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Convert a bearing in degrees to compass point

andieje
andieje asked
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Medium Priority
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Last Modified: 2012-05-07
Hello

I have a gps tracking system in a vehicle. It provides the position of the vehicle as a latitide and longitude coordinate using wgs84. Apparently the unit can provide a heading for the vehicle in degrees.

Firstly, how does it calculate the heading? I know you won't know for definite but you will probably have an intelligent idea. Perhaps it stores the previous gps position and then compares this to the current gps position and uses this to calculate a bearing?

Secondly, if I have a heading in degrees, how could i convert this into one of the 8 compass points from N, NE, E, SE, S, SW, W, NW

Many thanks
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Jaime OlivaresSoftware Architect
CERTIFIED EXPERT
Top Expert 2008

Commented:
>>Apparently the unit can provide a heading for the vehicle in degrees.
Every GPS can provide you the rhumb (it is not always the same as the heading, specially for air/sea vehicles), but calculating by yourself is not a trivial stuff, because GPS use to give inaccurate positions that causes false heading calculations. For this, there is an algorithm named "Kalman Filter" that eliminates the error by providing many samples as input to have a stable heading value as output.
Besides this, calculating compass coordinates is quiet easy. Which programming language?

Author

Commented:
Hi

I dont know what a rhumb is. I looked it up on google but it doesnt seem to be possible to get a laymans explanation. However, I'm not sure I need to know exactly what it is but I would like to convert it to a compass bearing. I am using vb.net 2005.

Many thanks
Jaime OlivaresSoftware Architect
CERTIFIED EXPERT
Top Expert 2008

Commented:
don't worry about rhumb versus heading, it should be the same for terrestrial applications. About compass algorithm, here is some implementation of my own:

Public Function Quadrant(ByVal degrees As Single) As String
    Dim AllQuadrants As String = "NNE,NE,NEE,E,SEE,SE,SSE,S,SSO,SO,SOO,O,NOO,NO,NNO"
    Dim Quadrants As String() = AllQuadrants.Split(","c)
   
    If degrees > 348.75 OrElse degrees <= 11.25 Then
        Return "N"
    End If
    Dim q As Integer = CInt(Math.Floor((degrees - 11.25) / 22.5))
    Return Quadrantes(q)
End Function

Author

Commented:
Thats brilliant. However I only need the 8 compass points in my question. I don't know how to modify the code you have supplied to restrict it to just those compass points.

I could do something 'rough' like assigning the more detailed compass points to a more general one
e.g. if function returns NNE then convert it to NE but it would be nicer and easier to read if i could modif the function ou supplied
Software Architect
CERTIFIED EXPERT
Top Expert 2008
Commented:
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Author

Commented:
many thanks
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