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VB.net form for converting DMS to Decimal Degrees

Posted on 2013-05-21
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568 Views
Last Modified: 2013-05-22
I'm trying to create a simple form to convert degrees minutes seconds to decimal degrees, but I'm having trouble when converting negative numbers.  When I try to convert -92 7 6.52 I get -91.8815222 but the answer should be -92.118478.  Why is this simple formula not working?
Private Sub btnDecimal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDecimal.Click

        'txtLatDecimal.Text = Math.Round(CInt(txtLatDegrees.Text) + (CInt(txtLatMin.Text) / 60) + (CDec(txtLatSec.Text) / 3600), 7)

        'txtLngDecimal.Text = Math.Round(CInt(txtLngDegrees.Text) + (CInt(txtLngMin.Text) / 60) + (CDec(txtLngSec.Text) / 3600), 7)

        txtLatDecimal.Text = Math.Round(((CDec(txtLatSec.Text) / 60) + CInt(txtLatMin.Text)) / 60 + CInt(txtLatDegrees.Text), 7)
        txtLngDecimal.Text = Math.Round(((CDec(txtLngSec.Text) / 60) + CInt(txtLngMin.Text)) / 60 + CInt(txtLngDegrees.Text), 7)

    End Sub

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Question by:Nate_LR
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LVL 23

Expert Comment

by:Ioannis Paraskevopoulos
ID: 39185999
Hi,

You are adding positive numbers to negative, so the result is closer to zero:
6.52/60+7/60-92 results to -91.8815222.

Giannis
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LVL 44

Expert Comment

by:Arthur_Wood
ID: 39187105
You need to determine the sign of txtLngDegrees.Text and then apply that sign to the other parts of your formula. Thus your formula would become

-6.52/60 - 7/60 - 92 = -92.118478

AW
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LVL 44

Accepted Solution

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Arthur_Wood earned 500 total points
ID: 39187249
try this:

Dim signLng as Integer = CInt(txtLngDegrees.Text)/Abs(CInt(txtLngDegrees.Text))
Dim signLat  as Integer = CInt(txtLatDegrees.Text)/Abs(Cint(txtLatDegrees.Text))

        txtLatDecimal.Text = Math.Round((( signLat*CDec(txtLatSec.Text) / 60) + signLat*CInt(txtLatMin.Text)) / 60 + CInt(txtLatDegrees.Text), 7)
        txtLngDecimal.Text = Math.Round((signLng*(CDec(txtLngSec.Text) / 60) + signLng*CInt(txtLngMin.Text)) / 60 + CInt(txtLngDegrees.Text), 7)

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Author Closing Comment

by:Nate_LR
ID: 39188342
Thanks
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LVL 44

Expert Comment

by:Arthur_Wood
ID: 39188354
Glad to be of assistance.

AW
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