A radar that reads exit velocity — a Pocket Radar or anything similar. That single number is all the app requires. Pitch speed is optional and only used to estimate your bat speed.
Elevation comes from GPS, which is typically accurate to somewhere between 30 and 100 feet vertically. That is close enough that the distance barely moves, but you can type in an exact number on the conditions screen and the app will use yours instead.
A radar gun cannot measure launch angle. If you do not enter one, the app simulates your swing at the angle that would carry farthest and tells you so, and shows you the distance at every other angle as well.
Measuring spin needs a spin-tracking unit, not a radar. The app uses a typical backspin for the launch angle you hit, and labels that number "assumed" so you always know which figures are measured and which are estimated.
Weather needs a network connection. Without one the app falls back to neutral conditions and lets you type in the temperature and wind yourself — nothing breaks.