| Re: Image Overlays on Google Earth with KML Files [message #81856] |
Thu, 01 November 2012 11:19  |
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DavidF[1]
Messages: 94
Registered: April 2012
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Nata writes:
> I am glad that my question has inspired you...
>
> I found a very good library to create KML files in IDL. I didn't start using it but it seems very complete to me. Take a look :
>
> http://code.google.com/p/kdm-idl/
Yes, I used many of the ideas in this library for my own code.
It had a few too many dependencies for me, and too little
documentation. But, it looks very complete. And I can certainly
appreciate what a lot of work went into it.
> One question I have is about the projection... In your code your are projecting everything to an Equirectangular projection. Is this the Google Earth exact "projection"?
I don't know what you mean by "exact" projection. But, yes, this is
the projection Google Earth uses. The cgImage2KML program converts
from whatever projection your image is using to this projection before
it creates the PNG file that is placed on Google Earth.
> I am asking this because I have found some differences between the IDL Mercator projection and the projection used by Google Maps (that is also Mercator). I don't exactly know the reason but if I want precision of meters I have to use my own code to project things.
If you are talking about the Mercator projection that is set up
with MAP_SET, then you are certainly correct. This map projection
is wrong. I have experienced no such problem with the Mercator
projection set up with Map_Proj_Init, and these GCTP projections
are the only ones used by cgMap, my map coordinate object, which
is what I use for ALL of my map projection work.
Cheers,
David
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