Follow-up question, set the EXACT line length of a triangle side

Yesterday is posted this question which has been mostly answered. Thx for all the help. I have a follow-up question though, hopefully someone can help me.

As follows, I need a triangle with the following dimension: 6.00m, 3.00m, 5.00m.
I draw the 6m line (A), followed by the 3m line (B) and finally add the last line ©.
By rotating line B (rotation point AB) I want to give Line C a length of 5.00 meters.

However, when changing the decimals (or looking at the entity info panel) i see the line is not 5.00m but 5m and then some.

Is there a way to set the rotation (AB) so that line C is exactly 5 meters?
I tried different snapping methods, but even without snapping ( and a steady hand :wink: ) 5.00 meters seems impossible.

Help is much appreciated!

You could only get Line C to be exactly 5 if you know what angle c is and rotate Line B to that angle. Just use @slbaumgartner’s plugin to identify the corner, draw the triangle, and get on with your modeling.

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Thx DaveR,
Just to be sure, there’s no way to work the other way around, ie: set line C to 5.00 where corner AB is updated accordingly?

You mean the Circle Intersect v1.0.0 plugin i assume?

Yes. Do you mean that you still haven’t tried it?

once you get it ‘nearly right’ re-use the tool and type angles e.g .005 and watch the length change…

you can adjust to the six decimals this way…

EDIT: this one needed an additional 0.04595˚

but it’s easier with a plugin…


Hi DaveR, I did and the plugin works like a charm, however, I assumed (should stop doing that) a tool like SketchUp simply has such a feature out of the box. Especially when used in architecture where lengths and corners are accurate.

That being said, I also need the non-plugin way as I do not always have access as an admin to install plugins (I use sketchup for multiple companies, all running on their computers, non network).

John, thank you for the tip. It is indeed more time consuming but a great solution when no plug-in is at hand.

Thx both, case closed…really :wink:

You ought to go out an measure some architecture. If that’s your standard, set Precision to nothing past the decimal and you’ll find you can get the lengths close enough.

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I wonder if Didier Bur’s Trilateration plugin still works. Can be found at Sketchucation. Didier’s old Ruby Library Depot website seems unresponsive.

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I think I know how you wish it would work. You’d like it to work like this:

(I made a video, but I’m not getting it to upload)

Once imported into SU, it comes out like this, losing the accuracy in the arcs in the process, but the triangle is correct.
3,5,6m triangle fr PowerCADD.skp (137.4 KB)

Do you have a tape measure and protractor with that kind of precision?

I don’t normally have the units set that far out, but I thought I’d see if any error could be seen creeping in.

I do use a Leica Disto when I measure existing buildings. It’s good to about 1/16" or better. I usually round to 1/8" or 1/4" and idealize minor amounts of out-of-plumb and out-of-square-ness.

Someone told me the Army Corp. of Engineers has a motto: “Measure it with a micrometer, mark it with a grease pencil and cut it with an ax.” I always liked that.


Awhile back there was a guy who was complaining because he couldn’t draw his SketchUp model with more than six places beyond the decimal in millimeters. This was for an object he was going to 3D print. He had no tools with which to measure that precisely and the dimensional tolerance of the printer was much coarser than that. It’s just a waste of time and energy to chase that kind of precision in that application. A sure way to make yourself crazy.

Me too.

“I re-cut it three times and it’s still too short!”


Me too,as well. @discobot

This provides some more good inspiration.

Trias follow the inequality rule and once you have the sequence of sides the law of cosines can be used to check you results; A+B>C;B+C>A;A+C>B and must be satisfied for all three conditions of the sides

Register (free) at SketchUcation …
Then download Trialeration from the SketchUcation PluginStore

Trilateration v1.1x SketchUp plugin by Didier Bur

User Guide: Trilateration.pdf (114.6 KB)

Example Model: 3-5-6_Triangle.skp (21.5 KB) … Time to complete, ~15 seconds

The simplest way to construct this triangle is to draw the baseline to the required length (6), then from one end draw a circle with radius of 5, and from the other end draw a circle with a radius of 3. The point of intersection of the circles is the third corner of the triangle. Of course, then you fall prey to the not-really-a-circle syndrome, but if you bump the number of segments up real high you can still achieve reasonable accuracy.

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@mac7595 please don’t do that in a thread.
Do it in a PM

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