How to get bearing from one unit to another?

[Bearfoot]

Given two units, I would like to get the bearing of unit from another.

 

I have got the following code:

 

function calcBearing(dx, dz)
   -- dx = to_x - from_x -- where x corresponds to first horizontal coordinate
   -- dz = to_z - from_z -- where z corresponds to second horizontal coordiante
   local bearing = nil
   if dx ~= 0 then
       -- local angle = (math.atan(dz, dx) * 180/math.pi)
       local angle = math.atan(dz, dx)
       bearing = angle
   elseif dz > 0 then
       bearing = 0
   elseif dz < 0 then
       bearing = 180
   else
       bearing = 0
   end
   if bearing < 0 then
       bearing = bearing + 360
   end
   bearing = bearing % 360
   return bearing
end

unit1 = Unit.getByName("Pilot #001")
unit2 = Unit.getByName("Pilot #002")
pos1 = unit1.getPosition().p
pos2 = unit2.getPosition().p
dx = unit2.x - unit1.x
dz = unit2.z - unit1.z
bearing = calcBearing(dx, dz)
trigger.action.outText("Bearing of unit 2 from unit 1: " .. bearing, 1)

 

And it works in the sense that it produces a result between 0 and 360, but the numbers do not make sense. I think either the origin of the coordinate system or the fact that I am not taking into account heading is the problem?

 

What am I doing wrong? Is there a better way to go around this?

[FSFIan]

The trigonometric functions in Lua, like in most other programming languages, use radians instead of degrees to express angles.

 

A full circle is 2*pi.

 

function deg2rad(deg)
   return deg/180*math.pi
end
function rad2deg(rad)
   return rad/math.pi*180
end

[Bearfoot]

Ian;2771959']The trigonometric functions in Lua' date=' like in most other programming languages, use radians instead of degrees to express angles.

 

A full circle is 2*pi.

 

function deg2rad(deg)
   return deg/180*math.pi
end
function rad2deg(rad)
   return rad/math.pi*180
end

 

Ah yes. In the production version, I actually do this conversion (you can see it commented out above). I was just experimenting to see if the radians/degrees things was the issue.

 

But even with the conversion, it does not always makes sense.

 

E.g. given a 4-ship right-heavy wedge heading (roughly) north,

 

   
   1
2       3
           4

 

The bearing from 3 to 4 as reported by the above is 88.85, i.e. ~90 after accounting for error.

 

Heading roughly east is ~270.

 

Heading roughly south is also ~270.

 

Heading roughly west is also ~90.

 

So, first of all, the bearing from 3 to 4 should be invariant (IMHO) with respect to heading.

Secondly, I cannot see how any of those bearings make sense from what I see on the map of the relative positions of 3 and 4.

I would expect ~135, regardless of heading.

[Bearfoot]

Update.

 

Fixed how the angles are normalized, and now I think I am getting correct absolute bearings (with 0 deg = North):

 

function calcBearing(dx, dz)
   -- dx = to_x - from_x -- where x corresponds to first horizontal coordinate
   -- dz = to_z - from_z -- where z corresponds to second horizontal coordiante
   local bearing = nil
   if dx ~= 0 then
       local angle = math.atan2(dz, dx)
       if angle < 0 then
           angle = angle + 2 * math.pi
       end
       bearing = math.deg(angle)
   elseif dz > 0 then
       bearing = 0
   elseif dz < 0 then
       bearing = 180
   else
       bearing = 0
   end
   return bearing
end

 

Of course, what I want is relative bearings ...

[Bearfoot]

Ok, figured it out:

 

local unit1_velocity = unit1_unit:getVelocity()
local unit1_heading = calcFormationUnitBearing(unit1_velocity.x, unit1_velocity.z)
local relative_bearing = (360 - unit1_heading + absolute_bearing) % 360

 

where 'absolute_bearing' is given by the 'calcBearing()' function above