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Converting Strings Into Decimal Degree Format

Below is a small utility routine and the corresponding documentation that will help convert a user-supplied string in degree, minute, second format (e.g. N 49 12' 12.3") and will return a double in the decimal degree format MapPoint expects.

Microsoft MapPoint can accept geographical coordinates on input (e.g. in the "Find" dialog: select Edit/Find and switch to the "Lat/Lon" tab) as well as display them in the location sensor window (Tools/Location sensor).

While the "Find" dialog is smart and can handle values entered as degrees, minutes and seconds (simply separate them with a blank) or as decimal degrees, the GetLocation function available to the programmer requires doubles in decimal format.

Sometimes, coordinates are available in degree, minute, second format though, or users would like to enter values in this more familiar format (e.g. because that is the format their GPS is set to).

This article presents a handy VB subroutine for the MapPoint programmer that accepts a string in DMS (degree, minute, second) format and will convert it to decimal format. The routine is called DMSVal (in analogy to the Visual Basic "Val" conversion function).

The signature of the function is as follows:

  Function DmsVal(ByVal strDms As String, bValid as Boolean) As Double

DMSVal tries to be tolerant about the format of the strDMS string it accepts on input. There may be leading and trailing blanks, an optional compass point (N, E, S, W), and values for degrees, minutes and seconds separated by arbitrary delimiters except comma and period.

The decimal separator may be both the decimal point (.) common in North America as well as the comma (,) used in Europe (no thousands separator allowed nor needed though)

If compass points South (S or s) or West (W or w) are encountered, the return value is negative according to the convention used in MapPoint.

The following are examples of valid DMS strings:

  N 49 1' 5.1"
  49/1/5.1
  E49d1m5.1s
  E49 1 5.1

DMSVal will set the "bValid" parameter to "False" if it could not convert the input string. A successful conversion is indicate by a bValid value of "True".

If you already have the values available in separate fields, the following function can be used:

   Function DmsValCalc(strCompassPoint As String, dblDeg As Double, _
                       dblMin as Double, dblSec as Double) As Double

DMSValCalc can be called directly with a compass point (N, E, S, W), and the degree, minutes and seconds values. It is used internally by DMSVal.

Here's the code:

There is also an online converter at: http://www.mp2kmag.com/latlong.asp

Discuss this story in the forum.

Author: Gilles Kohl
Email: gilles(AT)_deletethisincludingunderlines_compuserve.com
URL: http://www.procad.de
Gilles Kohl, a native of Luxembourg living in Germany, is a software development lead with PROCAD GmbH of Karlsruhe, Germany.

Mapping and especially GPS-related topics are a hobby - Gilles enjoys developing solutions for Microsoft MapPoint and his favorite outdoor occupation is confluence hunting.

As always, please direct questions to the newsgroup.



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