 # How to draw a quadrilateral knowing edge lengths?

I know all the four lengths of a flowerbed, but no angles. How can I draw it in SketchUp?

I can draw one line with a specific length. Then I can draw the next line with a specific length, but I do not know the angle, so I draw it approximately. Then I draw the third line.

Then I tried to adjust the lines by moving the third vertice, but only the second line stays the same length (and the same angle), both the 1st and 3rd lines get their distances and angles adjusted to keep them connect to the moved 2nd line, and to keep their other (non-connected) vertices stationary.

So, I cannot move anything without disrupting the specified line lengths, which actually are what I know for sure and need to keep intact. But SketchUp decides other things to keep intact.

And this is even before I try to add the fourth line, which should eventually connect the whole shape.

So, is it even possible to draw such quadrilateral without knowing angles, or do I have to use geometry and calculate the angles, and then set specific angles when I’m drawing the lines?

You could use the Arc tool to strike arcs with the radii of the lengths and join where they cross.

1 Like

There are infinite possibilities, you have to know at least one angle.
Can you measure the diagonals?

3 Likes

Oops, I didn’t think this through. All four lengths do not define a quadrilateral really… OK, so I do not have enough measurements to draw it precisely… I can’t measure the diagonals in the near future. But if I knew the diagonals, what would be the way to construct it in SketchUp?

I could guess the approximate angles. But how do I connect 4 lines with specific lengths, but approximate angles? If I draw a quadrilateral and then try to use the moving tool (trying to move a vertex, but a side seems to be selected every time) to get it into an approximately correct shape (meaning angles), it seems to inevitably change the length of some of the edges.

FWIW, if you knew the diagonal lengths you could calculate the angles using basic trig because you’d have two triangles to work with.

2 Likes

Thanks for the image! So, I would need to calculate the angles and then draw it with SketchUp and setting those angles. Thank you!

I didn’t calculate the angles in my drawing. I was just pointing out that with the diagonals you could calculate the angles. No need to do that if you use the Arc or Pie tool.

I started with the bottom edge and from its ends, drew the pie sectors.

Oh, I see. OK, thank you for the arc tool method! I think I get the idea. I’ll remember to measure diagonals the next time in a similar case.

Only one diagonal is required.

1 Like

This topic was automatically closed 91 days after the last reply. New replies are no longer allowed.