Compute distance btwn 2 Objects?

[positron]

In an expression, I want to dynamically compute the distance between two objects, & conditionalize it so that if the distance is less than the radius of object 'a' then object 'b' visibility is turned on or off.
Kind of a ghetto object collision....
Can someone help me with the distance compute algorithm? From centerpoint to centerpoint is fine..

Help? Thank you.

[campbell]

vector maths:

pnt1 - pnt2 : vector between the pnts
sqrt(vec.x^2 + vec.y^2 + vec.z^2)

[joojaa]

Yes and the pythagoran thing is so much used that theres actualy a command to do it its called mag(vector), its slightly more economic (to type and execute id imagine) but its that fiunction allright.

So mag(pnt1 -pnt2). Would do the same thing.

But every one with any deecent education should know this? no?

[markwilkins]

The easiest way to find the world space distance between two objects is to make a distanceBetween node.

First, make a distanceBetween node.

Then, feed the (object 1).worldSpace[0] matrix into the first matrix input. Feed the object 2 worldSpace[0] attributes into the second matrix input. Open the node in the attribute editor and set the "point" attributes to zero. (The reason this works like this is that the worldSpace matrix contains all the information necessary to transform a point in local space to world space. You want to compare the positions of the centers of your two objects, which are at 0, 0, 0 in local space.)

Finally, make an expression that turns off the visibility of one or the other when the distanceBetween's distance attribute is lower than a certain threshold.

I just tested the above, and it works.

The other way to do this, using the xform command to get the positions, converting to a vector, and using "mag," is a bad idea because using MEL commands like xform in an expression will slow down your scene evaluation considerably. Better to use the distanceBetween utility node.

-- Mark

[joojaa]

mag is an expression! Not mel so it works fine in expressions. Also using anode is fine for 2 points but if its a prticle thng then a node is not so cool

[markwilkins]

mag is an expression!

Yeah, but to find a world-space distance between two objects you need to get their world space positions with Xform (a nasty MEL command,) or else get their world space matrices and umm do some math.

And yes, a particle expression would be just fine for this if you're doing it with particles... of course you run into the same problem if you are trying to find distances between two different particle objects!!

-- Mark

[joojaa]

Well it works fine as liong as you havent moved the shape (Wich you dont need that often!), Also reclculating from mattrices isnt that bad... (altough supid it doesent exsist as an expression...)