[Proj] Shapefile and EXTENTS

Chapman, Martin MChapman at sanz.com
Mon May 9 18:16:46 EDT 2005


The issue is that you are converting from angular units to linear units
when projecting from geographic to a projected system.  Angular units
range from -180 to 180 and 90 to -90 degrees.  After the re-projection
your values are in false easting and false northing which are huge
number offsets to put all values in the positive quadrant of the
cartesian plane.  If you are trying to display linear units in a map
configured to show angular units, then your linear units will be way off
the screen.  Make sure your map is rendering in the same spatial
reference system as the file you are trying to display, or vice-versa.


-----Original Message-----
From: proj-bounces at xserve.flids.com
[mailto:proj-bounces at xserve.flids.com] On Behalf Of Matthew Roberson
Sent: Monday, May 09, 2005 3:43 PM
To: proj at xserve.flids.com
Subject: [Proj] Shapefile and EXTENTS

I am trying to do a project a map of the state of Missouri that was 
created by the US Census Bureau(zt29_d00.shp).

I used ogrinfo to get the following information about the EXTENT:

[imac-dev03:~/Documents] matthewr% ogrinfo -so zt29_d00.shp zt29_d00
INFO: Open of `zt29_d00.shp'
using driver `ESRI Shapefile' successful.

Layer name: zt29_d00
Geometry: Polygon
Feature Count: 1341
Extent: (-95.774704, 35.995683) - (-89.098843, 40.613640)
Layer SRS WKT:
AREA: Real (20.5)
PERIMETER: Real (20.5)
ZT29_D00_: Integer (11.0)
ZT29_D00_I: Integer (11.0)
ZCTA: String (5.0)
NAME: String (90.0)
LSAD: String (2.0)
LSAD_TRANS: String (50.0)

Then, I used proj4 to find lat long values for the a Lambert Azimuthal 
Equal Area projection.

[imac-dev03:~/Documents] matthewr% proj +proj=laea +ellps=clrk66 +R_A
-95.774704 35.995683
-7567149.62     5525023.18
-89.098843 40.613640
-6798293.00     5830370.88

When I use these values with MapServer to make a map, nothing shows up. 
  Am I missing something.  Should I post this question in this list or 
in the MapServer User's group? Any help would be appreciated.



Proj mailing list
Proj at xserve.flids.com http://xserve.flids.com/mailman/listinfo/proj

More information about the Proj mailing list