How do I draw this polygon?


#1

Hey guys, I’m just starting to use Sketchup and I need help drawing this. I tried quite a few things but can’t quite get this. The measurements are in meter and this is all the data I have.


#2

Use the Line tool and start drawing. Draw a line in the correct direction, let go of the mouse and type the dimension. Hit Enter and then move on to the next line.

There’s either something wrong with some of your dimensions or there are some angles you need to know before you can complete the shape correctly. If the linear dimensions are all correct, at least some of the angles must be other than 90°.


#3

And before you begin drawing, choose a template for meters, then choose File > New

… or Window > Model Info > Units
and switch to decimal meters.


#4

Hi, are those all 6 sides proportionate to my measurement? I certainly can draw something with the pencil but I’m looking to draw this with correct measurement. Can you send me the file if it is with correct measurement?


#5

You can draw with a pencil and then label the sides with any numbers you like, but that doesn’t mean they are actually that long! As @DaveR pointed out, the values you give can’t be for right angles at the corners because the lengths don’t add up:

8 + 3.7 != 10.7
13.95 + 3.25 != 16

Someone please correct me if I am wrong, but I think using only the lengths you can create a whole family of different polygons with those lengths for the sides. You need more info to nail it down to just one.


#6

You need angles, without them it is all theoretic. Even just one definite right angle might get you there.


#7

I drew each line to the dimensions you provided. If your dimensions are correct, my drawing was correct.The dimensions shown in my screen shot are measured off the lines.

It’s such a simple thing to draw, I didn’t keep it.

I think there would be an infinite number of shapes with the same lengths. Some angles are also required.


#8

Well, that’s my problem. Two sides are not equal. If it was equal, i would have just drawn a rectangle and then measure the needed segments.


#9

When measuring anything you need to establish the relative angles.
A few diagonal dimensions would do this for you.
You could then create the triangles needed to make the 2d plan in steps, as you actually measured it.

The various dimensions you show are not very ‘accurate’ - i.e. they seem to be to the nearest 100mm [4"].
It is usually possible to measure anything of this size to within about 10mm [1/2"]…


#10

What if I have this? All sides of the traingles that make up the polygon.

The thing is I got a ‘land surveyor’ to measure the land and he doesn’t know how to get the angles. I am just trying to plan something on this land and I am having this on sketchup up with exact measurement.


#11

A surveyor does not know how to compute angles given all sides ? :rolling_eyes:

… or …


#12

In manual drafting, you would use a compass and draw construction circles from both ends of a single side. The radius of each circle would be the length of the two other sides. Where the circles intersect, is the 3rd vertex of the triangle.

You would then repeat the process.


However, SketchUp does not have true circles, it uses many-sided polygons to approximate circles.

I believe that @slbaumgartner wrote a plugin to plot the intersection of virtual circles ?
(This will serve as a ping, so he can weigh in if his extension could be used in this situation.)


#13

I believe you still need at least one defined angle. Without that you still have multiple possibilities.


#14

Yes, my Circle Intersect extension, available on SketchUcation, was designed to solve triangulation problems such as this. TIG’s true-tangents can also handle it as, if I recall correctly, can on of Fredo6’s tools.


#15

True in a pure math sense because circles usually have two points of intersection (or none, or one if they are tangent), but easily resolved by a person who can see which of them to choose in each triangle.


#16

This is true. One must start with 1 side drawn at some orientation. It looks like the 8m side at the bottom is aligned with the horizontal X axis. That would be fine for beginning. After all sides were drawn, they could be grouped and rotated to another alignment.

P.S. - By default the Y axis in SketchUp is assumed to point North. In the Pro edition you can use the Solar North extension, to change this.


#17

But that is an assumption with no external evidence. It’s a sketch on paper.
Personally I would sack the surveyor.


#18

Here you go:

triangulation.skp (22.1 KB)

Edit: Dan’s point that it could be rotated to any angle around the blue axis is valid, so if this is for survey at least one direction is needed. I assumed the 10.7 side was aligned with the red axis.


#19

No it is a way to begin, and then worry about the orientation later by rotating the group.
Of, course he could begin with the leftmost side, and draw it along the Y axis. (Or he could begin with any other side.)

It doesn’t matter until he wants to orient what ever construct he will be modeling upon the plot. That construction model is what modelers want to align with the axis (normally.)


#20

I don’t think the land surveyor had taken in account for heights , as well…