| Re: Displaying 3-D vector fields [message #32945 is a reply to message #32726] |
Tue, 19 November 2002 06:48   |
jim.blackwell
Messages: 11
Registered: November 2002
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Junior Member |
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"Rick Towler" <rtowler@u.washington.edu> wrote in message news:<arbgn1$1pbo$1@nntp6.u.washington.edu>...
> "Jim" <jim.blackwell@gsfc.nasa.gov> wrote
>> "Rick Towler" <rtowler@u.washington.edu> wrote
>>> "Jim" <jim.blackwell@gsfc.nasa.gov> wrote
>>>
>>>> what scales the size of the arrow (the length of the arrow relative to
>>>> the shaft)?
>>>
>>> The vector is scaled according to the sqrt() of the sum of the squares
> of
>>> the components of the magnitude. The *entire* vector is scaled, head
> and
>>> all since I am using the model's transformation matrix to do the work
> for
>>> me. The vector is not drawn if the magnitude is 0.
>>>
>>>
>>>> Is the default vector that is drawn of unit length ?
>>>
>>> Yes, the default vector is 1 unit long. It's default magnitude is
> [0,0,-1]
>>> which makes it parallel to the z axis pointing away from the viewer.
> It's
>>> default location is [0,0,0].
>>>
>>> -Rick
>>
>> I see. Say have you looked at the IDL program "vector_field" ? Seems
>> to do something similar in that it creates vectors, however I don't
>> know offhand how to implement this in IDL object graphics to see what
>> it looks like ?
>
> No. I haven't looked at it. I was satisfied with my vector as is. Well,
> sort of.
>
> After reading Mark's comments I was curious as to the impact of having large
> numbers of IDLgrModel objects in a scene. In our case it comes down to the
> cost of calculating the numerous transforms and internal procedural
> overhead.
>
> Ideally, as Mark has implemented in his barb plot, you'll have one model and
> one atom. Ignoring any parent models, IDL calculates a transform based on
> the one model and one atom transform (3x3 coord_conv transform) and applies
> it to all the vertices. Very efficient, but limiting.
>
> On the other end of the spectrum is a scene with 20k of my vector objects.
> Assuming we put our 20k models into a parent model, we need to do 40k matrix
> multiplies then apply each of those 20k transforms to the 4 verts that make
> up the vector. Not a model of efficiency but infinitely flexible.
>
> Somewhere in the middle is a single model which contains 20k IDLgrPolyline
> objects. I modified my original vector object and created a 3d vector field
> object following this design. I end up calculating the transform and
> applying it to the vertex data manually when the location or magnitude data
> is changed. What little I did play with it showed around a 30-40% increase
> in redraw speed with 20k vectors. Although unfinished, you are welcome to
> this code as well. The meat is there, you'll just need to add the dressing.
>
> In your case, none of these improvements will get you to the point where you
> will be able to interact in real time. It takes a long time to draw nearly
> 80K vertices. I think that you could go with any of them.
>
> But back to your question. You still seem to be looking for an answer.
> What do you need that Mark's barb plot or my vector can't provide?
>
> -Rick
Rick,
Mainly I just wanted to see what the differences were between the barb
plot and yours. My main problem is that 18K vectors is just too many
and I need some way to resample the grid so the grid is of lower
resolution.
Also, I wanted to be able to color the vectors based on their value.
Jim
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