Raster image doesn't show

[Ed McNierney]

Dan -
 
If you are going to mix different projections in a mapfile, you need to
tell MapServer what's going on.  It looks like you have a good
PROJECTION description for your input raster layer, and you seem to want
the same output projection used in the map image itself.  That's fine.
But you are now creating a point layer with a DIFFERENT projection, but
you're not doing anything that would let MapServer know that.
 
You need three PROJECTION blocks - one at the top level (just below the
EXTENT and UNITS is fine) to tell MapServer what output projection
you're using (the stereographic one you've defined below).  And you need
that same PROJECTION block in the raster layer to tell MapServer that
that's the input projection for that layer.  And you then need a third
one in the point layer to tell MapServer that the coordinates you're
using for that layer are NOT in the stereographic projection but are in
lat/lon degrees.  That is, a block like:
 
PROJECTION
   "proj=latlong"
   "datum=WGS84'
END
 
Then MapServer will know that it needs to reproject that input
projection to the same output projection used in the output image.
 
    - 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 

________________________________

From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of d c
Sent: Friday, May 05, 2006 10:44 AM
To: MAPSERVER-USERS at LISTS.UMN.EDU
Subject: Re: [UMN_MAPSERVER-USERS] Raster image doesn't show


Ed,

This is the extent of my map: 

EXTENT -3174450 -2816050 2867175 2406325
UNITS METERS

I'm trying to display a point element on a geotiff raster file, as
follows (Note the decimal degree format):

LAYER 
    TYPE POINT
    STATUS DEFAULT
      FEATURE
        POINTS 
            56.5333333 -71.5  #  <------- DD
        END
        TEXT "HELLO WORLD"
    END
    CLASS
        COLOR 255 0 0 
        SYMBOL 'cross'
        LABEL
            TYPE bitmap
        END
    END
    TOLERANCE 5
END

The label, according to the coordinates given, sometimes appears,
sometimes does not and most often 
on the same (erroneous) spot. 

I tried to change the EXTENT (and UNITS) to decimal degrees according to
the output of gdalinfo which outputs corner coordinates both in meters
and decimal degrees. I thought I could this way make Mapserver
understand I was specifying the input in decimal degrees so it should
output correctly the point I want to draw. The scalebar also revealed
seriously confused. 

I did not mention that the map is of Antarctica. This apparently
complicates the matter since the EXTENT values are different than on
most maps. 

I'm new to this so I haven't got much knowledge about projections. The
following two I have used successfully in displaying the map (but not
the point): 

PROJECTION
 "proj=stere"
 "ellps=WGS84"
 "datum=WGS84"
 "lon_0=0"
 "lat_0=-90"
 "lat_ts=-71"
 "units=m"
END

PROJECTION 
  "init=esri:102021"
END

Thanks for your help,

Dan



2006/5/5, Ed McNierney <ed at topozone.com>: 

	D C -
	 
	The UNITS and EXTENT in your mapfile need to correspond to the
units used in the projection of your data.  If they don't, then you're
looking to reproject the data and there's some extra work you need to
do.
	 
	gdalinfo will tell you the units and extent in the data source's
native projection.  Changing those values in the mapfile won't change
the input data, and you're simply requesting an output image that
doesn't correspond to any part of your input data, so you (correctly)
get nothing displayed.
	 
	What is it you're trying to do?  Are you trying to display the
image in a different projection than the raster source image is using?
If so, what projection does the raster use and what output projection do
you want?
	 
	    - 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 


________________________________

	From: UMN MapServer Users List
[mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of d c
	Sent: Friday, May 05, 2006 5:54 AM
	To: MAPSERVER-USERS at LISTS.UMN.EDU
	Subject: [UMN_MAPSERVER-USERS] Raster image doesn't show
	
	
	
	Hello,
	
	I just changed the EXTENT of my mapfile which was in METERS to
DD.
	I just wrote down the corresponding decimals which were given by
gdalinfo.
	
	BEFORE
	--------------
	UNITS METERS
	EXTENT -3174450 -3225675 2867175 2815950 
	
	
	AFTER
	-----------
	
	UNITS DD
	EXTENT  -131.5 -56.5 134 -52.3
	
	nb: the map is a raster im. of antarctica
	
	The PROBLEM now is that THE MAP DOESN'T SHOW.
	I don't get an error or anything, the map just doesn't show. 
	
	Any suggestions? 
	
	Thanks in advance. 
	


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