Coordinate System Overrides

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Coordinate System Overrides

nate_tate
Hello fellow GIS,  I'm new at using MG opensource and Maestro, so still trying to get use to it. I would like to ask for some help or pointers.  I have an Oracle db setup and Maestro is connected to it and reads/see the spatial tables. In the oracle db, the source SRID that is set up on the spatial tables is 4326 and 8307, which is equivalent to each other.(see screenshot).


I use the edit tool to override the source 4326 and 8307 SRID into 3857(see screenshot2).


I am planning to use Openstreet map and or Google map as the base map and overlay the spatial tables in Oracle on top of it. Hence the overrides to use SRID 3857 which is the same as 900913 that OSM and Google map uses.  I guess my concern  is that will this method work as far as the vector layer from Oracle will fall/overlay on top of the base map correctly?  Is this a reasonable sound approach?  

Thanks,
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Re: Coordinate System Overrides

Jackie Ng
Coordinate System Overrides is a slight misnomer.

What you're actually overriding is the declaration of what the coordinates in OracleSrid4326 and OracleSrid8307 represent. You are not transforming anything by changing the coordinate system here.

Coordinate System Overrides is you telling MapGuide: If you see data from this Feature Source in OracleSrid4326, I want you to treat any data as though it were in the coordinate system of <your selected coord sys WKT>

So to then answer your actual question. The coordinate system declared in your Map Definition is the actual source of truth. Any layer -> feature source whose coordinate system does not match the one in the map def is automatically reprojected by MapGuide.

So what you really want (for your data to line up with OSM), is to have a Map Definition in WGS84.PseudoMercator (EPSG:3857). MapGuide will reproject any data from layers/featuresources in that map def that don't have the same CS as the one you declared on the map def.

- Jackie
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Re: Coordinate System Overrides

nate_tate
Thank you Jackie.  
What about if the Oracle SRID is already in 3857.  If I transform the SRID4326 into SRID3857 at the data base level, then it should fall/overlay correctly?
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Re: Coordinate System Overrides

Jackie Ng
Yes, if the data is natively 3857 it should line up correctly.

- Jackie