WMS layer - ArcMap doesnt recognize local CS?

Question

Hi there,

my map (ArcGIS desktop 10.5) has been assigned a local coordinate system (GCS_CH1903+). I add a WMS layer from a server which provides the data in the aforementioned  local coordinate system but ArcMap does not recognize it. A dialog pops up with a warning telling me that the transformation from WGS_1984 is required.

Why is that? Why doesnt recognize ArcMap that the data is available in a local coordinate system and therefore no transformation is required?

Many thanks, Rob

robert_at_work · Answer

Hi,

my data frame and the wms layer have the same coordinate system:

data frame -> coordinate system:

CH1903+_LV95
WKID: Authority: 2056 (EPSG)

WMS - Layer properties > Source > Data Source

Supported Coordinate Systems:
 EPSG:2056 - CH1903+_LV95
 EPSG:21781 - CH1903_LV03
 EPSG:4326 - GCS_WGS_1984

.....

All values above copied and pasted from ArcMap.

But when I add the WMS layer to the data frame I get a warning: "WMS datasource uses different coordinate system than data frame." - I dont want to transfrom from WGS84 to CH1903+_LV95 as the data is already provided in CH1903+_LV95

Rob

JayantaPoddar · Answer

I think the WMS layer is not in a local CS. WMS Servers support only a limited number of coordinate systems.

Please check this Setting the coordinate system of a WMS service—Help | ArcGIS Desktop

If the data frame is in a coordinate system that is not supported by the WMS server, ArcMap gets an image from the server in a supported coordinate system—in most cases, this will be in GCS 1984—and projects this image internally so it will display in your map.