Hi Isaac,
you can put this statement in your code:
'~~~~~~~~~~~~~~~
Stop
'~~~~~~~~~~~~~~~
then press F8 to step through the code one line at a time.
press CTRL-G to turn on the Immediate window. to find out a value of a variable, type this:
? MyVariablename
and press ENTER
when you want to execute the next line of code, if you are in the Immediate window, click on the titlebar for the code windows and press F8
as you probably realize, we can't travel as the crow flies so calculating ditance from coordinates won't really be how far you have to go ;)
If you do not figure out the problem, Please post the code that is doing the calculations
Warm Regards,
Crystal
Microsoft MVP
remote programming and training
Access Basics by Crystal
http://www.AccessMVP.com/strive4peace
Free 100-page book that covers essentials in Access
*
(: have an awesome day :)
*
________________________________
From: Isaac
Subject: [MS_AccessPros] Error received in VBA calculation of distance between geo coordinates
Pros: I know this is a shot in the dark, but my math skills are just not up to debugging this function. Thank you in advance for any thoughts/comments/suggestions:
We have a database of property locations which are geocoded and when a property is selected, one of the things the database does is it provides a list of neighboring properties, sorted by distance. Occasionally the database will throw an error: "Run-time error '5': Invalid procedure call or argument".
I choose to debug and it takes me to the function below (I used apostrophes to break out the function where the error is)
I know it is a mathematical error in that my function is generating a value that is out of range, but I can't figure out why one property (one set of coordinates) throws the error and why another does not.
For example a property with the coordinates of 40.9454923 , -72.8867217 throws the error while 40.9567969 , -72.9755829 does not. I can't figure out how to do the math in my head. I know there is a way to let the VBA editor go through the code step by step and display the values in the immediate window, but I can't get it to go through all the steps.
Thanks,
Isaac Richter
______________________________________
Option Compare Database
Option Explicit
' This routine calculates the distance between two points (given the latitude/longitude of those points). It is being
'used to calculate distance between two ZIP Codes or Postal Codes
'Definitions
' South latitudes are negative, east longitudes are positive
'Passed to function
'lat1, lon1 = Latitude and Longitude of point 1 (in decimal degrees)
'lat2, lon2 = Latitude and Longitude of point 2 (in decimal degrees)
'unit = the unit you desire for results where 'M' is statute miles (default)
' 'K' is kilometers
' 'N' is nautical miles
Const pi = 3.14159265358979
Global PropertyLat
Global PropertyLong
Public lngMap As Long
Global lngComparablesDistance As Long
Function Distance(lat1, lon1, lat2, lon2, unit)
Dim theta, dist
theta = lon1 - lon2
dist = Sin(deg2rad(lat1)) * Sin(deg2rad(lat2)) + Cos(deg2rad(lat1)) * Cos(deg2rad(lat2)) * Cos(deg2rad(theta))
dist = acos(dist)
dist = rad2deg(dist)
Distance = dist * 60 * 1.1515
Select Case UCase(unit)
Case "K"
Distance = Distance * 1.609344
Case "N"
Distance = Distance * 0.8684
End Select
End Function
*****************************
Below this is where the error is
*****************************
' This function get the arccos function from arctan function
'
Function acos(Rad)
If Abs(Rad) <> 1 Then
acos = pi / 2 - Atn(Rad / Sqr(1 - Rad * Rad))
ElseIf Rad = -1 Then
acos = pi
End If
End Function
*****************************
Above this is where the error is
*****************************
' This function converts decimal degrees to radians
'
Function deg2rad(Deg)
deg2rad = CDbl(Deg * pi / 180)
End Function
' This function converts radians to decimal degrees
'
Function rad2deg(Rad)
rad2deg = CDbl(Rad * 180 / pi)
End Function
'Demo
'response.Write distance(32.9697, -96.80322, 29.46786, -98.53506, "M") & " Miles<br>"
'response.Write distance(32.9697, -96.80322, 29.46786, -98.53506, "K") & " Kilometers<br>"
'response.Write distance(32.9697, -96.80322, 29.46786, -98.53506, "N") & " Nautical Miles<br>"
Function GetDistance(Latitude, Longitude)
If ((Not IsNull(PropertyLat)) And (Not IsNull(PropertyLong))) Then
GetDistance = Distance(PropertyLat, PropertyLong, Latitude, Longitude, "M")
End If
End Function
------------------------------------
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