Re: [Visualpython-users] Need coding suggestions

[Kadir H. <kha...@ya...>]

You can use the new EXTRUSION object to start with any arbitrary shaped polygon 
in 2D.
I do not know about the solid angles, but if it is able to reduce the number of 
"sides" of the
polygon down to 4 with some algorithm, then you will end up with a 4-sided 
polygon, or a
square if all with right angles.

Kadir





________________________________
From: Joe Heafner <hea...@gm...>
To: Visualpython-users <vis...@li...>
Sent: Wed, June 8, 2011 11:22:23 PM
Subject: [Visualpython-users] Need coding suggestions


I want to create some VPython simulations related to Gauss's law, flux, and 
solid angle. I want to get across the point that any arbitrarily shaped surface 
can, mathematically, be morphed into a sphere using the concept of solid angle. 
Is there a way to make an arbitrarily shaped patch of area morph SMOOTHLY into a 
square in VPython? Below is the code I have so far. It works, but it's not as 
smooth as I'd like it to be.


from visual import *   # a field arrow E = vector(1,-0.5,0) Earrow = 
arrow(pos=vector(0,0,0),axis=E,shaftwidth=0.01,color=color.red) Ehat = norm(E)  
# a patch of area # include option for circular patches direction = 
vector(1,1,1) patch = 
box(pos=(0,0,0),axis=direction,length=0.02,width=0.5,height=0.5) # patch 
morphing is smoother if height > width  # patch's initial area patch.height0 = 
patch.height patch.area = patch.height*patch.width print ("initial area        
", patch.area)  # a unit normal to patch nhat = norm(patch.axis) nhatarrow = 
arrow(pos=Earrow.pos,axis=nhat,shaftwidth=0.01,color=color.green)  scene.forward 
= -nhat  # get angle between the two vectors newtheta = acos(dot(Ehat,nhat)) # 
check for newtheta = 0 # check for newtheta = pi print ("angle               
",newtheta*180.0/pi) print ("predicted perp area ", patch.area * cos(newtheta))  
# get the new rotation axis newaxis = cross(Ehat,nhat)  # rotation animation 
scene.mouse.getclick() print ("rotating...")  dtheta=0.001 theta=0.0 while theta 
< newtheta:     rate(1000)     nhatarrow.rotate(angle=-dtheta,axis=newaxis)     
patch.rotate(angle=-dtheta,axis=newaxis)     patch.height = 
patch.height0*cos(abs(theta))     theta += dtheta patch.area = patch.area * 
cos(newtheta) patch.width = sqrt(patch.area) patch.height = patch.width  print 
("actual perp area    ", patch.height*patch.width) print ("patch axis 
",norm(patch.axis)) print ("field axis ",norm(Earrow.axis))


Joe HeafnerSent from my iPad