AP_Scripting: added example for orbit follow

allows a following vehicle to orbit the lead vehicle

libraries/AP_Scripting/examples/orbit_follow.lua

@@ -0,0 +1,44 @@
+-- example that does an orbit of a vehicle that is being followed
+-- by adjusting the follow offset X and Y parameters
+-- user settable FOLL_ORB_TIME and FOLL_ORB_RADIUS parameters
+-- are provided for the time for one orbit (in seconds) and the radius
+-- of the orbit
+
+-- setup param block for FOLL_ extensions
+local PARAM_TABLE_KEY = 83
+local PARAM_TABLE_PREFIX = "FOLL_"
+assert(param:add_table(PARAM_TABLE_KEY, PARAM_TABLE_PREFIX, 2), 'could not add param table')
+
+function bind_param(name)
+   local p = Parameter()
+   assert(p:init(name), string.format('could not find %s parameter', name))
+   return p
+end
+
+function bind_add_param(name, index, default_value)
+   assert(param:add_param(PARAM_TABLE_KEY, index,  name, default_value), string.format('could not add %s', PARAM_TABLE_PREFIX .. name))
+   return bind_param(PARAM_TABLE_PREFIX .. name)
+end
+
+local FOLL_OFS_X = bind_param("FOLL_OFS_X")
+local FOLL_OFS_Y = bind_param("FOLL_OFS_Y")
+local FOLL_ORB_RADIUS = bind_add_param("ORB_RADIUS", 1, 5)
+local FOLL_ORB_TIME = bind_add_param("ORB_TIME", 2, 10)
+
+local t = 0
+
+function update()
+   t = t + 0.1
+   --gcs:send_text(0, string.format("t=%.2f X=%.2f Y=%.2f", t, FOLL_OFS_X:get(), FOLL_OFS_Y:get()))
+   if t > FOLL_ORB_TIME:get() then
+      t = t - FOLL_ORB_TIME:get()
+   end
+   FOLL_OFS_X:set(math.cos((t/FOLL_ORB_TIME:get())*2*math.pi)*FOLL_ORB_RADIUS:get())
+   FOLL_OFS_Y:set(math.sin((t/FOLL_ORB_TIME:get())*2*math.pi)*FOLL_ORB_RADIUS:get())
+   return update, 100
+end
+
+gcs:send_text(0, string.format("orbit started"))
+return update, 100
+
+