From Q let fall the vertical line Q P′.
Join P T, cutting Q P in P′.
P′ is the point required.
If the point P is above the eye of the observer instead of below it, C P is to be measured upwards from C, and Q P′ drawn upwards from Q. The construction will be as in [Fig. 5.]
Fig. 5.
And if the point P is to the right instead of the left of the [p12] ]observer, D C is to be measured to the right instead of the left.
The figures [4.] and [5.], looked at in a mirror, will show the construction of each, on that supposition.
Now read very carefully the examples and notes to this problem in Appendix I. ([page 69]). I have put them in the Appendix in order to keep the sequence of following problems more clearly traceable here in the text; but you must read the first Appendix before going on.
[Footnote 8: ] More accurately, “To fix on the plane of the picture the apparent position of a point given in actual position.” In the headings of all the following problems the words “on the plane of the picture” are to be understood after the words “to draw.” The plane of the picture means a surface extended indefinitely in the direction of the picture.] [Return to text]