Clockwise from top left: ViewCatcher, Hor:ratio, mirror compass, bubble level, drafting compass, line level, reticuLanyard.
The ViewCatcher is a handy tool for framing a view out of a scene. It has presets for commonly used aspect ratios like 8" X 10",9" X 12" etc.
I sometimes use it in conjunction with Hor:ratio to set it to specific proportions or to search for interesting proportional relationships in a framing determined by the subject matter.
The mirror compass can be useful to predict changes in the direction of the sunlight, or to find your way home, for that matter, but its main purpose here is when combined with the bubble level:
The idea is to be able to be able to find your own eye level and relate it to a point or points in the scene. Use the mirror to view the bubble level, and raise the whole contraption until the bottom of the compass base appears as a flat line, neither above nor below your central line of sight.
Here it is at the scene of the truss bridge.
Juggling the compass and bubble level while looking into the distance takes some getting used to, but it's definitely doable. Jugging the device and a camera to take a picture at the moment it all aligns was really a challenge. I didn't quite get it to flat line from the camera's point of view, but I hope you get the concept. When my eye was actually level with the device, the horizon line was located right about where the central pier of the distant bridge starts to curve into the archway.
I find myself consistently surprised at how high my actual line of sight is when parallel to the ground. I must slouch around with downcast eyes a lot.
Here you can see the horizon drawn in, along with square reference box, principal vanishing point and diagonal vanishing point lines, as seen in Perspective Hacks. The heavier dots up and down the vertical line are measuring points taken with the drafting compass, used as a divider or caliper to measure lengths and distances. I use both the drafting compass and the line level as accessories to the ReticuLanyard, which is a made up name for the plastic ruler with an adjustable strap at the bottom of the photo. I threw it together based on this post by Rebecca, who also suggested the addition of a level.
The notation at the bottom, 45:15, is the relationship between the sight size of my "basic unit," for which I used the distance from the principal vanishing point to the bottom of the picture, and the drawn size of the same unit. I wrote it that way instead of simply 3:1 because I used the 60th scale on Hor:ratio to be able to easily multiply or subdivide observed measurements.
The combination of all of these devices and techniques really changes the way it feels to stand in an environment and try to come to grips with how to draw it. I don't think it's always appropriate to work this way; I still like to simply plunge in and see what happens when I eyeball it, but I think it's a good experience to calibrate your perceptual relationship to the space around you this way.
As with my other experiments with the dresser and climbing structure, I found that doing these careful measurements of the truss bridge revealed just what a rickety, out of true and fundamentally non-Euclidean structure it is. I'll think twice about riding my bike over it now.