Observations of Sketched Trusses, Pt. 1

The most recent screencasts of sketched data contained examples from three sample truss structures. The sample truss structrues consisted of the following:

• 1-layer truss with 2-triangle width
• 1-layer truss with 3-triangle width
• 2-layer truss with 2-triangle width

Based on the collected screencasts of the most recent study, here are some observations.

1) Trusses are not built directly from triangles.

• Triangles in isolation are three lines uniquely connected at their endpoints.  When pointed upward, the triangle forms part of supports in civil and mechanical engineering.
• For sketched trusses though, the collected data do not show any instance of triangles being drawn.  Instead, shapes of triangles are drawn indirectly as part of the larger truss structure.
• Specifically, triangular shapes are formed where at least one line in the triangular shape is not connected with an endpoint from the other two lines.  Stated another way, a non-endpoint of at least one line is coincident with the endpoint of one of the other two lines in the triangular shape.

2) Initially building trusses from a trapezoid is common.

• In sketching trusses, there is a common preference for starting the sketch of trusses by starting with the outer trapezoid shape.  This behavior isn't uniformly shared, but there is a large consensus for it.
• This behavior is more readily apparent for multi-layer trusses, where users probably start off with the trapezoid shape as a reference for sketching the rest of the truss structure.

3) Sloped lines within a truss that cross multiple layers are common.

• Within the outer trapezoid shape of multi-layer trusses exists two kinds of lines:
• horizontal lines
• sloped lines
• While horizontal lines serve as the border between these layers, sloped lines are visually filler that serve as lines that are parallel to the non-parallel-sides of the outer trapezoid shape.
• In order to decrease the number of directional changes of sketching, many of the users often draw sloped lines that cross multiple layers. This behavior is apparent for 2-layers, but it remains to be seen if this behavior persists for higher number of layers.