[Geomoose-users] using Google layers as background

[Brent Fraser]

John,

1)  Technically they describe the same coordinate system, but 3785 is 
deprecated and replaced by 3875 as the "official" EPSG code.  900913 was 
the original, "user defined" (aka non-offical) code so has been in use 
longer (and some systems may not have adopted the official code yet).  
So go with 3875 if possible, but you could use 900913 if necessary.

2)  You should demand(!) that the WMS servers serve up the data in your 
display coordinate system (it off-loads the re-projection to the 
servers)., but if they don't advertise that they support it, you could 
get GeoMOOSE to warp it on the fly by including a projection='EPSG:4326' 
option in the <map-source> tag.  Be warned that is only does a warp and 
the layers will not line up as you zoom out.  The solution is to set up 
mapserver to act as a WMS client, do the reprojection and serve the 
result in your coordinates system of choice (e.g. 3875).

3).  Correct.  And add a PROJECTION block to the LAYER so mapserver 
knows which coordinate system they are in.

Best Regards,
Brent Fraser


On 4/15/2011 1:25 PM, John Callahan wrote:
> I'm creating a GeoMoose application that will use the various Google 
> tile layers as backgrounds.  (I originally created a basic app in my 
> local state plane projection but then realized that the Google-like 
> backgrounds are critical.)   I've downloaded the Web Mercator demo and 
> am looking at http://geomoose.org/howto/commercial_layers.html for 
> guidance.  As I go through this, a few quick questions:
>
> 1) Should I use EPSG:3857, EPSG:3785 or EPSG:900913?  Or does it 
> matter as long as Proj4 supports it and there's a corresponding file 
> in proj4js\lib\defs
>
> 2) In the mapbook file, should all the data sources (nearly all of WMS 
> type) have the same projection attribute, such as projection="EPSG:3857"?
>
> 3) Just to confirm, my raw data files do not need to be in the "web 
> mercator" projection, only the MAP Projection and Extent parameters in 
> the map files, correct?
>
>
> - John
>
> ***********************************
> John Callahan, Research Scientist
> Delaware Geological Survey
> University of Delaware
> URL: http://www.dgs.udel.edu
> *******************************
>
>
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