# Understanding rho and theta in hough

I understood the concept behind Hough transform. One thing i am still unsure is the rho and theta range of hough transform. The range is given below.

If theta is in the range [0,pi), then rho values can have negative values. If theta is in the range[0,2pi), then rho can have only positive values.

How can rho be negative ?. Is the range standard for all the images ?. I have referred questions on Hough Transform under stack overflow as well as dsp-stackoverflow, but it wasn't helpful. Can someone explain me bit more clearly please ?.

• a positive distance and an angle in $$[0,\,2\pi[$$
• a signed distance and an angle in $$[0,\,\pi[$$