| "Object Graphics and Vectors" Reloaded [message #40319] |
Tue, 03 August 2004 05:31  |
Ralf Schaa
Messages: 37
Registered: June 2001
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Member |
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G'day group,
a few days ago I had a question of how to plot a spacecraft trajectory
with object graphics. After David's hint to use IDLgrPolyline when
plotting an orbit around a sphere in 3d I was able to do that, and it
looks great.
But now I am stucked with this:
How to plot some vectors (the spacecraft's velocity vector) for some
defined times on the spacecraft trajectory.
I found Rick Towlers 'vector' Object , which he posted 2002 and it
plotted a vector, unfortunately not in the right scale, i tried the
coord_conv but this did not help ...
Of course there is a scaling problem, since the magnitude of the s/c
velocity is much less than the scale of the coordinate system, so i
multplied with a factor that makes sure I'd see the vector ...
So, has someone a clue of how to set the scales right from the
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| Re: "Object Graphics and Vectors" Reloaded [message #40423 is a reply to message #40319] |
Thu, 05 August 2004 02:57  |
Ralf Schaa
Messages: 37
Registered: June 2001
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Member |
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David Fanning wrote:
> [...]
> I don't know. You are confusing me. :-)
Yes. I'm confusing myself ... but I was able to manage the problem. I
now do it with the polygon object itself. I was not able to get that
vector object in the place the way I wanted, but the polygons did,
heureka , now I know what these verteces are ... :-)
Thanks for your responses, David.
Cheers
-Ralf
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| Re: "Object Graphics and Vectors" Reloaded [message #40438 is a reply to message #40319] |
Wed, 04 August 2004 11:06 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Ralf Schaa writes:
> okay, I thought 'well, before taking David's hint I give it a try
> myself, this can't be soo hard ...'
>
> This is what I have:
> a nice 3d object plot in data-coordinates with all rangings from -2.5e4
> to 2.5e4, so far so good.
> Now I add a vector with Rick Towler's vector object, which needs as
> input a 'location' (the startpoint of the vector) and a 'magnitude' (the
> endpoint), these are defined in normalized coordinates.
> Okay, all i have to do is give the location and the magnitude in values
> which are near my ranging-values, actually I calculated them with the
> formula taking from the idl help:
>
> NormX = -range[0]/(range[1]-range[0]) + 1/(range[1]-range[0]) * DataX
>
> I need the other way round:
>
> DataX = NormX * ((range[1]-range[0])) + range[0]
>
> e.g a vector in normalized coordinates from [0,0,0] to [1,1,1]
> would be in datacoordinates
> from [range[0],range[0],range[0]]
> to [3*range[1],3*range[1],3*range[1]]
>
> but nothing exciting happened ...
>
> so where is my bug ?
I don't know. You are confusing me. :-)
Here is what I would do. First, figure out
how big a "unit" vector is in your coordinate
system. Perhaps it is 0.05 of the length of the
universe:
unitLen = 2.5e4 * 2 * 0.05
Then find out the current "range" of the vector
object:
vector -> GetProperty, XRange=xr, YRange=yr, ZRange=zr
Suppose the vector you wish to draw is 3.2 times the
size of a unit vector.
xs = Normalize(xr, Position=[0, 3.2*unitLen])
ys = Normalize(yr, Position=[0, 3.2*unitLen])
zs = Normalize(zr, Position=[0, 3.2*unitLen])
Now, scale the vector:
vector -> SetProperty, XCoord_Conv=xs, $
YCoord_Conv=ys, ZCoord_Conv=zs
Without something to *see*, I don't have a great deal
of confidence in this solution. But I think it has to
be *something* like that. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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