A while ago, quite a while ago, I started a linear perspective instructional work for artists. Progress faltered as the difficulty in explaining a rather simple subject struck home. Yes that right, simple, because that's the truth, there are however certain details that need to be grasped with adequate understanding for any instruction to be useful. This together with the fact that my attention began to wander from the purpose of instruction as I became distracted by the details and implications of the subject, meant that the results where far from satisfactory.
So, I sort of gave up on the topic but recently I've come across a few examples of instruction on the subject that were so bad, that I decided I just had to grasp the nettle. So the following is a very basic explanation of the linear perspective technique for constructing drawings.
The square at the bottom and to the left of the drawing represent views of the subject, a cube. The bottom one is the view from the top (plan view), the one on the left, the view from the side.
The points where the radiating lines converge, also at the bottom and the left, represent the view origin and the pink lines the view direction. Where those pink lines intersect is the centre of the view, analogous to the location a viewer would be looking.
Those grey lines, or rays if you like, plot the location of various points on for each view and project them onto a plane, represented by the green lines. Those points where the rays intersect the plane, are then extended onto the drawing. Where an extended line intersects with a corresponding line, ie one that is plotted from the same point on the corresponding view, is the location of that point projected into linear perspective.
Voila he said in faux froggese, linear perspective in one easy step. As simple as this example is, that's really all you need to know. Of course that's not really very satisfactory because for useful instruction, certain implications need to be spelled out explicitly. For instance where are the vanishing points and the terminator lines? Do I really have to draw everything out in plan and side view to construct a perspective drawing?
Fear not for there's a reasonable chance that the answer to those questions will be appearing soon, if I get round to writing the next instalment that is.