[Sidefx-houdini-list] First question to the list

David McBride david00289 at yahoo.com
Wed Mar 10 05:02:56 EST 2010


Hi Alex, 
The Iso Surface surface node generates an isometric surface from an implicit function.  So you don't necessarily have to go back to trig and parametrize, actually there are a lot of parametrizations already done out there on the web.  Check out these guys:
http://www.freigeist.cc/gallery.html
http://www.oliverlabs.net/view.php?menuitem=160
http://www.algebraicsurface.net/




________________________________
From: Alex Czetwertynski <alex at franktheplumber.com>
To: sidefx-houdini-list at sidefx.com
Sent: Wed, March 10, 2010 4:14:42 AM
Subject: Re: [Sidefx-houdini-list] First question to the list

Thanks Andrew

I was not able to get the formatting right, even by copy pasting into  
a text editor (I'm on a mac...), but I just recreated the network  
based and it worked fine.

My knowledge of mathematics is probably too basic to understand  
exactly what is going on, as I was trying to figure out how I could  
plug the following cartesian equation
(y4 - x4 + a y2 + b x2 = 0)
into a similar setup, but have to admit I have no idea.  Will go back  
to Trig 101 before I keep asking questions about this....

Thanks for your help, at least I now have a nice Lituus curve!

Alex

On Mar 8, 2010, at 6:16 PM, Andrew D Lyons wrote:

> This site is using mostly polar coordinates. Houdini uses mostly
> cartesian coordinates:
>
> http://en.wikipedia.org/wiki/Polar_coordinate_system
> http://en.wikipedia.org/wiki/Cartesian_coordinate_system
> http://en.wikipedia.org/wiki/Polar_coordinate_system#Converting_between_polar_and_Cartesian_coordinates
>
> In any case to model something like this in Houdini you to set up
> extra points to sample, and then do a conversion to cartesian as you
> go. Take a look at the point SOP in this network: (Drop this script in
> a textport in Houdini - watch out for line wrapping from the email:)
> ---------------------------------------------------------
>
> # Automatically generated script: Monday March 08, 18:11
> \set noalias = 1
> set saved_path = `execute("oppwf")`
> opcf /obj
>
> # Node Lituus (Object/geo)
> opadd -n geo Lituus
> oplocate -x 3.69 -y 0.286303 Lituus
> opset -S on Lituus
> opparm Lituus use_dcolor ( off )
> chautoscope Lituus +tx +ty +tz +rx +ry +rz +sx +sy +sz
> opset -d on -r off Lituus
> opexprlanguage -s hscript Lituus
> opcf Lituus
>
> # Node file1 (Sop/file)
> opadd -n file file1
> oplocate -x 0 -y 0 file1
> opset -d off -r off file1
> opexprlanguage -s hscript file1
>
> # Node grid1 (Sop/grid)
> opadd -n grid grid1
> oplocate -x 11.8336 -y 5.95065 grid1
> opparm grid1 rows ( 100 ) cols ( 1 )
> opexprlanguage -s hscript grid1
>
> # Node point1 (Sop/point)
> opadd -n point point1
> oplocate -x 11.8668 -y 4.82124 point1
> opparm point1  numcustom ( 1 )
> chblockbegin
> chadd -t 0 0 point1 tx
> chkey -t 0 -v 0 -m 0 -a 0 -A 0 -T a  -F 'cos(ch("weight"))*
> 1/sqrt(ch("weight"))' point1/tx
> chadd -t 0 0 point1 ty
> chkey -t 0 -v 0 -m 0 -a 0 -A 0 -T a  -F '$TY' point1/ty
> chadd -t 0 0 point1 weight
> chkey -t 0 -v 1 -m 0 -a 0 -A 0 -T a  -F '$PI *($PT/18)*90' point1/ 
> weight
> chadd -t 0 0 point1 tz
> chkey -t 0 -v 0 -m 0 -a 0 -A 0 -T a  -F 'sin(ch("weight"))*
> 1/sqrt(ch("weight"))' point1/tz
> chblockend
> opparm point1 t ( tx ty tz ) doweight ( on ) weight ( weight )
> opset -d off -r off point1
> opexprlanguage -s hscript point1
>
> # Node delete1 (Sop/delete)
> opadd -n delete delete1
> oplocate -x 11.8668 -y 3.86161 delete1
> chblockbegin
> chadd -t 0 0 delete1 rangeend
> chkey -t 0 -v 0 -m 0 -a 0 -A 0 -T a  -F '$N' delete1/rangeend
> chblockend
> opparm delete1 entity ( point ) pattern ( 0 )
> opset -d off -r off delete1
> opexprlanguage -s hscript delete1
>
> # Node null1 (Sop/null)
> opadd -n null null1
> oplocate -x 11.8668 -y 2.98478 null1
> opset -d on -r on  null1
> opexprlanguage -s hscript null1
> oporder -e file1 grid1 point1 delete1 null1
> opcf ..
>
> opcf /obj
> opcf Lituus
> opwire -n grid1 -0 point1
> opwire -n point1 -0 delete1
> opwire -n delete1 -0 null1
> opcf ..
> opcf $saved_path
>
> ---------------------------------------------------------
>
>
> Cheers
>
>
> On 8 March 2010 17:35, Alex Czetwertynski <alex at franktheplumber.com>  
> wrote:
>
>> Hello
>>
>> This is my first post, been lurking around for a while...
>> Been using Houdini for only a few months, so excuse the newbie tone  
>> of
>> this question...
>>
>> I'm interested in using Houdini to create shapes of this sort
>> http://xahlee.org/SpecialPlaneCurves_dir/specialPlaneCurves.html
>>
>> What would be the way to go about creating, say, a Lituus shape?  It
>> seems to me that the type of equation that is being used contains
>> symbols that I have never seen in Houdini, but I could be wrong.
>>
>> Thanks!
>> Alex
>> _______________________________________________
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>> Sidefx-houdini-list at sidefx.com
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>>
>
>
>
> -- 
> =======================================
> Andrew D Lyons | Digital Artist | http://www.tstex.com
> =======================================
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