[Sidefx-houdini-list] Access nurbs parametric uvs

François Duchesneau sidefx at trinix.ca
Wed Jan 16 10:46:12 EST 2008


I still don't understand.

I create a nurbs grid followed by a Texture Sop set to Rows and Colums, 
followed by a Scatter Sop.

I create a point aside followed by a Vop Sop containing an Open and 
Filter Point Cloud that point to the uv attribute on the Scatter Sop. I 
append a Point Sop to the Vop Sop network and use primuv having the uv 
attribute retrieved from the Vop Sop and it points to a Twist Sop I 
branched out to the initial Grid Sop.

What I've got is the point following the grid when it deforms by the 
twist BUT it still follows a uniform uv and not the one primuv is expecting.

Maybe we're not using it for the same purpose. In my case it's pretty 
fast because even if I've got a fair amount of point on my grid (500 
000), the calculation with pointdist() is done only for that point.

However I'm interested to understand what you mean because I don't 
understand you solution. Give me more details if you have time but 
otherwise consider the problem solved.

Thanks a lot.

François

Spencer Lueders wrote:
> You could create a uv texture SOP and set it to Rows and Columns which will lay out your nurbs surface parametricly.  Once you filter that in your PC and get the uv location, you can add a point SOP and and wire in your texture UVs into the second input and do a $MAPU2, $MAPV2, $MAPW2. 
>
>
> ----- Original Message -----
> From: "François Duchesneau" <sidefx at trinix.ca>
> To: sidefx-houdini-list at sidefx.com
> Sent: 16 January 2008 09:41:03 o'clock (GMT-0500) America/New_York
> Subject: Re: [Sidefx-houdini-list] Access nurbs parametric uvs
>
> At first I wanted to use a point cloud too but I thought it was going to 
> give me the texture uv attribute.
>
> What is the parametric uv attribute in the Vex/Vop world? It has to be a 
> difference somewhere because in other cases one might need the texture 
> uv and not the parametric one.
>
> François
>
> Spencer Lueders wrote:
>   
>> I recently needed to do the same thing where I used the pointdist() expression to get the uv position but I was using this on ~300k points which took about 30 min to calculate.  
>>
>> I ended up using a point cloud to get the uv position instead and it droped my calculation times down from 30min to about 1 min.  So if you are using loads of points I would recommend a point cloud.
>>
>>
>> ----- Original Message -----
>> From: "François Duchesneau" <sidefx at trinix.ca>
>> To: sidefx-houdini-list at sidefx.com
>> Sent: 15 January 2008 21:56:53 o'clock (GMT-0500) America/New_York
>> Subject: Re: [Sidefx-houdini-list] Access nurbs parametric uvs
>>
>> Thanks to FrankFirsching on the odForce forum who answered my question 
>> one year before I asked it ;)
>>
>> Now it works with the expressions pointdist combined with unituv.
>>
>> François
>>
>> François Duchesneau wrote:
>>   
>>     
>>> Hi, I'm trying to do my own curve projection on a nurbs surface because 
>>> I cannot make the Project Sop to work. It always breaks my projected 
>>> curve in many segments.
>>>
>>> What I need for that is access the parametric nurbs uv that correspond 
>>> to the isoparm because uvprim expression is reading that, not the 
>>> shading uv. Is there an operator that creates that or is it a global 
>>> variable?
>>>
>>> François
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