cscommands.commat_show_distance_field
0=Off, 1=Visualize trace from camera, 2=Visualize occlusion, 3=Visualize far field trace from camera
For this command to work you must first run
sv_cheats true in the console. It only works on a local map or a private server — not in matchmaking. sv_cheats is a built-in Valve command and is completely safe from VAC.