[mapserver-users] Nationalatlas Shapefile Projection

[Ed McNierney]

Sure - just use PROJ, the projection tool MapServer uses (available from
http://www.remotesensing.org/proj).  The "four corners" technique is a
good start, but please remember that it won't always ensure that the
entire original area is visible in the output area.  But it's usually
fine and you can tweak things from there.

	- Ed

Ed McNierney
Chief Mapmaker
TopoZone.com
ed at topozone.com
(978) 251-4242


-----Original Message-----
From: Stephen Woodbridge [mailto:woodbri at swoodbridge.com]
Sent: Friday, March 22, 2002 8:22 AM
To: Ed McNierney
Cc: Sathiskumar Govindasamy; mapserver-users at lists.gis.umn.edu
Subject: Re: [mapserver-users] Nationalatlas Shapefile Projection


OK, so is there a utility that lets you say project the extents so you
have new numbers for you map file? You would probably want to project
all four corners of your extents and then take the exnts of the
projected corners to be you new extents in the project space.

-Steve

Ed McNierney wrote:
> 
> 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