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Newbie question on plotting lat/lon

This is a discussion on Newbie question on plotting lat/lon within the MapPoint Desktop Discussion forums, part of the Map Forums category; I work for a medical helicopter and want to plot several years worth of response data on a map. I ...

  1. #1
    swthurmond is offline Junior Member White Belt
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    Newbie question on plotting lat/lon

    I work for a medical helicopter and want to plot several years worth of response data on a map. I have a simple excel spreadsheet with two columns - lat and lon - in this format 2819.50'N and 08124.50'W. No matter what I do none of my points get matched. They all say skipped and I cannot make them match. I have also tried it with the corresponding state and zip code information and still have no luck. I can post the spreadsheet if needed. Thanks in advance for your help.

  2. #2
    Winwaed's Avatar
    Winwaed is offline Mapping-Tools.com Black Belt
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    Re: Newbie question on plotting lat/lon

    MapPoint needs the coordinates to be in decimal degrees on the WGS84 geoid. There's a good chance your coordinates are already WGS84 but you should check. This result in an error of 1-200m or so. WGS84 is supported by most GPS systems, and is the geoid used by the satellites themselves.

    Your main problem is the actual formatting of the coordinates.
    These need to be in decimal degrees and not minutes and arcs of second. Your coordinates are degrees, minutes. It looks like the number after the "." is just the decimal minutes (check if you can: it might be seconds of arc).
    To convert:

    Decimal degrees = Degrees + (minutes of arc)/60 + (seconds of arc)/3600

    You also need to change the N & W into signed numbers.
    The Northern Hemisphere has POSITIVE latitudes, and the Western Hemisphere has NEGATIVE longitudes.


    Richard
    Winwaed Software Technology LLC
    http://www.winwaed.com
    See http://www.mapping-tools.com for MapPoint Tools

  3. #3
    swthurmond is offline Junior Member White Belt
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    Re: Newbie question on plotting lat/lon

    I wondered if that might be the case. Nowhere that I could find stated the necessary format. And since we are aviation based, we still primarily use DMS as opposed to decimal degrees. Looks like I get to parse the data in Excel and then do that calculations from there. Thanks for the answer.

  4. #4
    Wilfried is offline Senior Member Black Belt
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    Re: Newbie question on plotting lat/lon

    Hi,

    2819.50'N and 08124.50'W is certainly dd mm.ff Where ff is the fractions of the arc minute and not the arc second.

    I just phoned to my sun who is B737 pilot to ask what the common habitude is, and he tell that all the coordinates (in Europe) are always in that format.

  5. #5
    swthurmond is offline Junior Member White Belt
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    Re: Newbie question on plotting lat/lon

    Yep. as he said most aviation is just that. I have always said DMS even though it is actually as you sad - DMMFF. Most people look cross-eyed when you talk about fractional minutes. They get even more crossed when you say the final numbers as anything above 59 - how can there be more than 59 seconds in a minute!!

    So there is still no way to import the raw data even though it is not decimal degrees?

  6. #6
    Wilfried is offline Senior Member Black Belt
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    Re: Newbie question on plotting lat/lon

    Hi,

    Yes you can. You have to convert it first. You can do that in Excell as whell and then import it, or you can use Mappoint from within Excell as whell.

  7. #7
    Eric Frost's Avatar
    Eric Frost is offline Administrator Black Belt
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    Re: Newbie question on plotting lat/lon

    Hey, just thought I'd add, there is Gilles Kohl's library for converting programmatically, also see the tool on Directions Magazine for testing/double-checking individual conversions --

    Latitude / Longitude DMS -> Decimal Converter

    Eric

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