Hey, I'm trying to calculate the distance between a point and a line segment with a function. The only possible line segments are in 45 degree rotations, eg: _ | / \
I almost have it done, but my last problem is that if the line is in this orientation / it seems to move the line or somehow thing that it is like \ This is what I have so far. THe code at the beginning prevents similar screw ups like this with the other line orientations bu just swaping the pairs of coordinates.
' Calculate the distance between the point and the segment
Public Function DistanceToLine(PX As Single, PY As Single, X1 As Single, Y1 As Single, X2 As Single, Y2 As Single) As Single
Dim TempX As Single, TempY As Single
Dim DX As Single, DY As Single
Dim T As Single
'Swap coords if needed to keep the first one smaller
If (X1 > X2) Or (Y1 > Y2) Then
TempX = X1
TempY = Y1
X1 = X2
Y1 = Y2
X2 = TempX
Y2 = TempY
End If
' Calculate the distance between the point and the segment
DX = Abs(X2 - X1)
DY = Abs(Y2 - Y1)
T = (PX + PY - X1 - Y1) / (DX + DY)
If T < 0 Then
DX = PX - X1
DY = PY - Y1
ElseIf T > 1 Then
DX = PX - X2
DY = PY - Y2
Else
X2 = X1 + T * DX
Y2 = Y1 + T * DY
DX = PX - X2
DY = PY - Y2
End If
DistanceToLine = Sqr(DX * DX + DY * DY)
End Function
Thanks, Jebus
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ok, i am sure i can do this i just need a bit more info, you want to measure the distance from a random point to a line that will always be in 45 degree increments?
This doesnt make much sense because there are an infinite number of points on a line so you have to pick a point to measure to on the line. unless you are trying to measure from a point to the center of line. So where exactly on the line are you measuring to?
The shortest distance between a point (x0,y0) and the line ax+by+c=0 is
|ax0 + by0 + c|/sqrt(a^2 + b^2)
Using that, this function should work:
Public Function DistanceToLine(PX As Single, PY As Single, X1 As Single, Y1 As Single, X2 As Single, Y2 As Single) As Single
Dim A As Single, B As Single, C As Single
A = Y1 - Y2
B = X2 - X1
C = X1 * Y2 - X2 * Y1
DistanceToLine = Abs(A * PX + B * PY + C) / (A ^ 2 + B ^ 2) ^ 0.5
End Function
Ok, I got it done, thanks so much here it is.
'Calculate the distanDistanceToLinece between the point and the segment
Public Function DistanceToLine(PX As Single, PY As Single, X1 As Single, Y1 As Single, X2 As Single, Y2 As Single, MaxHitDistance As Single) As Single
Dim A As Single, B As Single, C As Single, Distance As Single
A = Y1 - Y2
B = X2 - X1
C = X1 * Y2 - X2 * Y1
Distance = Abs(A * PX + B * PY + C) / (A ^ 2 + B ^ 2) ^ 0.5
'Crop the distance to fit the line segment and not an infinate line
'If the line is running left to right
If Distance < MaxHitDistance Then
If X1 < X2 Then
If PX < X1 Then
DistanceToLine = X1 - PX
ElseIf PX > X2 Then
DistanceToLine = PX - X2
Else
DistanceToLine = Distance
End If
'If the line is running right to left
ElseIf X1 > X2 Then
If PX > X1 Then
DistanceToLine = PX - X1
ElseIf PX < X2 Then
DistanceToLine = X2 - PX
Else
DistanceToLine = Distance
End If
'If the line is vertical
ElseIf X1 = X2 Then
'If the vertical line is top to bottom
If Y1 < Y2 Then
If PY < Y1 Then
DistanceToLine = Y1 - PY
ElseIf PY > Y2 Then
DistanceToLine = PY - Y2
Else
DistanceToLine = Distance
End If
'If the vertical line is bottom to top
ElseIf Y1 > Y2 Then
If PY > Y1 Then
DistanceToLine = PY - Y1
ElseIf PY < Y2 Then
DistanceToLine = Y2 - PY
Else
DistanceToLine = Distance
End If
End If
End If
Else
DistanceToLine = Distance
End If
End Function
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by: NBrownohPosted on 2003-11-14 at 22:38:24ID: 9753141
that little function below will measure the length of any line, is that what you are looking for?
Public Function DistanceToLine(X1 As Double, Y1 As Double, X2 As Double, Y2 As Double) As Double
Dim HLen As Double, WLen As Double, TRoot As Double
HLen = Abs(X1 - X2)
WLen = Abs(Y1 - Y2)
HLen = HLen * HLen
WLen = WLen * WLen
TRoot = Sqr(WLen + HLen)
DistanceToLine = TRoot
End Function