Equation of the line, vertical I need to find the equation of the line, so I want to use y-y1=m(x-x1)  but for a vertical line the slope is undefined.  So I am unsure how to proceed.
A vertical line in the plane is defined by the equation $x = c$, where $c$ is some real. This makes sense because along the vertical line, the $x$ value doesn't change.
How about below parameterization.

$ \rho = x \cos{\theta} + y \sin{\theta}$ 

where 

$ \rho $ = perpendicular distance to the line from the origin (0,0)

$ \theta $ = angle of a line perpendicular to our line with the x axis

you can take a look at http://en.wikipedia.org/wiki/Hough_transform.

when line slope is $90^o$, $\theta = 0^o$, then $ \rho = x $.