Vertices Number

[Arthur Spooner]

Correct me if I'm wrong, 0:1 which is point number 4 in the spreadsheet correspondence to that on the geometry ?

 

I'm trying to understand how to read the numbers for each point  ? I understand that I'm seeing the vertex numbers around the point, how does this help ?

Edited March 29, 2016 by Arthur Spooner

[mestela]

Yes you read that correctly, prim0:vertex1 = point4 in that image.

 

cyan is the point number. point numbers are unique, you'll never see a point number reused.

 

pink is the prim number. these are also unique, they won't be re-used either.

 

green are verticies. verticies belong to prims, so you'll definitely see them reused. a way to read the '2:5' thing is to say 'the 5th vertex of the 2nd primitive'.

 

verticies 'follow' the position of points. in the dodecahron gif towards the end, you could say 'the 4th vertex of the 2nd prim follows point 7'.

 

in the geometry spreadsheet, that would be listed as 2:4, and the point would be 7.

 

 

All this is a little academic to be honest, for the most part you rarely manipulate verticies directly. Two notable exceptions are normals (they usually get applied to verticies, so that you can cusp edges), and uv's (so you can have seams on your uv's).

Edited March 29, 2016 by mestela

[Arthur Spooner]

In the following image we are looking at, prim0:vertex 1 = point ?

 

The point number makes up or creates the hexagon shape, correct ?  

 

Point numbers and Prim numbers can never be reused in Houdini, for whatever reason, they are, static in a way ?

 

green are verticies. verticies belong to prims, so you'll definitely see them reused. a way to read the '2:5' thing is to say 'the 5th vertex of the 2nd primitive'.

 

 

Using the image above, in the Geo spread sheet, it is Point Number 1, 0:4 so that would be expressed as; the 1st vertex of the forth primitive ?

 

verticies 'follow' the position of points. in the dodecahron gif towards the end, you could say 'the 4th vertex of the 2nd prim follows point 7'.

 

 

I don't understand, because I'm still hung up on the fact that vertices and points are one in the same, now I'm learning they are not  Why in every corner of, for example the image I posted in this post, is there three numbers around the point, I know they are vertices, but that is what I'm stuck on, the difference and that they can be reused while every other part of a piece of geometry cannot, regardless what the geometry is.

[mestela]

Feels like we're going round in circles here, you might need someone else to help, I don't think I can explain any more low level than this.

 

Maybe a video tutorial would help, try this: https://vimeo.com/6190040 

[Arthur Spooner]

I'll watch the tutorial, I hope it answers some of my recent questions, I want to understand this. 

Edited March 29, 2016 by Arthur Spooner

[Arthur Spooner]

I think I understand, as in the platonic, the image below; makes up one face of the platonic, five vertices, makes one polygon as shown in the Geo spreadsheet ?

 

What I don't understand mestela is how you reconstructed the platonic knowing exactly where to place the next primitive, I hope that is the correct way to describe it ? 

[mestela]

Yes, that image capture there shows primitive 0, that has 5 verts, made by connecting points 0 1 2 3 4.

 

I didn't recreate the platonic knowing where to place the next primitive. I had a blast node that deleted all but 1 of the primitives, then left 2 primitives, then 3 etc.

 

click to play

 

I thought of another analogy that might be useful/dangerous. You could think of it as one of those nails+string pictures:

 

http://cf.bydawnnicole.com/wp-content/uploads/2015/09/initial-string-art-final.jpg

 

Say you had a bunch of points like this:

 

 

You take your string, and wind it around points 0, 1, 4, 3, 0. You've now defined 1 primitive:

 

click to play

 

The order in which you visited the points is stored on the verticies.

 

You take a second piece of string, and this time visit points 1, 2, 5, 4, 1:

 

click to play

 

Again, the order that you visit the points is what the verticies represent. 

 

Because both pieces of string visit points 1 and 4, if you move those points, both primitives will stretch along with them.

 

click to play

Edited March 30, 2016 by mestela

[Arthur Spooner]

Yes, that image capture there shows primitive 0, that has 5 verts, made by connecting points 0 1 2 3 4.

 

I didn't recreate the platonic knowing where to place the next primitive. I had a blast node that deleted all but 1 of the primitives, then left 2 primitives, then 3 etc.

 

platonic_blast.gif

click to play

 

Based on vertex group, whether that group is; 0,4,3,2,1 you then entered that value into the blast node ? Is this typically how you create polygons for polygonal mesh, from post #15 you use VEX and wrangler.  

 

I hope I'm beginning to understand the low level geometry within Houdini !

[mestela]

If you plan to get this low level, yes. Another way is with an add sop in primitive mode, in its default mode it visits all the points in order and constructs a single primitive, or you can tell it take every N points and connect them into prims, or prims that share a common attribute value, or groups etc.

[Arthur Spooner]

Based on vertex group, whether that group is; 0,4,3,2,1 you then entered that value into the blast node ?

 

 

For verification, this is how you made the first primitive in post #27 ? 

Or you could use VEX

 

 

It makes more sense when you start creating your own primitives in wrangles. You take your points, add an empty primitive, then add verticies to the primitive that refernce points. Eg, say I had 3 points floating in space (with @ptnum's of 0, 1, 2), I could run this in a detail wrangle to connect them up into a triangle, by first creating the primitive, then adding verticies:

int myprim = addprim(, 'poly');

addvertex(,myprim,);

addvertex(,myprim,1);

addvertex(,myprim,2);

 

How do you create an empty primitive ? Also how do you know what shape you are creating, you can create a random primitive Can you for example make a coffee cup using the blast node or VEX, if so, how do you know to make it round, and with a handle, in other words, without making primitives randomly into a mess so it comes together as a coffee cup ? 

 

Another way is with an add sop in primitive mode, in its default mode it visits all the points in order and constructs a single primitive, or you can tell it take every N points and connect them into prims, or prims that share a common attribute value, or groups etc

 

 

Can you show an example ? There are three methods, VEX, Blast Node & the Add SOP to create geometry.

 

Vertices in Houdini are different then Vertices in Maya, it Houdini Points are not vertices but in Maya, vertices and points are equal ?

[Arthur Spooner]

I don't want to bother mestela with too many questions, he has answered so much, much appreciated.  

 

If anyone wants to give some input as I'm trying to understand the theory of some aspects of Houdini workflow before I resume jumping back into exercises ?

Edited April 1, 2016 by Arthur Spooner

[Guest tar]

I would recommend forgetting about verts for the time being, mestela and anim have explained them thoroughly, as they do not come into common workflows. Come back to it when they affect your work, at which time you probably have forgotten about Maya and Houdini will seem natural

[Arthur Spooner]

I've already tasted the candy

 

What is it I'm not understanding, as in, well my my recent post asks a few more questions, well, I want to model with verts, why I started with the VEX question. I'm happy what I learned up to this point, I don't want it to go to waste.

 

Hopefully someone can take over for mestela and hopefully I begin to make sense of the spaces of what I learned.

Edited April 1, 2016 by Arthur Spooner

[Guest tar]

Why do you want to model with verts? Never heard of that, sounds like a mistake. Modelling is done with points.

[Arthur Spooner]

Vertices are considered points in Maya, for example while in Houdini points and vertices are completely different.  What makes up vertices in Houdini, as in, do vertices make points ? 

[Guest tar]

Maya vertices are Houdini points. Where do you see the difference?

[Arthur Spooner]

What are Houdini vertices ?

[Guest tar]

Houdini Vertices are an extra representation of data that Maya hides away from the user.

[Arthur Spooner]

Houdini Vertices are an extra representation of data that Maya hides away from the user.

Ohh.  Correct me if I'm wrong, vertices in Houdini surround points, just trying to understand what is shown in the documentation, hopefully you know the diagram in the docs I'm referring too off hand ?

[Guest tar]

That sounds correct - so you don't need them. If you are familiar with polygon winding orders, then the order of verts set the way normal is calculated.