 # Command: _MatchSrf https://docs.mcneel.com/rhino/6/help/en-us/commands/matchsrf.htm

Match Surface Options

Curvature __ percent
Curvature matching, in percent of the radius of curvature.

I’m trying to understand what the percent option means.

For example: curvature is default 0.05 percent

(A) Radius = 20 mm : The CURVATURE VALUE ( 1/Radius) would be 0.05
(B) Radius = 50 mm : The CURVATURE VALUE ( 1/Radius) would be 0.02

0.05 - 0.02 = 0.03 < default 0.05 percent
Thus, The two surfaces would be 100% curvature continuous?.. No?

-Pascal

Pascal,
I’m I correct in saying that all these settings are meaningless unless you have the “refine” option set.
In other words, if you don;t have “refine” set you are going to get the same result no matter what numbers you fill in the boxes.

It is very difficult to understand what it means. Hi jim - I believe that is correct, yes. I have not actually tested though, in all these years of using it… I’ll see if I can come up with a meaningful test case.

-Pascal

Hi Knead - The radius of curvature of the surfaces should be the same to within that % at points along the matching edges.

-Pascal

for example:
20 mm VS 50 mm

Thus, 40% = Maximum difference in curvature between surfaces.

Does the percent mean to compare the physical size of the radius (20mm and 50mm), not the values of the curvature (1/radius = 0.05 and 0.02)? right?

The percent difference between 0.02 and 0.05 would be
100*(0.05 - 0.02)/(some measure of the general size of 0.02 and 0.05), for example
100*(0.05-0.02)/0.05 = 60%. Whether you use, the radius or the curvature the answer is roughly the same. in attached file:

100 * (81.5069601 - 81.4166767) / 81.5069601 = 0.1107677183509633 %
When comparing Radius size in%, Matching tolerance exceeds 0.05%. or

1 / 81.5069601 = 0.012268890887025
1 / 81.4166767 = 0.0122824959275205
100 * (0.0122824959275205 - 0.012268890887025) / 0.0122824959275205 = 0.1107677183512528 %
When comparing curvature in%, Matching tolerance exceeds 0.05%. Thus, the radius or curvature of the matching surfaces have not the same within tolerance 0.05%. What’s wrong with this? The Curvature Difference Method.

Curvature Deviation = Curvature (Blue) - Curvature (Red).
Curvature Deviation = 1 / Radius (Blue) - 1 / Radius (Red)

In the attached file,
Curvature Deviation = 1 / 81.5069601 (Blue) - 1 / 81.4166767 (Red)
= 0.012268890887025 (Blue) - 0.0122824959275205 (Red)
= 0.00001360504049546093
= 0.00001360504049546093 * 100
= 0.0013605040495461 percent

Thus, 0.0013605040495461% is the same within tolerance 0.05%
Right? !

Sorry, I was just pointing out that in your first example, with 20 and 50, your calculation was incorrect.

in attached file:

100 * (81.5069601 - 81.4166767) / 81.5069601 = 0.1107677183509633%

I thought the result of the matching surface should be within tolerance.

0.1107677183509633% > 0.05%

But, When comparing Radius size in%, exceeds 0.05%.
What’s wrong with this?

Is your problem in the numbers, or is there something wrong with your model?

Command: _MatchSrf
and
Check Refine match option.
Input Curvature 0.05 % percent

But, The radius of curvature of the surfaces was not the same to within that 0.05% at points along the matching edges.

Yeah, something isn’t right. We’ll look into it. I’m not sure this is a very good measure of accuracy.