[Proj] Re: Can I set the unit of Mercator Porjection? I'm trying to overlay shp file to google map.

Frank Warmerdam warmerdam at pobox.com
Thu Nov 2 10:10:24 EST 2006

baijianhua wrote:
> Thanks for response. I think you are right that it doesn't make sense to use 
> degrees as a linear unit for a projected coordinate system in PROJ, but I'm 
> wondering why google map can use Decimal Degree as the coordinate for markers, 
> do you think they are doing some kind of internal coordinate system 
> transformation?


Yes, I think this is what they are doing.

 > And, I think it's also very common that we render 2 dimension
> map using decimal degree as unit. So I'm a little confusing what we are 
> actually doing when we talking about decimal degree in 2 dimension map. Forgive 
> me that maybe I'm asking stupid questions, I'm not very famirliar in this field.

Any time you know the projected coordinate and the coordinate system you can
turn the location back into decimal degrees.  This is often done for display
purposes since projected coordinates are often confusing to the layman.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org

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