How to accurately draw irregular room shapes

Hi! I’m new to Sketchup. I’m trying to figure out the best way to accurately draw the inner walls of rooms that are more or less rectangles, but with irregular measurements. I am an interior designer, so I am not trying to make super precise architectural plans—just floor plans/furniture placement plans that are accurate enough to ensure that the furnishings and fixtures I’m including fit correctly.

A friend recommended I measure the length from one corner of the room to the opposite far corner and use that as the basis for my plan. However, if I do this, how do know exactly where to place the end of my tape measure guide line? For example, let’s say corner-to-far-corner measures 5m—5m at what point on the axis?

I have attached a screenshot of a furniture placement plan I’m working on for one of the irregularly-shaped rooms for reference.

One thing you could try is my SB Trilateration extension, available at SketchUcation. All you need to know are the main sides and the diagonals. It will plot guide points at the required corners.

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@slbaumgartner Hi! I installed your extension and made sure it’s on. I started to. draw, but I don’t see anything new popping up. How do I make use of the tool?

Hello, if you know the diagonals and sides lengths, use simple geometry.
SketchUp won’t be the perfect tool for that, I’d draw it in a 2d CAD software first but if you set SketchUp circle tool at a High number of sides (enter the value and hit enter to validate before picking the circle center point), it should be precise enough.

Let’s Say your room is ABCD. Draw one of the sides, for example AB. Draw a circle with A as a center point and AC diagonal length as a radius. Draw a circle with B as a center point and BC as radius you’ll find C at the intersection of both circles.
Repeat for D

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1. Draw a rectangle as the reference plane for the trilateration (it can be any size, but best if it is large enough that the new edges won’t intersect it).
2. Draw an edge the length of the first side
3. Activate the 2D trilateration tool either via the SB Trilateration item on Extensions menu or the SB Trilateration Toolbar
4. Click on the face of the rectangle to tell the tool what plane to use. You only need to do this once.
5. Click on one end of the line
6. Type the length of the side adjacent to that end.
7. Click the other end of the line
8. Type the length of the diagonal between the second end and the far corner
The tool will create guide points at the two possible solutions (both ways from the original side). These points are accurately placed without any impact from SketchUp’s representation of arcs.

Repeat this process for the side and diagonal from the other end to get fourth corner guide point. Draw edges from the endpoints to the guide points and between the guide points to create the other three sides of the room. If your measurements are accurate, the fourth side should match what you measured.

Once you have seen how this works, it goes much faster than the number of steps would suggest!

@slbaumgartner hey I think I got it! Took two tries but now all. lines are the dimensions I had jotted down.

@slbaumgartner actually one is 12cm off but the rest are correct. I think that’s close enough—do you have any tips for getting even closer?

I think you need to recheck your measurements and possibly your drawing. Make sure length snapping is turned of in SketchUp’s units, as you want your measured values, not rounded ones. The extension solves the real equations of trilateration without any approximations, but can only be as good as the data fed to it.

@slbaumgartner ok thank you! Could it also be. related to not drawing the angle of the first wall correctly? If I draw. that as a straight line, but it’s slightly angled in. reality, would that cause an issue with the other wall measurements?

If the first wall is not straight that means you have an extra corner in the room…
That means you have to measure more diagonals and draw again…

I’m not sure whether you meant your question as @tweenulzeven took it, or meant that you drew the wall at an angle to the axes. If you just meant angled from the axes, that doesn’t matter.

But if you meant the wall actually has a bend or corner in it, that could throw off your measurements and your drawing of the walls. Trilateration requires accurate straight-line distances between points, which can be hard to get if the wall bends into the measurement line. There are ways to deal with bent walls, but they depend on the details of the bend.

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Here’s a way to place the four corners that doesn’t assume the walls are flat. It does require that you can go back to take new measurrements, however.

Place an object that is known to be straight and whose length is accurately known across the room. Exact placement doesn’t matter, This technique is known as creating a baseline for further measurements.

Measure distances from each end of the object to each corner of the room, a total of 8 measurements.

In SketchUp, start by drawing an edge whose length matches the reference object. Then use trilateration from the ends of that edge to get guide points for the four corners.

This will give you accurate locations for all the corners. Of course, unless you do something else to measure the bend in each wall, you will only get a straight-wall approximation to the real thing. But that will almost surely be good enough for the uses you describe.

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