2 rail fail

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 From:  Nick (BODINI)
1747.1 
Moi V1

I tried to sweep the xy (circular type) profile along the 2 xyz rails (they meet in the middle buy arent connected).
After a minute of thinking, Moi gave up (i love that it just gives up and doesnt crash!). Image below.


Copy same thing over to Rhino, 2 rail sweep it, and instant results! Image below.


So what does Moi want to get it done? 3dm attached.

thanks,
Nick

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 From:  Michael Gibson
1747.2 In reply to 1747.1 
Hi Nick - it looks like the problem here is MoI's display mesher is generating an excessively dense display mesh and consuming all available memory.

In MoI if you go to Options / View / Meshing parameters and set Mesh Angle to 20, and turn off (uncheck) Add detail to inflections, then this will complete. Actually you only have to uncheck that Add detail to inflections.

It looks like there is some kind of highly folded little lumpy thing at the top from MoI's result, that is probably what is freaking out the mesher.


Looking at your rail curves those are curves made up of 5 sub-segments (using Separate in MoI or explode in Rhino will show you those), and MoI does not do a good job with this kind of multi-segmented rail curve currently.

If you go into Rhino and use Rebuild on those rail curves with something like 30 points, and then take that now single-segment rails into MoI you will then get a nicer result in MoI.

So the main difference is that MoI is doing it as kind of 5 sub sweeps which is kind of chaotic with all the twisting around (and especially the end rail segment parts are tiny), while Rhino is doing the equivalent of rebuild/segment merge on the rails first.

I think I should be able to improve MoI's handling of this kind of multi-segmented rails, I have added it to my list of stuff to look into. But until I get a chance to work on it you will need to set things like this up with longer "single-segment" type smooth curves instead of having multi-segmented rails.

- Michael
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 From:  Nick (BODINI)
1747.3 In reply to 1747.2 
That all makes sense. Thanks for looking into it. Put it on your list of "dumb things users do that I could not even imagine". :-P

-Nick
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 From:  Michael Gibson
1747.4 In reply to 1747.1 
Actually that kind of "fuse together tangent rail segments" thing that the Rhino sweeper does tends to cause a lot of problems with 1 rail sweeps, people have been requesting in the Rhino newsgroup for a long long time for Rhino not to do that.

But I think it makes sense to do it for 2-rail sweeps which can kind of get more chaotic with trying to handle multiple segments on an segment-by-segment basis.


Here's an example of when MoI's "treat segments separately" approach for 1 rail sweep yields a better result.

Here is a multi-segment curve made up of lines and arcs:
(curves attached as sweep_1rail_fuse_test.3dm)



If you do a 1-rail sweep of this in MoI, you get this result:



Each segment in the rail curve created one surface in the result object, you can then do stuff like Edit/Separate to break out one piece and do some work on it like trimming it, etc...

Here is what this MoI geometry looks like in Rhino so you can get an idea of the surface structure:




Now if you use Rhino to do that 1-rail sweep, you will get this result instead:



There are several problems - the object is one great big surface and can't be easily exploded into individual parts. Also you can see from the wireframe that the surface is more complex at the joint areas, it doesn't come to a kind of crisp clean end at each joint, they kind of blur together. There is some asymmetry to it, the surface does not have the same kind of uniform density throughout even though the originating rail structure was very uniform.


So it was to avoid this problem that I made MoI's sweeper work on a kind of separate segment-by-segment basis instead of trying to fuse things together.

But in your 2-rail sweep case, fusing things together is what makes a better result there, it is just not as straight-forward for 2-rail sweep to try and treat it on a segment-by-segment basis, I think I will try to do the fusing for 2-rail sweep but leave it as the non-fused method for 1-rail sweep.

- Michael

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 From:  Michael Gibson
1747.5 In reply to 1747.3 
I have a fair number of sweep things to fix up in v2, so I have put this with those other sweep stuff on my list.

- Michael
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 From:  BurrMan
1747.6 In reply to 1747.5 
Help for amateure!

I was looking at the first post in this thread. trying to re-create the rails he used.

to draw these would you do it by using the different viewports "while" drawing?

sorry for the 2d brain. one quick explanation from someone and then I can experiment and figure it out.

The only way I could figure out to draw them was to click in front, move to 3d and go up in z-click, move to top and cross over-click. Does this make sense and am I on the right track? or is there something I should look at as to not develope bad learning?

Thanks for any input,
Burr

BTW: I was also trying to create his sweep by creating a second profile and then rotating it to get the twist (a scaling rail to get the shape). I was getting some results but seemed like alot of work to do what he did simply. Michaels solution made it work.

The blob at the top was interesting. I tried to delete some of the points from within MoI and it changed the topology of the top surface. I dont have rhino to do what the suggestion was. is there another generic explanation so I may know how to apply it with some of the other apps I have?

EDITED: 5 Jul 2008 by BURRMAN

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 From:  Michael Gibson
1747.7 In reply to 1747.6 
Hi Burr, probably instead of drawing something like that all in just one shot of the Curve command, it is easier to draw a planar curve to start with, and then turn on control points with Edit/Show pts and move them around.

Once a point already exists, it is just a bit easier to reposition it by dragging in a different view, or using rotation on it, etc... Undo works a bit easier for that, because you can undo a small tweak instead of undoing the whole last point which is what will happen in the Curve command.


It's not a bad exercise to do it all in one go of the Curve command and it is possible, but typically I would recommend that kind of stuff for only a small number of points like if you are going to draw 3 or 4 points, and you know you want a specific arrangement with stuff coming up in z, etc.... - then you can drag out some construction lines to track in z but it is rather tedious to do this with more than about 4 points or so.

Also with adjusting control points afterwards, you may want to get the Nudge command from Petr's page here: http://kyticka.webzdarma.cz/3d/moi/ - that will enable you to use some keystrokes to move a control point (that you turned on with Edit/Show pts) a small amount in x,y, or z.

- Michael
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 From:  BurrMan
1747.8 In reply to 1747.7 
Thanks Michael, That is great stuff. I'll mow over his scripts more later.

The Shortcut keys are stored in the ini file. My V2 has an ini file in the root directory and it stored them there. (this could be my doing) Is the ini compatible for me to just copy it to the V1 root, (or the app data folder)?

I was moving them around to facilitate the usb install.

Thanks,
Burr (Just call me NURBS)
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 From:  Michael Gibson
1747.9 In reply to 1747.8 
Hi Burr, yes by default the moi.ini file will go to a central location (in XP it is: C:\Documents and Settings\Michael\Application Data\Moi\moi.ini ).

But when MoI starts it will look for any moi.ini that you may have copied into the same folder as MoI.exe and if it finds one there it will use it instead of the shared one. (this is what you would normally set up to run off of a USB drive).

So if you want to have a particular installation use different settings than another one, that is one way to do it. You can also pass the path to an .ini file to MoI.exe as a command line parameter to make it use a specific one.

The v2 and v1 .ini files are compatible, you can copy them back and forth to one another. The v2 one will write some additional stuff to it, but that's ok those extra new things will just be ignored by v1.

- Michael
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 From:  BurrMan
1747.10 In reply to 1747.9 
Happy 4th. :)
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 From:  Nick (BODINI)
1747.11 In reply to 1747.10 
The rails were a helix on the side, a flat helix on top and projected onto revolved surface. The revolved surface was a cylinder with a domed top, and a fillet around the edge.
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 From:  BurrMan
1747.12 In reply to 1747.11 
Thanks Nick,
Thats a way to get odd yet precise curves. Thanks. I also tried just drawing it. I could, yet wasnt sure how to be precise or if my thinking was the best way. Both yours and Michaels way were great help to me in my learning!

Thanks,
Burr
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