This is a little slide shows a line drawing of a pear and an apple tree in several subsequent steps. The first image is a grey scale photograph edited in photoshop elements to make zones in different tonalities visible. On site one can simulate this effect by squinting. After drawing the outline I continued to describe the foliage more detailed and tried to represent different tonalities with a more or less dense grid of lines. I tried to follow the pattern I saw in the foliage with the gel pen and represented the leaves on the outline of the tree top as little dots. On this occasion I noticed again how much information and insight on a subject is lost in a photograph.
Taking measurements is not a shame :). It helps a lot to train the hand and eye co-ordination for proper proportion estimates.