# Is a single point "geometry"?

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This is purely a semantic question and I mean in terms of 3D graphics, not math. (though perhaps there's no such distinction)

Or is this like asking if viruses are alive?  (but please let's not have THAT discussion, hehe )

My thought is, as a point technically is a (graphics-) primitive, it is geometry, right? But as I might be completely wrong, I thought I'd come here and start a lively discussion about it.

Edited by Farmfield

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Geometry means earth-measure/meter, as you can't measure anything with a point, as it has no distance, then it might not be able to be classed as geometry.

It does hold a memory footprint, so in computer graphics, it has that being similar to geometry.

Perhaps a point could be classed as degenerate geometry, i.e. from wiki:

• A point is a degenerate circle, namely one with radius 0.

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The question would be answered by the answer to if a a graphics primitive must be a geometric primitive? Because if it is, a point would be geometry. But I suspect that leads us into the "is a Virus alive" thing.

* Edit: Suddenly I'm starting to think that object primitives (like a primitive sphere) probably isn't geometry either, they are geometry representations, so that would make a point non-geometry. *

The circle thing is weird, though, a circle is a curve - but then again, a curve with an infinitesimal length, would be a point (I guess).

Now, this is of course not very important, but I was phrasing a description of a point and the question popped up in my mind - and it's kind of an interesting question, though it's lack of much relevance.

Edited by Farmfield

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I just think of a point as a location in space which you can position other geometry at (an instance, a dot, sprite, etc). If you don't place any other geometry there, it can't be rendered. So on its own, it's nothing but a placeholder.

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Hehe, that's not true in Houdini, though, as points render as primitive spheres as default - but I agree. I define a point as a location, so that's not something. I'm not sure, though, that my definition is correct in terms of terminology - which is what this is all about, or rather, my first post is.

My current hypothesis is a point is a primitive and that primitives are not geometry but geometry representations.

Edited by Farmfield

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2 minutes ago, Farmfield said:

Hehe, that's not true in Houdini, though, as points render as primitive spheres as default - but I agree. I define a point as a location, so that's not something. I'm not sure, though, that my definition is correct in terms of terminology - which is what this is all about, or rather, my first post is.

Well as you say, the point gets replaced by a sphere or a circle at rendertime - which is geometry. Their size is determined by pscale, so if you would set that to zero - ie giving you just a point in space - it will render nothing. Or just a Null object if you will, which is also just a point in space but don't actually contain any geometry (even at rendertime).

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Well, it's kinda fascinating, this whole subject. Like a primitive (as in polygon) in XY not existing in Z, to the point where you can't select it in the Houdini viewport as it has no surface to select. But you can select it's edge, because that's a definition. I'm just glad I'm in Sweden and not Colorado, imagine getting into this high on pot. xD

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Curves also need some width given to them as well, otherwise they'd be in the same boat as points - invisible

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Well, they have a default width in Mantra, as points have, but as you said before, width a 0 width or pscale, it won't render. I'm well aware...

My question had nothing to do with anything practical in Houdini, though, I was phrasing a statement about points when I started thinking about what they actually were, in regard to nomenclature - or rather, what constitutes geometry, if you turn it around. I'm in preparation for doing some more stuff as the thing I wrote for Gridmarkets, so that's what this was about.

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Sounds overall that you'd like mathematics, not school maths, but proper mathematics, as none of this is strange from that point of view

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I supposedly was an engineer, at least on paper, some 20 years ago. Though I think I had forgotten most of the math, material mechanics, etc, after a decade of not using it much. Getting into Houdini these last 1-1/2 years has been a fresh start for sure, in regard to math. That being said, I still believe having renovated a couple of old Land Rovers was the best prep for Houdini I had.

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For me points, without primitives, (specifically houdini points) are data carriers.

You can directly output them with the Houdini Engine plugin for instance,

using them for particles, pointcloud search data, instancing and much more

but to call them geometry or not sounds more of a philosophical question, than a really practical one
(I thought your virus point was amusing and on point for this reason :P)

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I think a point is not geometry - it's just a location (a P(osition) attribute), only if it carries other attributes that are related to geometry (pscale etc) then it's geometry.

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24 minutes ago, acey195 said:

For me points, without primitives, (specifically houdini points) are data carriers.

You can directly output them with the Houdini Engine plugin for instance,

using them for particles, pointcloud search data, instancing and much more

but to call them geometry or not sounds more of a philosophical question, than a really practical one
(I thought your virus point was amusing and on point for this reason :P)

Well, not as much philosophical as me wanting to use the correct nomenclature, talking about these things. As for points as practical, I think I got most of that covered, I started messing with particles and point clouds in Softimage 3.x, damn, those were the days.

9 minutes ago, michael said:

I think a point is not geometry - it's just a location (a P(osition) attribute), only if it carries other attributes that are related to geometry (pscale etc) then it's geometry.

You think? With that title, you just state a yes or no and that is law.

But you say it just has a position, then I wonder, is the default point render in Mantra, that if you pipe in a point without attributes, it uses a preset, or are there hidden intrinsic attributes attached to it at creation to set that?

Edited by Farmfield

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I don't know what mantra is doing under hood, but my guess is that it's detecting a point and adding a hard coded 'something' - I bet we could change it to a teapot if we wanted

If we didn't do that I'd bet it would just render nothing (as it should).

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I phrased that really badly, over complicating it. The question was as simple as, are the render attribs for points and lines on them or is it presets in Mantra - and I thought it was in Mantra. Sry.

But thanks, guy's, not the most important thread from a practical standpoint, but it's just nice to know the border between primitives and geometry, which is kinda what the answer to the question was all about.

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