Processing 1.0 - Processing Discourse - Align to velocity

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Index › Programming Questions & Help › OpenGL and 3D Libraries › Align to velocity - orientation

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Align to velocity - orientation (Read 3209 times)

koogy

Re: Align to velocity - orientation
Reply #15 - Feb 4^th, 2010, 4:16am

the rotate you mention isn't one of the standard rotate methods, is it, there are too many parameters.

rotate(-theAngle, crss.x, crss.y, crss.z);

can you post it here so people can see it.

and what are the 4 values it uses when it disappears? can you tell (i'm wondering whether you've got a (0, 0, 0) PVector somewhere which'll break the cross product. similarly the cross product of two identical or co-linear vectors is undefined.)

nardove

Re: Align to velocity - orientation
Reply #16 - Feb 4^th, 2010, 4:46am

The code I use is the one I post here in prev. replies.

I found the problem, theAngle variable gets equal to NaN This is because (like koogy said) two parallel vectors equals to a undefiend cross product.

I am using toxiclibs Vec3D http://toxiclibs.org/docs/core/

So now I know but the if function is not working
Code:

float theAngle = new_dir.angleBetween(new_up); 
if (theAngle == Float.NaN) println("ERROR");

How can I compare the NaN that toxic's angleBetween returns?

Cheers
rS

koogy God Member Offline Posts: 788	Re: Align to velocity - orientation Reply #17 - Feb 4^th, 2010, 5:04am i'd try Float theAngle = new_dir... then do the check for Nan. might need to use equals() rather than == as it's a class then use -theAngle.floatValue() in the rotate() to get a float from a Float. > two parallel vectors equals to a undefiend cross product. hey, lucky guess! or years of experience. you decide 8)

nardove Full Member Offline Posts: 189 UK	Re: Align to velocity - orientation Reply #18 - Feb 4^th, 2010, 5:17am I will say both, experience and lucky, if you get the result either way it always adds to the experience. I am struggling to make the comparison. equals() only works for Strings, and I cant cast theAngle as string because I get an error. I am so close I can almost taste it. Cheers rS

koogy

Re: Align to velocity - orientation
Reply #19 - Feb 4^th, 2010, 5:24am

> equals() only works for Strings

no, every Class has an equals() method which lets you compare the value contained by the object rather than the objects themselves. (um, easier to explain if you know C... pointers vs contents)

let the professionals do it:
http://www.ensta.fr/~diam/java/online/notes-java/data/expressions/22compareobjects.html

koogy God Member Offline Posts: 788	Re: Align to velocity - orientation Reply #20 - Feb 4^th, 2010, 5:27am actually, this is a better link http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Float.html and there's an isNaN() menthod on Float which you should use instead of equals. you can even leave theAngle as a float (small f) and use if (Float.isNaN(theAngle)) { ... }

nardove Full Member Offline Posts: 189 UK	Re: Align to velocity - orientation Reply #21 - Feb 4^th, 2010, 5:31am koogy, that works now when theAngle is NaN should I make it = 0.0 ? or what is the usual fix when that happens Much appreciated all your help rS

nardove

Re: Align to velocity - orientation
Reply #22 - Feb 4^th, 2010, 6:54am

toxi said:

"If you're getting a NaN result (= Not a Number) then
your input vectors aren't normalized and you should use this version
of the function:

myVec.angleBetween(otherVec, true);

That will internally use normalized copies of both vectors to do the
calculation (but won't normalize your original vectors)."

And so far no NaNs

Cheers
rS

toxi Full Member Offline Posts: 203	Re: Align to velocity - orientation Reply #23 - Feb 9^th, 2010, 4:56am Glad it helped! Just for the record, the javadocs for this method do mention the normalization aspect: "Computes the angle between this vector and vector V. This function assumes both vectors are normalized, if this can't be guaranteed, use the alternative implementation angleBetween(Vec3D, boolean)"
	postspectacular.com \| toxi.co.uk

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