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Cosmos75
06-28-2004, 11:37 AM
I am having some trouble getting code to work.

I have the x & y coordinates of locations and the elevations for the starting and ending coordinates. The assumption I have is that the elevation change from the first point to the last point is constant (i.e. changes equally over equal distance in a straight line).

But the coordinates I have are not in a straight line.

x, y, Elevation (ft)
0 0 0
2 2
5 2
3 9
10 10 100

The elevations should be
x, y, Elevation (ft)
0 0 0
2 2 20
5 2 35
3 9 60
10 10 100

e.g.
y = f (x) = 10x
- This is the equation for the line from the starting-ending points
To find the elevation for (5,2) I need to find the equation for a line perpendicular to my starting-ending line that intersects (5,2). All points along this line will have the same elevation (or any points along a line perpendicular to the starting-ending line for that matter).

An equation for a straight line takes the form of

y = Ax + C
where,
A = Slope of line
C = Constant (i.e. where line intersects y-axis when x = 0)

A line perpendicular to this will have this form
yp = -x/A + Cp
where,
yp = Perpendicular function
Cp = Constant (may or may not be equal to C)

Using the intersection point between these two lines and the equation for my starting-ending line, I can figure out the elevation for (5,2).

On top of that I have gaps between my data
x, y, Elevation (ft)
0, 0, 0
2, 2,
5, 2,
3, 9,
10, 10, 100
11, 12,
12, 15,
15, 16,
20, 20, 220

You may have noticed that (20,20) has an elevation of 220 not 200. In this case the starting point is (10,10) and the ending point is (20,20).
:wot
So I have created a function that uses UDT (User Defined Type) to calculate this for me.


Public Type udtXYFunction
xySlope As Double
xyConstant As Double
xyY As Double
xyX As Double
End Type

Sub funcLER()

Dim LastRow, StartRow, EndRow As Integer
Dim CurrentElevation, StartElevation, LastElevation, _
EndElevation, RatioElevation As Double
Dim coorX1, coorX2, coorY1, coorY2 As Double
Dim TotalDistance, RatioDistance As Double
Dim intersectX As Double
Dim Slope As Double
Dim Constant As Double
Dim SlopePerpendicular, ConstantPerpendicular, _
PerpendicularX, PerpendicularY As Double

'Find last row with data
LastRow = Cells(65536, 1).End(xlUp).Row

'Starting Elevation
StartElevation = Cells(1, 3).Value

'Ending Elevation
LastElevation = Cells(LastRow, 3).Value
StartRow = 1

For i = 2 To LastRow
CurrentElevation = Cells(i, 3).Value
If Cells(i, 3).Value <> 0 Then
EndElevation = CurrentElevation
EndRow = Cells(i, 3).Row
Cells(i, 3).Font.Bold = True
If EndRow - StartRow = 1 Then
StartRow = EndRow
StartElevation = EndElevation
Else
For h = StartRow + 1 To EndRow - 1

'Elevation Difference
ElevationDiff = EndElevation - StartElevation
'Total Length
TotalDistance = CalcDistance(Cells(StartRow, 1), Cells(i, 1), Cells(StartRow, 2), Cells(i, 2))
'Slope & Constant for Start-to-End function, i.e. y(x)
Slope = CalcXYFunction(Cells(StartRow, 1), Cells(EndRow, 1), Cells(StartRow, 2), Cells(EndRow, 2)).xySlope
Constant = CalcXYFunction(Cells(StartRow, 1), Cells(EndRow, 1), Cells(StartRow, 2), Cells(EndRow, 2)).xyConstant

'Slope for a perpendicular line, i.e. y2(x)
SlopePerpendicular = -1 / Slope
ConstantPerpendiclar = Cells(h, 2) + (SlopePerpendicular * Cells(h, 1))

'Find intersection point
intersectX = (ConstantPerpendicular - Constant) / (Slope + SlopePerpendicular)
intersectY = XYFunction(0, intersectX, Slope, Constant).xyY

Next h

StartRow = EndRow
StartElevation = EndElevation
End If
End If
Next i

End Sub

Function CalcDistance(X1 As Double, X2 As Double, Y1 As Double, Y2 As Double) As Double

Dim B, C As Double

B = (X1 - X2) ^ 2
C = (Y1 - Y2) ^ 2

CalcDistance = Sqr(B + C)

End Function

Function CalcXYFunction(X1 As Double, X2 As Double, Y1 As Double, Y2 As Double) As udtXYFunction

CalcXYFunction.xySlope = (Y2 - Y1) / (X2 - X1)
CalcXYFunction.xyConstant = Y1 - (CalcXYFunction.xySlope * X1)

End Function

Function XYFunction(Y As Double, X As Double, Slope As Double, Constant As Double) As udtXYFunction
XYFunction.xyY = (Slope * X) + Constant
XYFunction.xyX = (Y - Constant) / Slope

End Function
I keep running into a problem using the function XYFunction when the function inputs are calculated using other functions.

When I do Dim interceptY as Double, I get this error.

?Compile Error:

ByRef argument type mismatch?
:confused:
When I don?t Dim interceptY as Double, I get this error.

?Compile Error:

Only user-defined types defined in public object modules can be coerced to or from a variant or passed to late-bound functions.?
:bawl

The line that is causing me problems is bolded in red.

What am I doing wrong? I am using Excel 2000.
:help

Thank you in advance to anyone who even bothers to read through all of this!
:)

TonyJollans
06-28-2004, 11:48 AM
Have you tried ..

Dim intersectY As udtXYFunction

.. so that it doesn't have to coerce a variant to your UDT. I haven't tried it, but it should work.

Cosmos75
06-28-2004, 07:54 PM
Tony,

Thanks for your reply! I really appreciate it!
:)

Will let you know if that works.

Found some mathematical mistakes in my code that I need to correct.
:eek:

To be honest, I have no idea what "coerce a variant to your UDT" means!
:confused:

I've used UDT before in Access with no problems, though.

Zack Barresse
07-08-2004, 10:34 AM
Hey Cosmos, how'd it turn out?