Revilations

[TJ_Tigger]

Well at least to me. I was working on a function to calculate the distance between two waypoints(defined by longitude and latitude) and in working in building a function found a couple of things.

1. LUA has a math.pi function built into it to define the value of pi.

2. don't try to declare a variable as a local variable twice in the same block. LUA doesn't like it. I ended up with a function where I included an if statement to figure out if the difference between two longitude measurements was greater or less than 0 and had two local declarations one in the true and false for the same variable. AMS/LUA doesn't like it. Stay away from it

Just thought I would share. Here is the function that figures distance and angle between two points on a geodisic sphere.

-- returns two values, one the distance betwen the two points and the angle between the two.
-- latitude and longitude need to be defined as radians not degrees.
function DistAngle(nlat1, nlon1, nlat2, nlon2)
	local distance = 2 * Math.Asin(Math.Sqrt((Math.Sin((nlat1 - nlat2)/2))^2 + Math.Cos(nlat1)*Math.Cos(nlat2)*(Math.Sin((nlon1 -nlon2)/2))^2));
	if Math.Sin(nlon2 - nlon1) < 0 then
		angle = Math.Acos((Math.Sin(nlat2)-Math.Sin(nlat1) * Math.Cos(distance))/(Math.Sin(distance)*Math.Cos(nlat1)));
	else
		angle = 2 * pi - Math.Acos((Math.Sin(nlat2) - Math.Sin(nlat1) * Math.Cos(distance))/(Math.Sin(distance)* Math.Cos(nlat1)))
	end	
	return distance *180*60/pi, Math.Deg(angle)
end

Tigg

BTW don't ask me about the math because I found the calulations on the web . . . somewhere.

[Corey]

Cool post!

Corey Milner
Creative Director, Indigo Rose Software

[Bruce]

He did this during lunch breaks no less!

[TJ_Tigger]

Thanks. BTW this is what AMS did not like. Debug is a good thing

function DistAngle(nlat1, nlon1, nlat2, nlon2)
	local distance = 2 * Math.Asin(Math.Sqrt((Math.Sin((nlat1 - nlat2)/2))^2 + Math.Cos(nlat1)*Math.Cos(nlat2)*(Math.Sin((nlon1 -nlon2)/2))^2));
	if Math.Sin(nlon2 - nlon1) < 0 then
		local angle = Math.Acos((Math.Sin(nlat2)-Math.Sin(nlat1) * Math.Cos(distance))/(Math.Sin(distance)*Math.Cos(nlat1)));
	else
		local angle = 2 * pi - Math.Acos((Math.Sin(nlat2) - Math.Sin(nlat1) * Math.Cos(distance))/(Math.Sin(distance)* Math.Cos(nlat1)))
	end	
	return distance *180*60/pi, Math.Deg(angle)
end

[Corey]

He did this during lunch breaks no less!

I can easily picture Tigg carving the model for this function in his mashed potatoes like Dreyfuss in Close Encounters.

I wonder if this calculation is technically considered to be bipolar?

Corey Milner
Creative Director, Indigo Rose Software