Creating an arc with specific segment lengths
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Hi all, I am new to this forum but I have been using Sketchup for some time. I understand from using sketchup and from reading as much as I can on this forum (which is awesome by the way) that SU is limited on arcs and circles. There is actually two things that I would like to do which are both based on the same concept, hopefully I can put it into clear words.
Lets say I creat a typical random sized circle in SU which is actually 24 line segments. Typically the segments end up being more precise then SU supports which ends up using a ~ symbol to describe a minute length. I like to say this is an "unknown" length. So, lets say I want to take one of the segments of unknown length from my circle and create another circle with 36 segments that are the exact same unknown length as the 24 segment circle. I could accomplish this be copying one of the segments and then making a straight line of 36 segments, then rotating each one by 10 degrees (36x10*=360*). This is tedious and would not work very well if i wanted to create a circle with 37 segments. I want to then take this same concept to create an arc using the same unknown length segments. My thought is this: lets say I want to make an arc using 11 of those unknown length segments and I know where I want it to start and stop (chord length). I know that geometrically you can find the center and radius of a circle if you have at least two chords for that same circle, and technically in my example there are 12, but the problem is that I cant figure that out with estimated lengths, so it seems that there could be a plug in that works with SU to do the math for us. So, is there such a plug in or can it be created. I appreciate any help that you can give me.
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If you look at my 2D Tools there's a Polygon tool that lets you type in the number of sides [segments] '24s' and their individual length '300x' - calculating its radius to suit those - you then pick its 'orientation' to save it... You get 24 sides and each is 300 units long... See its Help file for more details,,,
This is the basis of you request - isn't a circle effectively a multi-sided polygon in these circumstances ?
http://forums.sketchucation.com/viewtopic.php?p=185760#p185760 -
this method may be a bit unorthodox but it works well.. (well, maybe it's orthodox but just undocumented?)
basically, remove one of the segments from the circle but don't break it or explode it.. (make sure it's still recognized as an arc by sketchup)
if you move one of the end vertices, the arc will remain a true arc.. just move the two ends to the unknown length and you're set. (put the move tool directly on the ends with no selections)
(for clarity on the video, i've used a 6 sided circle and a 12)
[flash=660,405:1nfd1fwm]http://www.youtube.com/v/7Zu8PC0Ua3o?fs=1&hl=en_US&rel=0&color1=0x2b405b&color2=0x6b8ab6&border=1[/flash:1nfd1fwm]
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so, i guess that will solve part of your questions.. the other thing you mentioned about doing this with a known chord length, 'unknown' segment length, and desired # of segments is possible as well using the same method.. (i'll make a different video showing that if needed)
the last part of your post, i'm not quite sure what you're asking but i think you're saying you can't find the center of an arc with 'unknown' (or estimated) segment length? three ways:
the first, if sketchup still recognizes the lines as an arc (if it does, the curve will be called an arc in the entity info window).. make sure you have google's example rubies called 'utilities' turned on in the extensions preferences.. right click the arc/circle and select 'Point at Center'... a Cpoint will be placed in the middle
the second way (unknown everything but at least 3 segments) can be done like this:
the third way, which eliminates the need for the 2nd way, is to use Chris Fullmer's ruby.
Exploded Arc Centerpoint Finder
found here:
http://forums.sketchucation.com/viewtopic.php?t=18963[but if i'm fully missing what you're asking for then i'm sorry
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What both of you have suggested works great for the first part: creating a larger circle using the segment length of the smaller one. But now that that is done, I need to create the arc. When I first posted this I was at work and did not have access to my drawing, but now that I am home I can show you exactly what I am trying to do. I am creating tank tracks but with only two hubs. The issue is that one hub is smaller than the other, hence the 24 and 36 sided circles. Each track has to be the same width, but now I need to copy the rest of the tracks between the tops of the two hubs. Typically the tracks have a small amount of slack that hangs down on the top part of the track, hence the 11 segment arc. I know I am being a perfectionist about it but I want it to look right. Also I would like to maybe convert it into SketchyPhysics later, so I would like it to be precise. Here is the pic of what I have so you can see exactly what I need:
So again, I am trying to make the arc with 11 segments that are all the same size as the line that the arrow is pointing to on the left hand side of the last picture (it is showing ~ 1 31/32"). The variables that I need are either the bulge length or the angles that each segment need to be from one another in order for all 11 segments to fit within the larger chord and be the same.
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