[mapserver-users] EPSG:4326 with WMS 1.3.0

[Rahkonen Jukka]

Hi,

WMS 1.3.0 standard does not say that maps must not be North-up any more. You may see rotated maps if you open gml vector data returned by WFS 1.1.0 service with a client than can't handle axis flipping but that is a client error, the map should be North up also in that case. By looking at the map image you cannot say which axis is x and which y because 'x' and 'y' are just axis names and it is another story which one means East-West and which one North-South. Look at your BBOX=-90,-180,90,180 and the image and you'll see that the second pair -180,180 is drawn in East-West axis.

-Jukka Rahkonen-




-----Alkuperäinen viesti-----
Lähettäjä: mapserver-users-bounces at lists.osgeo.org puolesta: Olivier Terral
Lähetetty: pe 19.11.2010 18:51
Vastaanottaja: mapserver-users at lists.osgeo.org
Aihe: [mapserver-users] EPSG:4326 with WMS 1.3.0
 
Hello,

I've a doubt about how MapServer handles the EPSG:4326 CRS in WMS 1.3.0.

With the CRS EPSG:4326, longitude/latitude are reverted so the map 
should be rotated by 90° on the right, with latitude on X axis and 
longitude on y axis . But on the example below  the map has longitude on 
X axis and latitude on Y axis :

http://demo.mapserver.org/cgi-bin/wms?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=-90,-180,90,180&CRS=EPSG:4326&WIDTH=953&HEIGHT=480&LAYERS=bluemarble,cities&STYLES=,&FORMAT=image/png&DPI=96&TRANSPARENT=true 


See extract of the WMS 1.3.0 spec below:

################################################################################ 


6.7.3.1 Introduction
....

The Layer CRS has two axes, denoted x and y. The x axis is the first 
axis in the CRS definition, the y axis is
the second axis. Depending on the particular CRS, the x axis may or may 
not be oriented West-to-East, and
the y axis may or may not be oriented South-to-North. The WMS portrayal 
operation shall account for axis
order, origin and direction in the Layer CRS when projecting geographic 
information from a Layer CRS to the
Map CS.
Coordinates shall be listed in the order defined by the CRS and shall be 
mapped appropriately to the Map CS
i and j axes, swapping axis order as needed during the projection 
operation. Many projected coordinate
reference systems have an axis and coordinate order other than easting, 
northing. For example, the Uniform
Coordinate System used in Finland (EPSG:2393) orders northing before 
easting. EPSG geographic
coordinate reference systems follow ISO 6709 and always list latitude 
before longitude.

....
EXAMPLE:
EPSG:4326 refers to WGS 84 geographic latitude, then longitude. That is, 
in this CRS the X axis
corresponds to latitude, and the Y axis to longitude.

################################################################################ 




So, what is the right image to obtain, rotated or not?



Thanks in advance.

Bye

             Olivier Terral
_______________________________________________
mapserver-users mailing list
mapserver-users at lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/mapserver-users