Longitude in VisAD

Hi Bill,

I have been playing with EarthMaps and have met some
behaviour of longitude which I am having trouble predicting.

I have Scalar Maps
    RealType.Longitude -> Display.XAxis: range -180.0, 180.0
    RealType.Latitude ->  Display.YAxis: range -90.0, 90.0

This means the right edge of the map is at 180 degrees.

I find that a line of constant latitude from -180->150 gives a line
from -180->150. If I try -180->160 I get the "short" distance from
160->180.

Trying 10->180 on its own behaves as expected but if I include
a 0->360 as well, the 10->180 line is drawn as -180->10 and nothing
is drawn for the 0->360 line (I expect it is trying to draw 0->0.
Both lines are represented as Gridded2DDoubleSet as part of a UnionSet.

Could you give me a pointer to how RealType.Longitude is meant 
to behave. Indeed is it meant for spherical polar coordinates
or for geographic mapping of earth data?

Thanks

Geoff
-- 
Bureau of Meteorology
Phone (03) 9669 4827