[Proj] Shapefile and EXTENTS

[Chapman, Martin]

One more thing Matt.  You can hard code the parms to make your life easier like so:
 
static char* parms1[] = 
{ 
 "proj=poly",
 "lon_0=90W",
 "ellps=clrk80",
 "no_defs"
};
 
Martin

________________________________

From: proj-bounces at xserve.flids.com on behalf of Matthew Roberson
Sent: Tue 5/10/2005 8:00 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Shapefile and EXTENTS



Martin,

Thank you.  After reading your reply, I understand why I can't see my
map. Another question I have is, can I create a Lambert Azimuthal Equal
Area projection in Angular units using the proj utility? How would I do
that?  Thanks

Matt

On May 9, 2005, at 5:16 PM, Chapman, Martin wrote:

> Matt,
>
> 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.
>
> Martin
>
> -----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:
> (unknown)
> 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.
>
> Thanks,
>
> Matt
>
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