ardupilot/libraries/AP_Scripting/applets/mount-poi.md

# Mount POI

This script displays the location (lat, lon and altitude) that the gimbal is currently pointing towards

# Parameters

POI_DIST_MAX : POI's max distance (in meters) from the vehicle

# How To Use

1. Set RCx_OPTION to 300 or 301 to enable triggering the POI calculation from an auxiliary switch.  If 301 is used the gimbal will also lock onto the location
2. Optionally set POI_DIST_MAX to the maximum distance (in meters) that the POI point could be from the vehicle
3. Fly the vehicle and point the camera gimbal at a point on the ground
4. Raise one of the RC auxiliary switches and check the GCS's messages tab for the latitude, longitude and alt (above sea-level)

# How It Works

The script's algorithm is implemented as follows

1. Get the POI_DIST_MAX and TERRAIN_SPACING parameter values
2. Get the vehicle Location (lat, lon, height above sea-level), initialise test-loc and prev-test-loc
3. Get the vehicle's current alt-above-terrain
4. Get gimbal attitude (only pitch and yaw are used)
5. The test_loc variable is initialised to the vehicle's current location
6. The prev_test_loc variable is a backup of test_loc
7. test_loc is moved along the line defined by the gimbal's pitch and yaw by TERRAIN_SPACING (meters)
8. Get the terrain's altitude (above sea-level) at test_loc
9. Steps 6, 7 and 8 are repeated until test_loc's altitude falls below the terrain altitude
10. Interpolate between test_loc and prev_test_loc to find the lat, lon, alt (above sea-level) where alt-above-terrain is zero
11. Display the POI to the user