Graphing in point perspective:
This
was a quick experiment in point projection done before I drew
the leaning tower of Pisa, 2003. It was based off an old
2D version I graphed (2001) when I first learnt about mathematical functions (below,
Equations for 2D graph)
Imagine that the bridge is like a long door on hinges. The door post
is “H” units to the left of the viewer and “L” units in front of him/her.
“A” is how far (rad or degrees) the door has spun around. “t” is the
length along the door.
The scene is projected onto a plane that is 1 unit away from the viewer (to
make things easy and scale is only effected anyway).
I used 6 for H and L. a good value for “A” is anywhere between 90 and 20 degrees.
The general equation can be found quickly using similar
triangles. it is:
x=(right-left distance)/(forward distance)=(-H+t*cos(A))/(L+t*sin(A))
y=(vertical height)/(forward distance)=f(t)/(L+t*sin(A))
in this case, f(t)={a line, or a circle}
A line in the above graph:
X1=(-H+t*cos(A))/(L+t*sin(A))
Y1=3/(L+t*sin(A))
An arch in the above graph:
X3=(-H+t*cos(A))/(L+t*sin(A))
Y3=(sqrt(3^2-(t-3)^2)-1)/(L+t*sin(A))

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