROJECTION

"proj=stere"

"lat_0=52.156160556"

"lon_0=5.387638889"

"k=0.0000999908"

"x_0=0.000"

"y_0=0.000"

"ellps=bessel"

END




Cheers,

Marco




Marco Pieck, marco at mediaeval.nl
Mediaeval Vorm & Visie
http://www.mediaeval.nl/
postbus 1050, 6501 BB  Nijmegen,  the Netherlands 
tel: ++ 31 24-3818196, fax: ++ 31 24-3818183

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