Modeling a Complex Structure - Google SketchUp Workshop: Modeling, Visualizing, and Illustrating - page 209

Tip
In this stage - and especially in stage 4 - orthogonal views need to be used
to align the paths with the plan and the section. Two scenes should be
created, one for the plan and one for the section, and perspective should
be turned of for both of them (from the Menu Bar, choose Camera >
Perspective [unticked]). To make sure that there is a square-on view of these
working planes, enter the working plane group, select one of the surfaces,
right-click, and choose Align View from the contextual menu. These two
scenes will be used often in this project.
Stage 4: The Construction of the Path of the
First Girder on Elevation
Objective : To construct the “scaffolding” for the profile of the first girder.
Data : Model obtained in the previous stage.
Tool : SketchUp Pro.
The first step is to reduce the opacity of the working plane surface, so that
the section can be seen behind it. Then, starting on either the left- or the
right-hand edge of the surface, the path of the girder is traced using
the Line tool, making sure that the line drawn adheres to the surface
(SketchUp's inferencing engine should do this automatically: Look out for
the On Surface tooltip). The working plane surface can now be deleted or
hidden; only the line is needed for the next stages. Use the Orbit tool here
to verify that the line follows the path of the girder both on plan and on
elevation (see Fig. 12.4).
FiG 12.4 Construction of the profile on the surface of the working plane: Final profile, showing the crank in two planes.