map projection question from a newbie

[James Washer]

So, are you saying that mapserver will show a degree of latitude and a degree on longitude on the screen the SAME NUMBER of pixels wide no matter what the latitude (unless there is some overiding projection directive)?

On Thu, 22 Sep 2005 08:09:10 -0400
Stephen Woodbridge <woodbri at SWOODBRIDGE.COM> wrote:

> Hi James,
> 
> You are doing nothing wrong. Mapserver takes the coordinate in the file 
> and treats them as X/Y and generates the images based on this. If you 
> plot geographic long/lat as X/Y you get an elongated image. xastir must 
> be compensating for the fact that it is geographic data and applying a 
> hidden projection of some type.
> 
> Mapserver does not do this. if you want it projected you have to 
> EXPLICITLY tell it to perform a projection.
> 
> In the mapfile, you can define the OUTPUT projection in the MAP object 
> and the projection that the data is in in the LAYER object, or you can 
> leave all the PROJECT ... END blocks out if they are all the same and it 
> will just plot the data as X/Y.
> 
> -Steve W.
> 
> James Washer wrote:
> > I'm a newbie to mapping in general, so please have mercy if I'm asking stupid questions.
> > 
> > I have a shapefile that was given to me in Nevada State Plane, and I used shpproj to reproject as follows:
> >  shpproj stateplane_shapefile geographic_shapefile -i="init=nad83:2703 units=us-ft" -o=geographic
> > 
> > The map looks perfect when I view it in xastir (ham radio APRS mapping program) but looks about 30% too wide when viewed with mapserver.
> > 
> > Here's the map file... Any ideas what I'm doing wrong?
> > 
> > thanks for reading this far.
> > 
> >  - jim
> > 
> > MAP
> > 	IMAGETYPE      PNG
> > 	#EXTENT	-119.961409 38.535114 -119.310436 39.113979
> > 	EXTENT	-120.0 38.535114 -119.25 39.113979
> > 
> > 	SIZE           600 600
> > 	SHAPEPATH      "/usr/local/share/xastir/maps/Douglas/Parcels"
> > 	#SHAPEPATH      "/var/www/html/gis/Douglas/Parcels"
> > 	IMAGECOLOR     200 200 200
> > 
> > 	WEB
> > 		TEMPLATE doug2-1.html
> > 		IMAGEPATH "/var/www/html/gis/tmp/"
> > 		IMAGEURL "/gis/tmp/"
> > 	END
> > 	
> > 	LEGEND
> > 		STATUS EMBED
> > 		POSITION LR
> > 		#TRANSPARENT TRUE
> > 	END
> > 
> > 	UNITS DD
> > 
> > 
> >        PROJECTION
> >                 "proj=latlong"
> >                 "ellps=WGS84"
> >        END
> > 
> > 
> > 
> > 	SCALEBAR
> > 		STATUS EMBED
> > 		UNITS MILES
> > 		INTERVALS 3
> > 		OUTLINECOLOR 0 0 0
> > 	END
> > 
> > 	LAYER # States polygon layer begins here
> > 		NAME         Parcels
> > 		DATA         dc_pcls1
> > 		STATUS       DEFAULT
> > 		TYPE         POLYGON
> > 		LABELITEM	TAG
> > 		#CLASS
> > 			#NAME	"TAG"
> > 			#EXPRESSION 
> > 
> > 		CLASS
> > 			NAME       "Douglas County Parcels"
> > 			STYLE
> > 				COLOR        232 232 232
> > 				OUTLINECOLOR 32 32 32
> > 			END
> > 			LABEL
> > 				SIZE LARGE
> > 				MINFEATURESIZE 200
> > 			END
> > 		END
> > 	END
> > 
> > END
> >