I’ve created a 2D model in SketchUp for a project. I then transferred to LayOut for labelling and dimensions as I’ve heard it’s a cleaner look from LayOut, but some dimensions are not correct. As you can see in my model, the first two (on left vertical wall) are correct but the third is saying 29mm which is obviously not correct. I did read on another thread that the model may not be sitting directly on the axis in SketchUp, but from what I can see, it is.
Your Layout viewport is showing the last saved view of your model in SketchUp. This last saved view is more or less looking down, but not perfectly flat and the camera is still set to perspective. This means that in the Layout file the view is not truly 2d.
Select the viewport, right click and choose open with SketchUp, once the model is open in SketchUp, go to Camera and choose parallel projection, then in Camera>Standard Views>top. Then save and close the file.
When you return to Layout the view will be flat and looking straight down and your dimensions should all work fine.
Best practice is to save a scene in Sketchup and associate each viewport in Layout with a scene. If you plan to have more than one view of your model in the Layout file this would be the way to proceed.
Small point of order: in SU 2020, you now have the option to choose standard Top, Right, Left, etc, views from within Layout. This is what you usually use in 2D representations. It can save cluttering SU with lots of scenes if you select them in LO.
I still prefer to create those basic views as scenes in the SketchUp model. The scenes provide fixed points of reference for the model which you don’t get if you create the various views in LayOut.
You are not wrong, that is a fast easy way to get standard views. In fact, with the changes to Layout 2020 we can now chose any view we want, and any other view properties we want all from within Layout. I personally am migrating into a nearly scene-less workflow. But these are techniques for more experienced users to carefully employ, not for beginners.
For the OP, and anyone just learning how to work with Layout, understanding the relationship between scenes in SU and viewports in LO is a cornerstone of learning and an important first step.