[Sidefx-houdini-list] pcfilter point number

mdunkley at gmail.com mdunkley at gmail.com
Wed Aug 3 14:32:25 EDT 2011


Hey Nick -

I've had some fiddly problems using pcfilter for point numbers in the past.  
I was attempting to create a float point number variable called ptnum and  
just look it up with no interpolation (ie 1 point lookup) from pcfilter,  
but even then i would often get incorrect values - I think the filter is  
doing some kind of filtering no matter what. Sometimes the ptnum value it  
returned would just be a number off, as if it was getting ceil'ed or  
floor'ed, some times it came back with a floating point component, so  
clearly there was some sort of interpolation happening.

I can say for sure that the other method you mentioned *does* work.  
Pciterate doesn't really do anything on its own - you need it to feed a  
while loop (both ouside the loop, and then again on the inside). Within the  
while, you can then use pcimport with "point.number" / "point.distance" to  
pull all that info out. My impression of pcfilter is that its just a quick  
and dirty one-stop-shop way to slew values between points, not to intended  
to work with the other point cloud functions - if you need to do anything  
very specific you'll have to roll your own with pciterate and a while loop.

If you haven't seen it, check out peter quint's point cloud videos on vimeo  
- the second one talks very specifically about some of the issues related  
to making your own:
http://vimeo.com/9108284

Best,
Mike


On , Nick van Zutphen <nvanzutphen at live.com> wrote:
> I like to stay close to 'SESI' guidelines, or like the default tools work  
> (something I inherited from my intenship). I guess giving a position  
> vector, which can also be set by using a handle is pretty close to that.  
> Obviously using a sphere would work, but it's not very neat, is it?



> Cheers,

> Nick van Zutphen



> --------------------------------------------------

> From: "Alvaro Castaneda" varomix at gmail.com>

> Sent: Wednesday, August 03, 2011 6:21 PM

> To: sidefx-houdini-list at sidefx.com>

> Subject: Re: [Sidefx-houdini-list] pcfilter point number




> This might be a dumb idea, but why don't you

> ask the user to place a sphere for initial position

> use that to grab any points inside and start from there?



> I can use that :)







> 



> *.:varomix:.*

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> On Wed, Aug 3, 2011 at 10:06 AM, Nick van Zutphen  
> nvanzutphen at live.com>wrote:




> Hi!



> I finally figured out how this maillist thing works :-), at least I hope

> so. It feels a bit like 'you're used to Internet, and you have to use 'the

> wire', telex or how ever it's called in English' ;-).



> I'm working on a tool which operates on scattered points and it needs a

> starting point. I would like to give the user the ability to specify a

> position vector and the tool will figure out what the closest point is.  
> This

> becomes need when you would like to start in a certain area and the points

> might change due to a different seed or what so ever.



> I think of a pointcloud method, however I'm interested in the closest  
> point

> pointnumber. I know pciterate has the option point.number but that doesn't

> seem to work on pcfilter and ptnum doesn't give any luck either. I would

> like to use pcfilter since it's about a single point and iterating over 1

> point doesn't seem to make much sense.



> So my question is: 'Is there a way to get the point number when using

> pcfilter. If not, what's the alternative?'



> Cheers!

> Nick van Zutphen

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