Thread: [Visualpython-users] Contour lines using vPython

I'm looking for a way to draw E and B fields using vPython. I have the equations to find the vector at a point, but want to draw contour lines between two particles just as a start. Any suggestions or code segment that shows how to do that?

Thanks,
-d

The curve object will connect a list of points with line segments,
which sounds like what you want.

There is a trick to drawing field lines which you might wish to
implement, to avoid a systematic error. From a starting point where
you know the field direction, project a line in that direction and
evaluate the field at a new location on that line. Draw perpendiculars
to the two vectors and find where those perpendiculars meet (this is
assuming a 2D field). Imagine that point as the center of a circle,
and swing a circular arc around that center, starting from the first
point and ending on the line that is perpendicular to the second field
vector. Approximate the arc with a straight line. Evaluate the field
at the end of the arc, which will be nearly parallel to the second
field vector that you evaluated. Repeat.

At http://www.matterandinteractions.org/Content/Materials/programs2.html
you'll find a program fields.py which you might find interesting, as
it displays many properties of E and B fields, but not field lines
(nor equipotential lines/surfaces).

Bruce Sherwood

On Wed, Apr 20, 2011 at 6:47 AM,  <dal...@ea...> wrote:
> I'm looking for a way to draw E and B fields using vPython. I have the equations to find the vector at a point, but want to draw contour lines between two particles just as a start. Any suggestions or code segment that shows how to do that?
>
> Thanks,
> -d

If you want to find and draw the contours yourself, the curve object is an option. If you want to make a contour plot, I would suggest looking at matplotlib

http://matplotlib.sourceforge.net/


On Apr 20, 2011, at 12:09 PM, Bruce Sherwood wrote:

> The curve object will connect a list of points with line segments,
> which sounds like what you want.
> 
> There is a trick to drawing field lines which you might wish to
> implement, to avoid a systematic error. From a starting point where
> you know the field direction, project a line in that direction and
> evaluate the field at a new location on that line. Draw perpendiculars
> to the two vectors and find where those perpendiculars meet (this is
> assuming a 2D field). Imagine that point as the center of a circle,
> and swing a circular arc around that center, starting from the first
> point and ending on the line that is perpendicular to the second field
> vector. Approximate the arc with a straight line. Evaluate the field
> at the end of the arc, which will be nearly parallel to the second
> field vector that you evaluated. Repeat.
> 
> At http://www.matterandinteractions.org/Content/Materials/programs2.html
> you'll find a program fields.py which you might find interesting, as
> it displays many properties of E and B fields, but not field lines
> (nor equipotential lines/surfaces).
> 
> Bruce Sherwood
> 
> On Wed, Apr 20, 2011 at 6:47 AM,  <dal...@ea...> wrote:
>> I'm looking for a way to draw E and B fields using vPython. I have the equations to find the vector at a point, but want to draw contour lines between two particles just as a start. Any suggestions or code segment that shows how to do that?
>> 
>> Thanks,
>> -d
> 
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How about adding a shafttype property to the arrow so it could be 
boxed or round? Right now I'm just drawing a cone at the end of a rod 
and that looks fine so no big deal if it doesn't get added to the wish list.

-d

A reasonable suggestion. Presumably you've noticed that putting the
cylinder and the cone in a frame let's you move your rounded arrow as
a group just by changing the frame position.

Bruce Sherwood

On Sun, May 1, 2011 at 7:56 AM, Dan Aldrich <dal...@ea...> wrote:
> How about adding a shafttype property to the arrow so it could be
> boxed or round? Right now I'm just drawing a cone at the end of a rod
> and that looks fine so no big deal if it doesn't get added to the wish list.
>
> -d