For most of January I have been working with an open source GIS mapping component called SharpMap. It's a cool tool, and very powerful, but being open source it - to some extent, -suffers from a lack of clear examples, particularly for programmers new to this type of programing (geospatial) .
Today I wanted to calculate the distance between to points on the earths surface. This is quite a difficult thing to do mathematically, but luckily for me in 1975 this fellow came up with a good answer. Even better is that this fine fellow wrote it up in a C# Class - so that saved me a few hours today ;-).
Anyway i thought it might be useful to show how I have put this into practice using VB.net. Enjoy!
Go to Mike Gavaghans website and down load his C# code. unzip it and copy the file called "Gavaghan.Geodesy.dll" from the "Dist" folder to your base folder for your solution. Then add a reference to it in your IDE. The following function takes 4 arguments and returns a distance between them in meters.
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Imports System
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Imports Gavaghan.Geodesy
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Public Class VincentyGeodeticProblems
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'//Answers is in meters!
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Shared Function Distance _
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(ByVal Loc1_X As Double, ByVal Loc1_Y As Double, _
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byval Loc2_X as Double, byval Loc2_Y as Double) _
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as Double
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' instantiate the calculator
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Dim geoCalc As New GeodeticCalculator()
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' select a reference elllipsoid
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Dim reference As Ellipsoid = Ellipsoid.WGS84
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' set loc 1 coordinates
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Dim Loc1 As GlobalCoordinates
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Loc1 = New GlobalCoordinates(Loc1_X, Loc1_Y)
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' set loc 2 coordinates
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Dim Loc2 As GlobalCoordinates
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Loc2 = New GlobalCoordinates(Loc2_X, Loc2_Y)
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' calculate the geodetic curve
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Dim geoCurve As GeodeticCurve = _
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geoCalc.CalculateGeodeticCurve(reference, Loc1, Loc2)
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return geoCurve.EllipsoidalDistance
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End function
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End Class
Then you can do all sorts of useful stuff!
