Why raycaster works with an array of objects and it doesn't work with scene.children?

Questions
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#1

I set raycaster ray from an object in the scene (not the usual mouse+camera) using:

depthRig.getWorldPosition(raystart);  
depthRig.getWorldDirection(raydir);
raydir.multiplyScalar(-1);
raycaster.set(raystart, raydir);

Then, when I pass the objects via an array, I get stable performance:

intersects = raycaster.intersectObjects( models, true );

But when I pass them via the scene:

intersects = raycaster.intersectObjects( scene.children, true );

I get a sweeping distance, that causes this effect:
raycaster_issue2

Of course, I could always use an array of objects to prevent this, but:
a) it might not be always convenient,
b) I wonder, is this a three.js raycaster issue, or there is a cure?

#2

I’m not sure what your issue is and what you mean by the sweeping distance.

I’m guessing that raycasting performance is slow, if that’s the case - I suggest you search the forum for words “slow” and “raycast” it’s a surprisingly popular topic with a lot of answers, including some from myself.

Spoiler: use a spatial index.

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#3

I’m not sure what your issue is and what you mean by the sweeping distance.

I thought the animated capture would clearly depict the problem…

By “sweeping distance” I mean the returned distance by raycaster that sweeps in a sawtooth waveform style, between the intersection point (max distance) of the ray with the mesh, and the ray’s origin (minimum distance), which causes the ray to vary in length, as is shown clearly on the animated gif above.

You can also see in the console on the right part of the gif, the distance itself returned with the line console.log(intersects[0].distance)

So, this post is not about ‘slow performance’, I have searched the forum, but 99.9% of the issues either refer to the classic mouse-camera case -which is not my case, or are irrelevant.

My question is very different:
Why raycaster works with an array of objects and it doesn’t work with scene.children?
I updated the title to this question.
Thanks.

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#4

Nevermind, on a second thought, scanning the whole scene would be highly inefficient, so I’ll keep using arrays and a spatial + model partitioning system to minimize processing time too.

That said, I think there is a three.js bug in such approaches, hiding somewhere… :ant:

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#5

I’m sure I’m not a normal person, what it looked to me was a cut-out of a 2d picture of a woman, with a red line and a dot moving across the screen. On the right I saw a console with a bunch of numbers scrolling. And mysterious “max-ms” and “min-ms” numbers changing value. Apparently the console values were printed from line 251 of a file called “script.js”. To me that’s too little info to answer following questions:

  • is the woman a 3d model being rendered in three.js?
  • if answer to above is “yes”, is the dot representing a 3d point?
  • is line representing direction of the ray? And if so, why does it suddenly cut off at some point?
  • if the red dot and a line represent a ray, does it actually intersect the model? Because on the image it seems to be overlaid above the model, so it seems like it never actually hits the model.
  • what are the numbers scrolling in the console?

I still don’t get it. You mean distance from ray origin to first(nearest) contact(hit)? Also I’m not sure I understand the sawtooth reference, in signal processing world it usually refers to a triangular wave pattern, but I’m not sure if that’s the application here and if it is - I don’t understand what is X and what is Y on that graph, like for example X=displacement of ray origin along the ray direction and Y=distance from ray origin to nearest contact. I.e. I don’t understand the function that is being plotted.

Anyway, I’m glad that you seem to have found your answer. If you still think there’s a bug somewhere, maybe put together an jsfiddle or something similar to demo the issue. I know there are smarter people than me here, so even if I can’t help, I’m sure others might, given more information.

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#6

LOL, we’ve turned a trivial thing to rocket-science! :grinning_face_with_smiling_eyes:

what it looked to me was a cut-out of a 2d picture of a woman, with a red line and a dot moving across the screen

That would be …offensive to the nature of three.js, we’re coding three.js here, not HTML! :grinning_face_with_smiling_eyes:
(look at ‘ENTER VR’ at the bottom).

You mean distance from ray origin to first(nearest) contact(hit)?

Yes.

Also I’m not sure I understand the sawtooth reference, in signal processing world it usually refers to a triangular wave pattern, but I’m not sure if that’s the application here and if it is - I don’t understand what is X and what is Y on that graph, like for example X=displacement of ray origin along the ray direction and Y=distance from ray origin to nearest contact. I.e. I don’t understand the function that is being plotted.

sawtooth waveform:

sawtooth

X is time, and Y is the distance returned by raycaster that is measured between the ray’s origin and the ray’s nearest intersection point.
The issue here, is that instead of being stable with a stable ray and object, it “sweeps” between zero (origin) and the nearest intersection according to the above waveform.
I borrowed the term from sweep generators that use a sawtooth waveform to sweep a frequency, to measure the frequency reponse of a circuit, a loudspeaker, or a room.

Anyway, I’m glad that you seem to have found your answer.

Thanks!

If you still think there’s a bug somewhere, maybe put together an jsfiddle or something similar to demo the issue. I know there are smarter people than me here, so even if I can’t help, I’m sure others might, given more information.

Well, I don’t see much interest anyway… and in several posts I’ve read, I saw that they’re using arrays too.

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