Re: MapProjectionDisplay question

Hi Stuart-

Stuart Maclean wrote:
I am trying to use the IDV classes to build navigated displays. I learnt the whole 'display side coordinate system' technique from in the visad/examples. In particular, how a call to MapProjection.setDefaultMapArea with a xy rectangle would result in the visad 'box' showing the xy area.

Do you do this before you set the projection?  Essentially, you
are changing the MapProjection when you change the default Map area.
By definition, CoordinateSystems are immutable, so a call to
change the default Map Area breaks that paradigm.  MapProjection
does not have a setDefaultMapArea for just that reason.

When moving to the higher level idv classes, I thought the corresponding call was in ucar.unidata.view.geoloc.MapProjectionDisplay.setMapArea ( ProjectionRect). This does not seem to do what I want. I did peek at the source code and noted that the comments for that method imply that the rectangle is in fact a lat/lon rectangle, not a cartesian one.

Can anyone shed any light on the setMapArea (and setMapRegion) methods, and how to use them correctly?

setMapArea and setMapRegion are used to zoom and pan the display,
not change the default area of coverage.  And as you noted,
setMapArea in particular only does this (incorrectly) by
assuming that the ProjectionRect is in lat/lon space.  In
reality, there should be a setMapArea that takes a LatLonRect
and the setMapArea(ProjectionRect) should just calculate
the LatLonRect from the projection in the display and then
call setMapRegion.

If you change the MapProjection by calling a setDefaultMapArea
method, then you need to call MapProjectionDisplay.setMapProjection
with the new MapProjection to make the box correspond to
the newly defined area.

Hope that helps.

Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307