reorganize viewshed assignment

[petrasovaa]

• re-design the viewshed with the new Raleigh lidar data - include trees and buildings
• add r.cva - cummulative viewshed from multiple points (in G7 r.viewshed.cva)

[hmitaso]

I tried that using the 2015 dem and dsm at 1m resolution that we have for CC and did a view between JH topfloor/roof and Hunt lib terrace where I could go and verify the visibility. The results were non-trivial but maybe could be used to have the students think about what they are getting. Moving the coordinates on Hunt lib more towards the edge of terrace would probably help

r.viewshed dsm_2015 out=Huntview_dsm15 coord=638824.,223992. max_dist=10000 r.viewshed dem_2015 out=Huntview_dem15_1m coord=638824.,223992. max_dist=10000 observer_elevation=20 r.viewshed dsm_2015 out=JH2view_dsm15 coord=638913.,225412. max_dist=10000 r.viewshed dem_2015 out=JH2view_dem15_1m coord=638913.,225412. max_dist=10000 observer_elevation=22 r.viewshed elevation out=hunt_view coord=638824.,223992. max_dist=10000 observer_elevation=20 r.viewshed elevation out=jh_view coord=638913.,225412. max_dist=10000 observer_elevation=22