Subject: Re: Spline tutor in Exploring 3D
From: Adam Ives chrystie <[email-masked]>
To: James Brooks <[email-masked]>
Cc: [email-masked], [email-masked]
Date: Wed, 30 Aug 1995 00:34:46 -0700

At 09:54 PM 8/29/95 -0700, you wrote:
>Hi all,

>I have never used spline patch because I do not understand how it truly 
>works.  I was hoping the book would give me an idea what to do but just 
>when I get to activate the PATCH I get "curves do not cross correctly".
>I have tried to add more points, removed the points, different order of 
>selecting the curves and I still that same error.
>

  here is the basic idea behind splines..

a patch is made up from three or four SELECTED curves. these curves MUST
overlap eachother and also must form a CLOSED area..the best way to assure
that the cirves overlap at some point is to either use MERGE points or WELD
if the points are not perfectly on eachother...

so let's say you had the most basic spline cage...three curves forming a
triangle

        /\   Z  TOP VIEW
       /  \      EACH CURVE IS MADE WITH THREE POINTS at least! WHY? two
----     pointed curves do not bend well....you'll need bendable curves for
later..when u get better.
X

  ASSUME that the end points of each curve overlap in the diagle..and i used
merge...ASSUME all points Y=0

when patched we will get a flat triangluar shape with many subdivisions and
all having y=0

if we select a point and raise it to y=5 and keep all other points at
y=o..then the patch will be triangluar in shape...BUT it will slope smoothly
from y=5 to y=0 and keep the triangular shape...

phew i only have one hand..the other is in a cast..so i am feeling the wrist
cramp up now :(...i hope this has hel;ped...there are some more things to be
known about splines...but this should set you offf :) If you have questions
feel free to email me...i too have been busy kicking the shit outa splines
:) and getting kicked in the rear by them at times.. 

Adam Chrystie [email-masked]
University Of California at Santa Cruz
Cinema/Video Major / Senior Status

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