Re: NURB patch documentation error

[Bruce D. <ba...@ds...>]

At 2:53 PM -0700 8/27/04, James W. Walker wrote:
>It looks like the documentation of TQ3NURBPatchData is wrong, both 
>in QuesaGeometry.h and in the QD3D manual.  I thought I'd mention it 
>here before changing QuesaGeometry.h, just in case I am 
>misunderstanding something.
>
>The description of the uKnots field says "Array of knots in the u 
>parametric direction.  The number of these knots is the sum of 
>uOrder and numColumns.  The values must be nondecreasing."  That 
>implies that numColumns is the number of control points in the u 
>direction. But the description of numColumns is "Number of control 
>points in the v parametric equation.".  So, at least one of these 
>must be wrong. I've come to the conclusion that the descriptions of 
>numRows and numColumns are swapped.  That seems to be consistent 
>with the NURB patch example in Geom Test.
>--
>   James W. Walker, ScriptPerfection Enterprises, Inc.
>   <http://www.write-brain.com/>
>

Last year, in the process of working with Yotam Gingold on a NURB 
bug, I thought that the row and column definitions were reversed.   I 
had provided an example where there were 3 "rows" and 58 "columns", 
but in order to render the NURB curve correctly I had to set numRows 
to 58 and numColumns to 3.  Here is his answer:

>I re-read the QD3D documentation regarding rows and columns, and I believe
>what you think is "reversed" is actually correct.  To QD3D, your model's
>controlPoints[0-2] are the first row, [3-5] are the second row, and so on.
>Thus there are 58 rows and 3 columns.  It is good to know then that QD3D
>is "correct".

I think my misunderstanding had to do with thinking the 2-D array of 
control points was stored as a 1-D array in column major order 
instead of row major order.

Bruce