Visual field analysis with isovist component issue

Hi. I have been trying to use ISOVIST component to achieve the visual field analysis. This is attempt to understand where the most publicly orientated spots within path network in simple path and plot boundary situation. I think it is kind of working with line connection but when I tried to visualize this visual field with mesh color viewer as it was suggested by David. (  http://www.grasshopper3d.com/forum/topics/sightlines-problem?commen... )

However, the result that I got at the moment is just minor color variation and not much differentiation. I tried to increased the number of vertexes from mesh grid but the result is more or less same. Can anyone suggest better way or point out what the problem is?

Thanks.

Regards,