Differences in matching methods


(Rob McPherson) #1

A lot of the time, for speeds sake, I’ll use the blendsrf command to create a nice blend between two surfaces. Most times it works fine.

But in some situations, usually when I’m blending between two surfaces which have their ends cut off at different angles, I get a nasty result from blendsurf and will then do it manually by creating a ruled surface between the edges and then matching the ruled surface with continuity back into the adjacent surfaces.

But it seems the two methods use different parameters to determine the match (see pic below).

Is there any chance we could get a consistence of match through these two commands?

Regards,

Rob.


(Rob McPherson) #2

Looking at the point distribution between the two methods, I’d say that BlendSrf needs to be re-written to emulate the MatchSrf command. Blend surf leaves too big a gap between the inner most points which creates a ‘flatter’ blend. MatchSrf seems to space the points out more evenly.


(Pascal Golay) #3

Hi Rob - Yeah, I guess the problem is going to be that MatchSrf starts with what you’ve got- if you hand it a ruled surface and ask for curvature continuity, and the other end preserved at curvature, it will change the surface degree to 5 and distribute the points evenly across before it starts working on matching. If you give it a degree 5 surface it will use the points as they are as a starting point - if they are even they are even and if more bunchy, then that is what it works with. In BlendSrf you get to monkey with the spacing to taste of course.

-Pascal


(Rob McPherson) #4

@pascal I think the problem lies with the default point spacing at a value of 1, pre any monkeying. Let me prepare a file to try and explain better…


(Rob McPherson) #5

@pascal Here you go, I’ve done the two different blending methods between the same surfaces in this file.

blend.3dm (63.6 KB)

As you say, the match command does a great job of creating equally spaced points, but the default value for BlendSrf creates a flattened middle part. This makes BlendSurf a poor command to use with default values. I’ve tried to monkey them to match and have to use the following values -


(Pascal Golay) #6

Hi Rob - Thanks - I don’t know if this is completely ‘fixable’ in some what that would always work out best at the defaults. I know that @lowell did a bunch of work to get BlendCrv to make a better default shape then the old Blend command, and it looks like BlendSrf makes the same shape here as BlendCrv. Maybe there is more room to tune…

-Pascal


(Rob McPherson) #7

Ok, thanks for looking at this Pascal. I think I’ll just avoid using the blendsrf command in future. Shame, because the other method takes lots more clicks!