SSub get_angle(x1, y1, x2, y2, angl)
    pai = 3.14159265358979
    xx = x2 - x1: yy = y2 - y1
    If yy = 0 Then
        If 0 < xx Then angl = 0
        If xx < 0 Then angl = pai
        GoTo endline
    End If
    If xx = 0 Then
        If 0 < yy Then angl = pai / 2
        If yy < 0 Then angl = -pai / 2
        GoTo endline
    End If
    angl = Atn(yy / xx)
    If xx < 0 Then angl = angl + pai
endline:
End Sub