Richard Greenwood wrote:
On Tue, Jul 14, 2009 at 11:27 AM, Andy Colson <[email protected]
<mailto:[email protected]>> wrote:
Hi all,
I'm working on my first mapping project, so IANAM (I am no a
mapper). Here is the projection info from a shapefile I'm using:
PROJCS["NAD_1983_StatePlane_Iowa_North_FIPS_1401_Feet",
GEOGCS["GCS_North_American_1983",
DATUM["D_North_American_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.017453292519943295]],
PROJECTION["Lambert_Conformal_Conic"],
PARAMETER["False_Easting",4921250.0],
PARAMETER["False_Northing",3280833.333333333],
PARAMETER["Central_Meridian",-93.5],
PARAMETER["Standard_Parallel_1",42.06666666666667],
PARAMETER["Standard_Parallel_2",43.26666666666667],
PARAMETER["Latitude_Of_Origin",41.5],
UNIT["Foot_US",0.30480060960121924],
PARAMETER["scale_factor",1.0]]
I used QGIS to create a mapfile, and it generated this:
PROJECTION
'proj=longlat'
'ellps=WGS84'
'datum=WGS84'
'no_defs'
''
END
I was kind of thinking this (Thanks to FrankW for helping me find
the right epsg code):
PROJECTION
'init=epsg:3417'
END
Is the first one even right?
No
Would there be a difference?
The first one is spherical, but State Plane is Cartesian (on a plane).
Why might I choose one over the other? I'm going to put this into
postgis, with srid = 3417, will that make any difference.
Yes.
(I'd like to avoid re-projections.. I think... don't I?)
Reprojection isn't evil. You may as well do it right, but the main thing
with postgis is that you put it in, and take it out, calling the same
projection. Which could be -1 if you really don't know/care. MapServer
doesn't set a layer's projection from postgis. If you have a layer(s)
that's different from the map's overall projection, then you'd need to
set the projection in the layer definition, not necessarily in postgis.
Setting a layer's projection different from the map's projection is what
will trigger reprojection.
HTH,
--
Richard Greenwood
[email protected] <mailto:[email protected]>
www.greenwoodmap.com <http://www.greenwoodmap.com>
Ahh, so QGIS didn't export a projection that matched my data. (I assume
its a default that it always exports...)
> The first one is spherical, but State Plane is Cartesian (on a plane).
Heh.. that's one of those answers that brings up more questions. But
google is helping me out.
Thanks for the help,
-Andy
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