Sun Sep 29 11:32:04 PDT 1996

OK, let's see if I can remember (or rederive) my algebra.

The latitude seems to have a common origin, zero degrees = 0 northing.
But longitude seems to have a 180-degree opposite origin.

If we have two points, how do I find the slope and intercept?

For this example,
point 1 is   460419.53, -87.5, and
point 2 is   480295.83, -87.25.

This is simple algebra, isn't it? No, it's two simultaneous equations.

y1=m(x1)+b
y2=m(x2)+b

y1-y2 = m(x1-x2)
(y1-y2) / (x1-x2) = m.  OK, that looks right.  Now substitute.

y1 = ((y1-y2)/(x1-x2))(x1) + b    Thus
y1 - ((y1-y2)/(x1-x2))(x1) = b.  Or

y1 - m(x1) = b, or
y2 - m(x2) = b.