[mapserver-users] Nationalatlas Shapefile Projection

[Ed McNierney]

Sathis -
 
Your EXTENT numbers are in the same units your output projection is in.
If you're displaying decimal degrees, the extents work.  When you
project the output to LCC, the units change completely, and the EXTENT
numbers now specify a tiny little area that's nowhere near the United
States.  That's why you get a blank image.
 
    - Ed
Ed McNierney 
Chief Mapmaker 
TopoZone.com 

-----Original Message-----
From: Sathiskumar Govindasamy [mailto:gsathis at yahoo.com]
Sent: Thursday, March 21, 2002 9:26 PM
To: mapserver-users at lists.gis.umn.edu
Subject: Re: [mapserver-users] Nationalatlas Shapefile Projection


Hi all,

To give a better idea about what I am trying to acheive, I have
explained little bit more in this mail than before. I wanted the
mapserver to generate the image of USA in the "lcc : Lambert Conformal
Conic projection" or "aea : Albers Equal Area" or which ever suits best
for US. I have the National Atlas US States shapefile statesp020.xxx .
The following is the map file.

NAME USA 
STATUS ON 
EXTENT -126 50 -66 24 
UNITS METERS 
SIZE 700 550 
SHAPEPATH "data" 
IMAGECOLOR 79 173 253

PROJECTION 
        "proj=lcc" 
        "lat_0=24" 
        "lat_1=50" 
        "lon_0=-99" 
END

WEB 
        TEMPLATE demo.html 
        LOG demo.log 
END

# 
# Start of symbol definitions (we're only using a few) 
# 
SYMBOL 
        NAME 'circle' 
        TYPE ELLIPSE 
        POINTS 1 1 END 
        FILLED TRUE 
END

# 
# Start of layer definitions 
#
LAYER 
        NAME statesp020 
        MAXSCALE 600000 
        TYPE POLYGON 
        STATUS DEFAULT 
        DATA statesp020 
        PROJECTION 
                "proj=latlong" 
                "ellps=clrk66" 
        END

        CLASSITEM 'state' 
        CLASS 
                NAME 'Unwanted States' 
                EXPRESSION /'Virgin Island'|Puerto|Alaska/ 
                OUTLINECOLOR 198 243 255 
                COLOR 198 243 255 
        END 
        CLASS 
                NAME 'State & Nation Boundary' 
                EXPRESSION /./ 
                OUTLINECOLOR 180 180 180 
                COLOR 255 255 255 
                OVERLAYSYMBOL 'circle' 
                OVERLAYSIZE 2 
                OVERLAYOUTLINECOLOR 180 180 180 
        END

        TOLERANCE 0 
END

END

In the Map PROJECTION Section when I change the above shown on to
proj=latlong and remove lat_0 and other stuff, then the map shows up
correctly. But, when I have it as shown above, I just only see an image
with solid image color. Can someone tell me where I am making mistake ?

Thanks 
Sathis

Kieran J. Ames wrote:

Sathis, 
I'll share the little I know with you. 
You need to investigate projections in general. Different projections
render 
maps in different ways. If you have ArcView (what I use), you can take
your 
UNPROJECTED DATA (Decimal Degrees) and PROJECT it. This will allow you
to see 
what happens. If you can't do that, then you might post to the group and
ask 
them what the best projection for this would be. 
eg: if you want to show North America and NOT zoom in, you may choose
one 
projection over another. Tell the group what you want to accomplish and
go from 
there. 
HTH. 
Kieran