Subha..
You need to insert a EPSG:900913 description code in PROJ4 config
files and a row in spatial_ref_sys table in postgis DB. By default
PROJ4 has not a 900013 projection reference.
Try it!
Best regards
Rafael Soto
2008/8/20 Subha Ramakrishnan <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>>
Hi :
We are building a map based web portal using openlayers ,UMN
mapserver[5.0.2] and postgis DB.We use google as the base map
through openlayers.We need to overlay our custom layers from the
db on top of this base map, for that we are using Mapserver (is
run on a FC7 linux machine). It is observed that by default
openlayers converts google projection [900913] to EPSG:4326 when
the base map is fetched.
Now when we try to overlay an image that the mapserver generates,
there is a mismatch on the base map, though mapserver uses
epsg::4326. After searching over the internet theere seems to be
only one solution which is displaying the base map itself in
epsg:900913 and emit the mapserver image also in the same
projection. The problem is we are not able to generate an image
through mapserver in epsg::900913.
We have taken following measures untill now :
1> For using epsg:900913 projection in mapserver, we have added
following entry in the /usr/local/share/proj/epsg file.[proj
version 4.6]
"<900913> +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0
+x_0=0.0 +y_0=0 +k=1.0 +units=m [EMAIL PROTECTED] +no_defs <>" 2>
We have added following entry in the "in the spatial_ref_sys table
in postgis DB.
"900913 ,'EPSG',900913,'GEOGCS["WGS 84", DATUM["World Geodetic
System 1984", SPHEROID["WGS 84", 6378137.0,
298.257223563,AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich", 0.0,
AUTHORITY["EPSG","8901"]], UNIT["degree",0.017453292519943295],
AXIS["Longitude", EAST], AXIS["Latitude",
NORTH],AUTHORITY["EPSG","4326"]],
PROJECTION["Mercator_1SP"],PARAMETER["semi_minor", 6378137.0],
PARAMETER["latitude_of_origin",0.0], PARAMETER["central_meridian",
0.0], PARAMETER["scale_factor",1.0], PARAMETER["false_easting",
0.0], PARAMETER["false_northing", 0.0],UNIT["m", 1.0], AXIS["x",
EAST], AXIS["y", NORTH],AUTHORITY["EPSG","900913"]] |','+proj=merc
+a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0
+k=1.0 +units=m [EMAIL PROTECTED] +no_defs'); The mapfile is as
follows: (With this, We get a blank image without any exception.)
MAP
NAME MAP_POINTS
SIZE 725 800
IMAGETYPE PNG
EXTENT 6679169.446666667 -7.081154550627918 11131949.077777777
4865942.278825832
WEB
METADATA
wms_srs "EPSG:4326 EPSG:900913"
END
END
PROJECTION
"init=epsg:900913"
END
LAYER
CONNECTIONTYPE postgis
NAME indiastates
CONNECTION "user=postgres dbname=test host=localhost"
TYPE POINT
STATUS DEFAULT
#DATA "topology from states"
DATA "topology from india_states using unique id using SRID -1"
CLASS
COLOR 255 0 0
END
END
END
The client (openlayer) code is as follows :
options = {
projection: new OpenLayers.Projection("EPSG:900913"),
displayProjection: new OpenLayers.Projection("EPSG:4326"),
units: "m",
maxResolution: 156543.0339,
maxExtent: new OpenLayers.Bounds(-20037508, -20037508,
20037508, 20037508.34)
};
map = new OpenLayers.Map('map', options);
var gphy = new OpenLayers.Layer.Google("Google
Physical",{type: G_PHYSICAL_MAP,'sphericalMercator': true});
map.addLayers(gphy);
var lonLat = new OpenLayers.LonLat(82, 23) ;
lonLat.transform(map.displayProjection,map.getProjectionObject());
map.setCenter(lonLat,5);
var wms ;
wms = new OpenLayers.Layer.WMS( layername,
"http://localhost/cgi-bin/mapserv?";,
{ map: 'demo.map',
projection:"EPSG:900913",
transparent: 'true', layers: 'indiastates',
format: 'image/png'},{singleTile: 'true'} );
map.addLayer(twms1);
Can anyone help us in any way?
Also,
We have tried overlaying layer fetched from our map server
on different basemaps from (meta carta and tera pages) and have
found it overlays perfectly So clearly there is is problem
overlaying on google map through openlayers in epsg : 4326.
Thanks and sorry for the long mail.
Expecting a reply.
Subha.
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