Projection/Extent help

[Ed McNierney]

Camden -

Your EXTENT and UNITS need to be described in the units of the output
projection your map is using.  In your example below, everything is
fine.  But if you switch to the two commented EXTENT and UNITS lines, it
won't work unless your PROJECTION block is changed to have the map
generated in a different projection that uses those units.

Leave your EXTENT and UNITS alone, since you want to (I think) still
have your output projection be "latlong".  You need to create a new
PROJECTION block that's *inside* the LAYER definition block for the new
layer that's got units in feet.

By default MapServer assumes that all LAYERs not otherwise described are
in the same projection as the output projection of the image (the one
defined by the top-level PROJECTION block).  If that's not the case,
MapServer can't guess - you have to tell it that a given layer is in a
different projection by including a PROJECTION block inside that layer
definition.

What is the "other" projection?  You need to know either its name (if
it's a common, standard projection) or all the mathematical parameters
describing it if it's a custom projection.  If you don't know how to
describe it accurately, MapServer won't be able to guess for you <g>!

        - Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242 

-----Original Message-----
From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of Camden Daily
Sent: Thursday, December 16, 2004 11:30 AM
To: MAPSERVER-USERS at LISTS.UMN.EDU
Subject: [UMN_MAPSERVER-USERS] Projection/Extent help

Hello all.  I'm a mapserver newbie trying to figure something out.
Basically, I have two sets of shapefiles in different projections and
units.  One has units of dd, and one has units of feet.

When I combine the two, I'd like to define my extents for the whole .map
file using dd instead of feet.  I've made up a sample .map file where
I'm simply trying to display one layer with units of feet while defining
the extent using dd.  However, everything I try just gives me a blank
page.

If I define the extent in terms of feet and drop the "proj=latlong"
line, it shows up fine.  But I just can't get it to work when I define
the extent in dd.

Any help would be much appreciated!
-Camden Daily

MAP

  NAME Chicago
  STATUS ON
  DEBUG ON
  SIZE 300 300
  IMAGETYPE PNG
  IMAGECOLOR 240 240 240
  SHAPEPATH "/web_system/data"
  FONTSET "/web_system/fonts/fonts.list"
--------
  EXTENT -87.74 41.80 -87.56 41.98
  UNITS DD
  PROJECTION
    "proj=latlong"
  END
-------
  #EXTENT 1101584.450000 1841973.900000 1186739.850000 1969991.020000
  #UNITS FEET
-------
  WEB
    LOG "/web_system/logs/mapserver.log"
    IMAGEPATH "/web_system/tmp/"
    IMAGEURL "/tmp/"
  END

  LAYER
    NAME "cta_line"
    TYPE LINE
    STATUS DEFAULT
    DEBUG ON
    DATA "CTA_Line"
    CLASS
      COLOR 0 0 0
    END
    PROJECTION
       "init=epsg:26971"
    END
    UNITS FEET
  END

END