Range Of Vision
How big a 'cone of vision' circle to draw within? -From the center of vision point ('CV') upon the horizon to the furthest corner of your drawing times two
equals the diameter of the Range Of Vision circle, the 'ROV'.X-CV
ROV times .866 is the [X-CV] distance from CV straight up to the 'X' point (the camera, or your eyes). From X, one can use a protractor and a long ruler to locate vanishing points upon the horizon, but that is not completely precise, nor entirely convenient. With this utility (click the page's link above), the resultant number is (in inches) that degree's vanishing point's horizontal distance from CV.
In the future I plan to remake this
to output a whole range of incremented degrees
for a given ROV.
...Win7 precludes me from running my old DOS utility, XCV#4.EXE