Hi, sorry for the newbie question but I've been looking for how to do this for quite a while now!

In the HDK, how do I find the number of the closest point in my gdp to a world position? For example, I want to find the number of the point in my geometry that is closest to position (1,2,3).

I have seen the classes like UT_PointTree, but I can't for the life of me get them initialized properly. Anyone have an example?

Something like this should work:

#include <GEO/GEO_PointTree.h>

GA_Offset
getNearestPoint(const GU_Detail *gdp, const UT_Vector3D &pos, fpreal maxdist)
{
GEO_PointTreeGAOffset tree;

tree.build(gdp);

// Get the offset of the nearest point, within maxdist.
return tree.findNearestIdx(pos, maxdist);
}

Excellent, thanks Graham!

Just as a warning, if you'll be doing a lot of closest point queries, you'll definitely want to save the GA_PointTreeGAOffset, instead of recomputing it every time, and in that case, I seem to recall that you can save even more time by reusing the same results queue and passing it into the closest point query. I don't remember the class name, but it'd be in UT_KDTree.h; GEO_PointTreeGAOffset is a subclass of UT_KDTree. It's something along the lines of ut_KDQueue, I think.

Oh, and feel free to ask any questions. It's especially important for “newbies” to ask, since it can be pretty difficult to get started with the HDK, and it'd be unfortunate if there wasn't adequate help. :wink:

Yea thanks for the tips, definitely making sure to only build the tree once

Works well!

Do you know if there's similar functionality for faces? I'd like to find the closest face and its normal to a given point.

KMcNamara
Do you know if there's similar functionality for faces? I'd like to find the closest face and its normal to a given point.

I think UT_RTree does something like that, though I've never used it. I think it's queried (maybe even lazily constructed?) by calling UTgetIntersectingItems, though I don't know if it'd just say yes/no whether something intersects. GU_RayIntersect can find things like the minimum distance from primitives to a ray, so it might have something like that too, but I'm not sure.

Ah, found a good answer here: http://forums.odforce.net/topic/12691-closest-point-on-the-primitive/?p=79743 [forums.odforce.net]

Thanks!

So now I'm trying to use proximityPoint to get a collection of primitives around the point. However, I'm getting a segfault with this - ideas? Not sure if I'm doing the right thing with the GU_ProximityHelper?


GU_RayIntersect rint(gdp);
UT_Array<GU_MinInfo> hitList;
const GU_ProximityHelper* proxyHelp;
rint.proximityPoint(hitList, UT_Vector3(0.0,1.0,0.0), true, proxyHelp, 1.0);

for (auto i = hitList.begin(); i != hitList.end(); ++i)
{
i.item().prim()->computeNormal(); // Just see if we can access the prim
}