Are you talking about the web based app or the iPad version?
I have the iPad version handy right now. You need to first select the gray mountain icon on the right hand side (third one down from the top). This enables the geodetic mode.
You can now plant two flags, a red one and a gray one, on the map. The app will tell you the distance from the red to the gray flag, the elevation change and the max altitude degree. This information coupled with the position of the sun or the moon should help you decide if your view will be blocked.