working out an angle from XY

[T0MMY]

For some game i'm creating, im trying to work out the angle the object is moving towards. Using the current X and Y and the old X an Y values, how could i get this?

thanks

[Jim Brown]

angle = arctan (deltaY/deltaX)

where the deltas are the change in x & y.

(At least, if I understand the question correctly)

[opus]

.. but don't forget to cover for situation when deltax=0 !

I know, I'm smartassing....
but I had to work around such a thing just yesterday, the error was clearly found, but nothing could be done to the executable. So I had to make sure the situation didn't occur from the user side. Two hours of work, just because those authors were so st....!

[alkatran]

Here is the function I use, I wrote in QB and it can probably be done better.

FUNCTION Target (SourceX, SourceY, DestX, DestY)
DIM Vertical AS SINGLE
DIM Horizontal AS SINGLE
DIM Diagonal AS SINGLE
DIM Vector AS SINGLE
Horizontal = ABS(SourceX - DestX)
Vertical = ABS(SourceY - DestY)
IF Horizontal AND Vertical <> 0 THEN
 Diagonal = SQR((Horizontal ^ 2) + (Vertical ^ 2))
 Vector = (Arcsin(Vertical / Diagonal))
 IF DestX > SourceX AND DestY > SourceY THEN Vector = 0 - Vector: Vector = Vector + 90
 IF DestX > SourceX AND DestY < SourceY THEN Vector = Vector + 90
 IF DestX < SourceX AND DestY > SourceY THEN Vector = Vector + 270
 IF DestX < SourceX AND DestY < SourceY THEN Vector = 180 - Vector: Vector = Vector + 90
ELSE
 IF Horizontal = 0 AND DestY > SourceY THEN Vector = 0
 IF Horizontal = 0 AND DestY < SourceY THEN Vector = 180
 IF Vertical = 0 AND DestX > SourceX THEN Vector = 90
 IF Vertical = 0 AND DestX < SourceX THEN Vector = 270
 IF Vertical = 0 AND Horizontal = 0 THEN Vector = 0: Target = 0: EXIT FUNCTION
END IF
DO UNTIL Vector <= 360 AND Vector > 0
 IF Vector <= 0 THEN Vector = Vector + 360
 IF Vector > 360 THEN Vector = Vector - 360
LOOP
Target = Vector
END FUNCTION

[opus]

Izt won't work since any Trig formula in VB will use/give radians NOT degrees!
Also keep in mind not everybody uses angels from 0 to 359, with 0 is North and 90 is East.
some are using a 0 that goes to the East and count than towards North !!
Believe me, I have to work with some of them, WEIRD!!!
I'm using this:

Public Sub Bearing(X1, Y1, X2, Y2, Bearing)
'Input X1, Y1, X2, Y2
'Output Bearing (0-360)
'Calculates Bearing from X1,Y1 to X2,Y2 using 360 degree-system
Const PI = 3.141592654
Dim dx As Single
Dim dy As Single
dx = X2 - X1
dy = Y2 - Y1
If dy <> 0 Then
        bearing = (Atn(dx / dy) * 180 / PI)
        If X2 > X1 Then
                If Y2 > Y1 Then
                        bearing = bearing
                Else
                       bearing = 180 +bearing
                End If
        Else
                If Y2 > Y1 Then
                        bearing = 360 + bearing
                Else
                        bearing = 180 + bearing
                End If
        End If
Else
        If X1 > X2 Then
                bearing = 270
        Else
                bearing = 90
        End If
End If
End Sub

[alkatran]

Actually I put Rad() and Deg() functions in all my programs, using them everytime I call a sin/cos.. although I suppose it would make more sense to only call once

[opus]

You are using

Vector = (Arcsin(Vertical / Diagonal))
IF DestX > SourceX AND DestY > SourceY THEN Vector = 0 - Vector: Vector = Vector + 90

So Vector is in radiants, and the following line uses Vector as it would be in Degrees!!!!

[alkatran]

My arcsin function (since Basics don't include them ) has the deg() built into it.

[opus]

Good idea, and yes I did miss the point that you were using a not built-in Function (ARCSIN).
Shouldn't you have been telling that?
Note:
After doing the testing on a simulation software for three years now, I've probably seen all kinds of false angle display's because of a mixed use of degrees and radians.
I hate those.........