[mapserver-users] Projection question

[Ian Walberg]

Steve,

Thanks for these details, I think I understand what you are saying.

I do need to experiment a little more to understand what we are seeing
however.

We do have a PROJECTION definition for each layer and the map block.

Regards

Ian

-----Original Message-----
From: mapserver-users-bounces at lists.osgeo.org
[mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Stephen
Woodbridge
Sent: Wednesday, August 31, 2011 9:33 PM
To: mapserver-users at lists.osgeo.org
Subject: Re: [mapserver-users] Projection question

Ian,

Projections are only done on the vertices of the objects. So the 4 
corners of the rectangle, which by the way should have a projection 
block, will get re-projected BUT then straight lines are drawn between 
the corners. If you want the rectangle edges to be reprojected with 
curvature, then you have to subdivide the edges into many points so the 
straight lines between the points give the appearance of curvature.

PROJECTION ... END blocks need to appear in two places.

in the MAP block the projection defines the output projection to use. If

a LAYER does NOT have a PROJECTION block then DATA for that layer is 
assumed to be in the output projection.

If the data for a LAYER is in some other projection then you need to 
have a PROJECTION block to define the LAYER's data projection.

-Steve W

On 9/1/2011 12:07 AM, Ian Walberg wrote:
> I thought I understood how PROJECTION worked in map files....
>
> The map file below renders the earth/countries outline and a rectangle
> with the overall map projection set to init=epsg:4326 and EXTENT -180
> -90 180 90.
>
> However when I change the overall map projection to "proj=ortho" and
> EXTENT -8000000 -8000000 8000000 8000000 I get a globe drawn the
> rectangle has not been projected onto the globe.
>
> I have various other layers with city names etc and all of these
project
> ok.
>
> What have I misunderstood here?
>
> Thanks
>
> Ian
>
> LAYER
>
> NAME "box"
>
> STATUS DEFAULT
>
> TYPE polygon
>
> FEATURE
>
> WKT "POLYGON ((180.0 0.0, -180.0 0.0, -180.0 90.0, 180.0 90.0, 180.0
0.0))"
>
> END
>
> CLASS
>
> STYLE
>
> COLOR 0 0 100
>
> END
>
> END
>
> PROJECTION
>
> "init=epsg:4326"
>
> END
>
> END
>
> LAYER
>
> NAME world
>
> TYPE polygon
>
> DATA World_Countries.shp
>
> STATUS DEFAULT
>
> CLASS
>
> STYLE
>
> COLOR 50 128 50
>
> OUTLINECOLOR 10 10 10
>
> WIDTH 1
>
> END
>
> END
>
> PROJECTION
>
> "init=epsg:4326"
>
> END
>
> END
>
> PROJECTION
>
> "init=epsg:4326"
>
> # "proj=ortho"
>
> # "lat_0=0.0"
>
> # "lon_0=-90.0"
>
> END
>
>
>
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> mapserver-users at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-users

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