newbie question

Greetings

I'd really appreciate some help with my lack of understanding of the
visad model. I'm trying to display the postions (lat, long, alt) of some
weather stations as a learning exercise.

I'm getting the error
"RealType Longitude occurs more than once: ShadowType.testIndices"
when the Java 3D viewer comes up, and nothing else.

I assume that my logic is at fault (it was a strain just getting it to
compile).

{If I get this to work I next want to show the period of operation
(span) of the stations as a bar in the Z axis, rather than station
altitude.}

Here is the relevant bit of code I think:
__________________________________________________
RealTupleType stationSpan = new RealTupleType(RealType.Latitude,
RealType.Longitude, RealType.Altitude);

int nstations=testquery.stations.size(); // the number of stations to
display

float span[][]=new float[3][nstations];

for (int i=0;i<nstations;i++){
        WeatherStation current=(WeatherStation)
testquery.stations.elementAt(i); 

        span[0][i]=(float) current.latitude;
        span[1][i]=(float) current.longitude;
        span[2][i]=(float) current.altitude;

}

final DataReference stations_ref = new DataReferenceImpl("stations");

stations_ref.setData(new Gridded3DSet(stationSpan,span,nstations));

DisplayImpl display = new DisplayImplJ3D("image display");

// map earth coordinates to display coordinates

display.addMap(new ScalarMap(RealType.Latitude, Display.XAxis));
display.addMap(new ScalarMap(RealType.Longitude, Display.YAxis));
display.addMap(new ScalarMap(RealType.Altitude, Display.ZAxis));

display.addReference(stations_ref);
______________________________________________
Thanks for any advice
-- 
Matthew Laurenson
National Agriculture Research Center
Ministry of Agriculture, Forestry and Fisheries
3-1-1 Kannondai
Tsukuba
Ibaraki 305-8666
JAPAN

ph       +81-298-38-7025
fax      +81-298-38-8551