Re: VisADLineArray() to make histogram bars - why do they float?

Hi Frank,

> I'm back with another question on using VisADLineArray to make histogram
> bars. In previous episodes (about a month back), with help from Bill, Tom
> and Ugo, I've created a vertical bar, attached it to a vertical ScaleMap,
> so that its length is determined by the variable on that axis. What I don't
> understand is how this length is determined: if I have a little line (in
> Jython)
> 
> # Idea from Ugo
> pBarMap = ScalarMap(intensity, DisplayShape)
> pBarScaleMap = ScalarMap(intensity, DisplayShapeScale)
> 
> pBars = VisADLineArray()
> pBars.vertexCount = 2
> x = 1.0
> pBars.coordinates = [ 0.0, 0.0, 0.0,    0.0, x, 0.0]
> pBarScaleMap.setRange(0.0, x/2.0) # Scale as recommended by Bill H.
> 
> I would expect that when this line is scaled, the first vertex should
> remain unchanged at [0.0, 0.0, 0.0]. Instead, there appears to be some
> vertical translation as well as scaling, so that the scaled lines no longer
> begin at the horizontal axis, but instead float at a height related to the
> intensity value to which they are mapped - they not only get bigger as the
> intensity increases, they also "float" higher.

Do you also have a ScalarMap of intensity to YAxis, or to
any other DisplayRealType? A map to YAxis could cause the
lines to rise with increasing intensity.

Cheers,
Bill