[Visualpython-users] IEEE NaN handling, rotating scene with mouse

[John K. <joh...@ho...>]

A suggestion for future versions of Vpython:

It would be very useful to enable the curve feature to "pick up the pen" 
(leave a break in plotting) when it encounters the IEEE NaN (non-a-number) 
as a position coordinate.  This would allow the user to generate a 
discontinuous curve with a single curve object by introducing NaN's into the 
position coordinates.  (Is there perhaps another way to get this same 
behavior in the mean time?)  Right now, NaN's crash the curve routine.  (Now 
I'm wondering how it handles IEEE Inf.)

Also, I've been noticing that rotating the scene with the mouse works in an 
intuitive way until the view is along the y-axis.  The intuitive way is for 
up-down mouse movement to rotate along the vertical line of the window and 
for left-right mousemovent to rotate along the horizontal line.  The way it 
actually works is for horizontal movement to rotate in plane perpendicular 
to the y-axis (what would be azimuthal angle in spherical coordinates, 
except in x-z plane), and vertical movement to rotate to and from the y-axis 
(what would be polar angle in spherical coords, except from y-axis, not z).  
Is there any simple way to change this bevavior? At least to change the 
preferred axis?

BTW a good example of the intuitive rotational behavior is at the 
outstanding java applet at Nasa's Marshall Center: 
http://liftoff.msfc.nasa.gov/realtime/jtrack/3d/JTrack3d.html
Worth examining in its own right!

JK

P.S. This is the only way I could find to generate NaN without crashing:
nan = struct.unpack("f", '\xff\xff\xff\xff').  Anyone know of a more 
straight-forward way?  JK


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