GetMap - WMS 1.1.1 vs 1.3.0

Question

This works: http://mrdata.usgs.gov/services/sc?REQUEST=GetMap&SERVICE=WMS&VERSION=1.1.1&WIDTH=256&HEIGHT=256&FORMAT=image/png&BBOX=-83.4,32,-78.4,35.3&LAYERS=South_Carolina_Lithology&SRS=EPSG:4326&STYLES=

This does not (blank image): http://mrdata.usgs.gov/services/sc?REQUEST=GetMap&SERVICE=WMS&VERSION=1.3.0&WIDTH=256&HEIGHT=256&FORMAT=image/png&BBOX=-83.4,32,-78.4,35.3&LAYERS=South_Carolina_Lithology&CRS=EPSG:4326&STYLES=

Notice the 1.1.1 -> 1.3.0 and SRS->CRS are the only changes. Is this a problem with the service or is my second URL incorrect?

I've observed the same issue with other WMS services:

Works: http://mesonet.agron.iastate.edu/cgi-bin/mapserv/mapserv?map=/mesonet/www/apps/iemwebsite/data/wms/goes/conus_ir.map&SERVICE=WMS&REQUEST=GetMap&SERVICE=WMS&VERSION=1.1.1&WIDTH=256&HEIGHT=256&FORMAT=image/png&TRANSPARENT=TRUE&BBOX=-126,24,-66,50&LAYERS=conus_ir_4km_900913,conus_ir_4km&SRS=EPSG:4326&STYLES=

Does not work (blank image): http://mesonet.agron.iastate.edu/cgi-bin/mapserv/mapserv?map=/mesonet/www/apps/iemwebsite/data/wms/goes/conus_ir.map&SERVICE=WMS&REQUEST=GetMap&SERVICE=WMS&VERSION=1.3.0&WIDTH=256&HEIGHT=256&FORMAT=image/png&TRANSPARENT=TRUE&BBOX=-126,24,-66,50&LAYERS=conus_ir_4km_900913,conus_ir_4km&CRS=EPSG:4326&STYLES=

So I'm assuming it's an issue with my 1.3.0 URLs.

Answer 1

The difference between WMS 1.1.1 and 1.3.0 is two fold.

CHANGE NO 1 - CRS/SRS Usage

Use SRS for 1.1.1

Use CRS for 1.3.0

CHANGE No 2 - WMS 1.3.0 ONLY

The order of parameters for BBOX depends on whether the CRS definition has flipped axes. You will see this in the GetCapabilities request at 1.3.0 - the response should show the flipped axes.

BBOX=xmin,ymin,xmax,ymax NON-FLIPPED

BBOX=ymin,xmin,ymax,xmax FLIPPED

I have made a list of EPSG codes that need to be flipped by creating a SpatiaLite 4.3.0 database and then saving this SQL request to file:

SELECT auth_srid, has_flipped_axes, ref_sys_name, axis_1_name, axis_1_orientation, axis_2_name, axis_2_orientation FROM "spatial_ref_sys_all" WHERE auth_name = "epsg";

You will then see that EPSG:4326 needs to have flipped axes.

4326 1 WGS 84 Latitude North Longitude East

THIS IS THE CORRECTED 1.3.0 REQUEST

Change is BBOX=24,-126,50,-66

http://mesonet.agron.iastate.edu/cgi-bin/mapserv/mapserv?map=/mesonet/www/apps/iemwebsite/data/wms/goes/conus_ir.map&SERVICE=WMS&REQUEST=GetMap&VERSION=1.3.0&WIDTH=256&HEIGHT=256&FORMAT=image/png&TRANSPARENT=TRUE&BBOX=24,-126,50,-66&LAYERS=conus_ir_4km_900913,conus_ir_4km&CRS=EPSG:4326&STYLES&

Answer 2

Replace EPSG:4326 with CRS:84 and it works in both instances:

http://mrdata.usgs.gov/services/sc?REQUEST=GetMap&SERVICE=WMS&VERSION=1.3.0&WIDTH=256&HEIGHT=256&FORMAT=image/png&BBOX=-83.4,32,-78.4,35.3&LAYERS=South_Carolina_Lithology&CRS=CRS:84&STYLES&

http://mesonet.agron.iastate.edu/cgi-bin/mapserv/mapserv?map=/mesonet/www/apps/iemwebsite/data/wms/goes/conus_ir.map&SERVICE=WMS&REQUEST=GetMap&SERVICE=WMS&VERSION=1.3.0&WIDTH=256&HEIGHT=256&FORMAT=image/png&TRANSPARENT=TRUE&BBOX=-126,24,-66,50&LAYERS=conus_ir_4km_900913,conus_ir_4km&CRS=CRS:84&STYLES&

It's possibly worth noting this works because in WMS 1.1.1 EPSG:4326 is wrongly defined as having long/lat coordinate axes. In WMS 1.3.0 the correct axes lat/long are used.

CRS:84 is defined by OGC as having the same datum as EPSG:4326 (that is the World Geodetic System 1984 datum ~ EPSG::6326) but axis order of long/lat.

CRS:84 was introduced with the publication of the WMS 1.3.0 specification, to overcome this issue.