There is normally a constraint set on postgis tables that specifies
the SRID, if you want to change the SRID then you need to drop the
constraint, set the SRID and optionally put back the constraint with
the correct SRID.
I do not believe this is necessary to achieve what you want, though.
An SRID of -1 tells postgis to return the geometry as is to
mapserver. Mapserver then doesn't know what the projection of the
data is, but that is okay because you can provide an PROJECTION object
on your layer in mapserver. Then mapserver knows what the projection
of the data is without having to consult postgis and will be able to
reproject the data for you.
So you should be able to leave your data in the database with SRID -1
and put
PROJECTION
"init=epsg:26915"
END
in your layer. Then if you use a different projection at the MAP
level, mapserver knows that your data is in UTM zone 15 and will
reproject it on the fly.
If you are *always* going to reprojecting your data then you should
actually transform it in the database so that you don't suffer from
reprojection overhead on every request.
Cheers
Paul
On 28-Jun-08, at 2:12 AM, [EMAIL PROTECTED] wrote:
Hi Matthew,
If you loaded it from shapefiles using shp2pgsql, then use the -s
flag to set the srid to the correct value.
If you \d your table, I think you'll find a constraint on it setting
the srid, as well as the geometrycolumns entry.
The simplest way to get things working with mapserver may well be to
leave it as -1 in the database (& geometrycolumns entry) & in your
mapserver mapfile data statement, specify the sql returns
setsrid(geom,26915) instead of geom, so postgis returns the values
with the appropriate SRID set, irrespective of what the database
actually stores.
That will get things working until you load the data with the
correct srid.
HTH,
Brent Wood
--- On Sat, 6/28/08, Matthew Pettis <[EMAIL PROTECTED]> wrote:
From: Matthew Pettis <[EMAIL PROTECTED]>
Subject: [mapserver-users] Basic Projection Help
To: "Mapserver-users" <[email protected]>
Date: Saturday, June 28, 2008, 5:47 PM
Hello,
I'm trying to get a handle on projections and
reprojections. I have a
dataset in a postgis database table that is in epsg:26915
(it's the state of
MN). I know this from the metadata provided by the
provider (state of
Minnesota itself).
When I loaded it into postgis, the geometry_columns row for
this
table/column combo set srid=-1. As I know that this is in
epsg:26915, I
manually changed the geometry_columns row entry to it (see:
===
geometry_columns === section).
Problem is, I get an error of using two different
geometries. Anybody have
any idea how i set the srid to the correct value of
epsg:26915? I'd like to
set this correctly so I can reproject it as necessary. The
map will render
with srid=-1, but then I don't think I can reproject
the image correctly,
right?
below are what I think are the important sections to this
problem. Thanks
in advance for your help.
Matt
=== url ===
=
=====================================================================
http://localhost/cgi-bin/mapserv.exe?map=C:\ms4w\Apache\htdocs\ol
\mapreproj.map&mode=map
=
=====================================================================
=== error message ===
=
=====================================================================
msDrawMap(): Image handling error. Failed to draw layer
named 'state'.
msPOSTGISLayerWhichShapes(): Query error. Error executing
POSTGIS SQL
statement (in FETCH ALL): DECLARE mycursor BINARY CURSOR
FOR SELECT
asbinary(force_collection(force_2d(the_geom)),'NDR'),gid::text
from
shp_state WHERE the_geom &&
setSRID('BOX3D(141095.125 4809728.25,810342.625
5478975.75)'::BOX3D,
find_srid('','shp_state','the_geom')
) -ERROR:
Operation on two geometries with different SRIDs
=
=====================================================================
=== geometry_columns ===
=
=====================================================================
oid
;f_table_catalog
;f_table_schema
;f_table_name;f_geometry_column;coor_dimension;srid;type
336791;"''";"public";"shp_state";"the_geom";2;26915;"MULTIPOLYGON"
=
=====================================================================
=== mapreproj.map ===
=
=====================================================================
MAP
################
# Map attributes
################
IMAGETYPE PNG
EXTENT 184056.505 4809728.25 767381.245 5478975.75
SIZE 600 600
IMAGECOLOR 255 255 255
FONTSET
"C:/ms4w/Apache/htdocs/fonts/fonts.list"
####################
# Web settings
####################
WEB
IMAGEPATH "C:/ms4w/Apache/htdocs/tmp/"
IMAGEURL "/tmp/"
END
####################
# State
# Background shows through missing precincts to show
where no votes will
be coming from
####################
LAYER
NAME "state"
CONNECTIONTYPE postgis
CONNECTION "user=postgres dbname=gisvote
password=postgres"
DATA "the_geom from shp_state"
STATUS default
TYPE polygon
CLASS
NAME "state"
COLOR 200 200 200
END
END # Layer state
END
=
=====================================================================
--
It is from the wellspring of our despair and the places
that we are broken
that we come to repair the world.
-- Murray
Waas_______________________________________________
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__________________________________________
Paul Spencer
Chief Technology Officer
DM Solutions Group Inc
http://www.dmsolutions.ca/
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