Change Projection on-the-fly; Using PostGIS - How?

[Julien-Samuel Lacroix]

Hi,
You'll have to set the projection of all your layers in the mapfile. 
This why changing the projection of the map object won't affect them. 
Then you'll be able to use:
$map->setProjection("proj=robin,lon_0=0,x_0=0,y_0=0", MS_TRUE);

For the PostGIS SRID, you don't have to change anything if you set the 
PROJECTION in your layer.

Julien


Brent Wood wrote:
> --- Stefan Schwarzer <stefan.schwarzer at GRID.UNEP.CH> wrote:
> 
> 
>>Hi there,
>>
>>i am struggling since quite a while to set-up a change-projection-on- 
>>the-fly possibility for our website mapserver. But somehow, I don't  
>>really have the clue how to do it. Now, making things "worse" (more  
>>complicated for me) we have migrated from MySql to Postgres/Postgis.
>>
>>------------------------------------------------------------------------ 
>>----
> 
> 
> 
> At least your spatial queries now have a chance of returning correct answers
> :-)
> 
> The way I prefer to do this is to have the SQL thrown at Postgis do the
> conversion, so mapserver doesn't have to. Thus:
>   select transform(the_geom, SRID) 
> instead of 
>   select the_geom
> 
> But that's probably just because I have a SQL/database background, so tend to
> do my work there. But it saves the wrestling with mapscript that you're going
> through :-)  
> 
> 
> Cheers,
> 
>    Brent Wood
> 
> 
>>So, first question would be: What code to use to change the  
>>projection via PHP/Mapscript, should be something like this, I guess:
>>
>>$newproj=ms_newprojectionObj("proj=robin,lon_0=0,x_0=0,y_0=0");
>>$latlon=ms_newprojectionObj("+proj=longlat +ellps=WGS84 +datum=WGS84 
>>+no_defs");
>>$oldext=ms_newRectObj();
>>$oldext->setextent(-180,-90,180,90);  //this is the extent of my map  
>>in geographic
>>$oldext->project($latlon,$newproj);  //reproject to Robinson
>>$map->setextent($oldext->minx,$oldext->miny,$oldext->maxx,$oldext- 
>> >maxy);  //set the new map extent
>>
>>But I guess, something is still missing... (What about $map- 
>> >setProjection ?)
>>
>>------------------------------------------------------------------------ 
>>----
>>
>>And the second question is: As my mapfile queries the postgis  
>>database, using "SRID", I guess I need to change that one too, then?  
>>Instead of 4326 for Geographic I would have to use the one for  
>>Robinson (or Mollweide or so) ??
>>
>>------------------------------------------------------------------------ 
>>----
>>
>>Thanks for giving me any hints...
>>
>>Stef
>>

-- 
Julien-Samuel Lacroix
Mapgears
http://www.mapgears.com/