I often start a sketch in the wild by using sight sizing directly on the page to do the initial layout. I hold up the sketchbook to the scene and make little tick marks at the top and side to mark the coordinates of the big shapes and salient landmarks, then map them onto the the page.
Accuracy depends on keeping the distance between the eye and the drawing surface constant, and keeping the vertical and horizontal orientation plumb and level. I usually do this by the seat of my pants, but the complexity of that Mr. Cone sketch made me want to add some controls.
This is what I came up with - a backing to mount the sketchbook on, made out of three small hardboard pieces Velcroed together.
It can broken down and carried easily.
It is attached an adjustable strap around my neck.
PlumBobby is a simple inclinometer made of two bobby pins suspended from a binder clip and straddling a paper clip. If the sketchbook tilts out of the vertical plane, one of the bobby pins will rattle against the paper clip to alert me.
A sketch I started to test it out, and the same sketch cleaned up a bit. I wanted to get the proportions of the shed as well as its relationship to the little birdhouse on the left.
This photo has more pronounced linear perspective than the sketch. I think that the mindset of mapping things onto the picture plane caused me to overlook the perspective, so that's just something to keep in mind.
I didn't even consider this when doing the original design, but it turns out to be easy to change to portrait orientation by simply rotating the middle panel 90˚ and adding a couple binder clips.
A quick test sketching a maple tree and front and back view of the whole assembly.
