3D Picture Pick point Point of cloud

[Spin69]

Hello, 

I´m having a problem using a PickPoint in my 3D Picture. The thing is when I load STL, everything works (displayes point coordinates) but when a point cloud is loaded, nothing happens. Unfortunately I can´t give my code away so at least I will put here some screenshots.

front panel with point cloud loaded

PickPoint works for STL file

3D object creation

Thank you for your suggestions.

[wiebe@CARYA]

I'd say that a point is infinitely small, so you simply won't be able to click a point.

You probably have to do the hit detection yourself. And yes, that's probably hard.

You'll find out that you can't hit detect a line and a point, you'd probably have to find the point closest to the line, and test if the distance is acceptable.

Another option is to make a mesh from the points, but that's a huge topic on it's own.

[Spin69]

Thank you for your ideas.

I have tried to increase the point size by a large amout but it did not help either. So my guess is that LabVIEW does not count those points as the object (like surface of a STL object).

Unfortunately I don´t have neither time or skill to do the nearest point detection my self, since my deadline for this project is getting tighter every day 😀

Creating an invissible mesh from the cloud and picking a point from there is something I thinked about, but the output I need is the precise point I clicked on (for further cloud alignment by ICP algorythm).

[wiebe@CARYA]

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@Spin69 wrote:

Thank you for your ideas.

I have tried to increase the point size by a large amout but it did not help either. So my guess is that LabVIEW does not count those points as the object (like surface of a STL object).

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Not LabVIEW, but OpenGL\Mesa3D.

I doubt LabVIEW does much to do the hit detect.

The point size seems to be just rendering, and I would have put my money on that.

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@Spin69 wrote:

Creating an invissible mesh from the cloud and picking a point from there is something I thinked about, but the output I need is the precise point I clicked on (for further cloud alignment by ICP algorythm).

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The point (pun intended) is that you can't click exactly on a point.

The problem is also ambiguous. If you would do a manual hit detect, you get a conflict. It will return distances to all the points, and as you click through the object, are you looking for the point closest to the line, or closest to the camera? I don't think there's an easy answer.

Getting the distance from the line to the point doesn't seem too hard:

1) Get a 3D vector going through the camera and the click on the view plane

2) For all points, get the Distance from a point to a line - Wikipedia  (I'd use "Line defined by two points)

3) Use Array Min & Max to get the smallest distance and the index of the point.

I don't know by heart how to do 1), but it can't be that hard.