[mapserver-users] EPSG:4326 with WMS 1.3.0
Olivier Terral
olivier.terral at geomatys.com
Fri Nov 19 08:51:16 PST 2010
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
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