AP_Scripting: added qnh_alt example

useful for BVLOS ops

Author: tridge

libraries/AP_Scripting/examples/qnh_alt.lua

@@ -0,0 +1,51 @@
+--[[
+    example that sends QNH altitude to GCS as a NAMED_VALUE_FLOAT QNG_ALT_FT in feet
+
+    Note: operator must be QNH_PRESSURE in hPa before each flight!
+--]]
+
+local MAV_SEVERITY = {EMERGENCY=0, ALERT=1, CRITICAL=2, ERROR=3, WARNING=4, NOTICE=5, INFO=6, DEBUG=7}
+
+local PARAM_TABLE_KEY = 93
+local PARAM_TABLE_PREFIX = "QNH_"
+
+-- add a parameter and bind it to a variable
+function bind_add_param(name, idx, default_value)
+   assert(param:add_param(PARAM_TABLE_KEY, idx, name, default_value), string.format('could not add param %s', name))
+   return Parameter(PARAM_TABLE_PREFIX .. name)
+end
+
+-- setup script specific parameters
+assert(param:add_table(PARAM_TABLE_KEY, PARAM_TABLE_PREFIX, 8), 'could not add param table')
+
+--[[
+  // @Param: QNH_PRESSURE
+  // @DisplayName: QNH pressure in hPa
+  // @Description: QNH pressure in hPa
+  // @Range: 900 1200
+  // @Units: hPa
+  // @User: Standard
+--]]
+local QNH_PRESSURE = bind_add_param('PRESSURE', 1, 0)
+
+--[[
+    send QNH based alt to GCS
+--]]
+local function send_qnh_alt()
+    local pressure_Pa = baro:get_pressure()
+    local qnh_Pa = QNH_PRESSURE:get()*100
+    local alt_m = baro:get_altitude_difference(qnh_Pa, pressure_Pa)
+    local alt_feet = alt_m * 3.280839895013123
+    gcs:send_named_float("QNH_ALT_FT", alt_feet)
+end
+
+function update()
+    if QNH_PRESSURE:get() > 0 then
+        send_qnh_alt()
+    end
+    return update,1000
+end
+
+gcs:send_text(MAV_SEVERITY.INFO, "Loaded qnh_alt")
+
+return update,1000