Triton - update to sea level policy

[gwaldron]

If you are a Triton user, please note this recent change that might affect you.

By default Triton would render at a sea level of 0 meters above the ellipsoid. We decided it made more sense to render the Triton ocean at "MSL=0", that is, at the Mean Sea Level of zero meters according to the well-known EGM96 geoid.

You can set a different geoid to use in the API, for example:

tritonLayer->setVerticalDatum("egm2008"); // render Triton on the EGM2008 geoid
tritonLayer->setVerticalDatum(""); // render Triton on the ellipsoid (old default)

Or in the earth file:

<Triton>
   <vdatum>egm96</vdatum>
   ...

Supported geoids include egm96 (the default), egm84, and egm2008. Or you can specify none or ellipsoid to render Triton using the old ellipsoidal method.

Hope this makes sense. Let us know if you have any questions!