I use an adaptation of the Daniel Greene method referenced by Steven in the prior thread (
http://forum.portraitartist.com/show...?threadid=1543 ), which includes presumptions about regularly placed features. I mention that this is
only relevant when painting a head straight on; when an extreme angle is involved, you need to use a simple "unit of measurement" approach.
I think of my approach as the halfway approach; rather than dividing space in thirds, I use halves...it's easier for me to find halfway point on the model, and easier to find them on my canvas.
In an adult head the eyes, that is the caruncles (or as Harley Brown says "The pink things!"), are vertically right in the middle of the skull (not the top of the hair). There is virtually no variability in this measurement in a normal adult head. Determine the height of the head you will paint, and place a mark halfway. Verify this persumption with the straight-armed, one-eyed method described by Michele here:
http://forum.portraitartist.com/show...&threadid=1531
In most adults, the next halfway point between the caruncle and the chin falls vertically between the base of the nose's wing, and the top of the upper lip. Mark this halfway point, too. From here I proceed to judge how much above the halfway mark the nose begins, and how much below the half way mark the upper lip begins. I meausre, lightly mark, and measure again (or as many times as necessary to feel that the placement is accurate. Only then do I go on to the next measurement.
From this point I have begun to establish a series of accurately placed landmarks, and I then measure distance on the model, not presumed distances, and compare them to what I have already placed on the canvas, verifying and placing as I go.
I agree with Mr. Greene, it's easier to place the vertical measurements first, then deal with horizontal relationships.
Once you move beyond the intial eye placement, there is quite a bit of variation in human faces. No, not all eyes are one eye-width apart! You have to measure the
individual in front of you to decide. There is a lot of variability in nose width, eyebrow width, mouth width, chin length, and mid-face length.