[idvusers] help with Blue Marble Images and IDV codebase

I am trying to incorporate Blue Marble Next Gen images into an IDV based app.

The images have Plat Carre map projection, a very simple lat -> y, lon -> x.

I load the image, using e.g. GIFAdapter and then use DataUtility to get a 
FlatField, call it f1, whose mathtype is

((ImageElement, ImageLine) -> (Red, Green, Blue))

(I actually snip/crop the orig image using BufferedImage.getSubimage but i 
think that is working ok)

I then build a new FlatField f2 with domain SpatialEarth2DTuple and same range as f1. I am calling f2.setSamples(f1.getFloats(false)) to transfer the range values. (I suspect that I should be using a CoordinateSystem somewhere here to transform ElementLine -> Lon etc ??)

If I then take f2 and build a visad style of DisplayImpl, with 5 scalar maps (lat,lon,r,g,b) and a single DataReferenceImpl, then the image shows up as expected in the displayImpl.

But I have got used to using IDV's DisplayMaster and subclasses of Displayable. For instance, I load bathy data into a Contour2DDisplayable and that works great. I get all the map projection stuff for free with the IDV classes.

My actual problem is that I think I am supposed to be using Grid2DDisplayable to incorporate my flatfield f2 into an IDV DisplayMaster. Alas it is not working. I see no image data. Is this the wrong class? It subclasses RGBDisplayable so I thought I was on the right track.

Any help gratefully appreciated.

Stuart Maclean