# Re: [OpenMap Users] Measuring Distance on Map

From: F.Bayliss <bayliss_at_alcatel-lucent.com>
Date: Fri, 01 Jun 2007 11:04:59 -0400

Don,

What you said make perfect sense. But, the map shown on the screen is
flat and not wrapped around the globe. When I display the Graticule
layer the distance (in pixels) between the Longitude lines are the same
as you go north/south. So isn't the mileage the same also?.

Thanks
Frank

Don Dietrick wrote:
> Hi Frank,
>
> The distance measurements have nothing to do with the projection.
> They are based, rightfully so, on elipsoid (Geo) and spherical
> (GreatCircle) models. As you move north, distances between longitudes
> get smaller (look at a globe with graticule lines and measure the
> physical distance on the globe between longitude lines).
>
> Hope this helps,
>
> Don
>
> On May 31, 2007, at 9:55 AM, F.Bayliss wrote:
>
>> All,
>>
>> I'm confused. I'm using the Mercator projection and displaying the US
>> in my application. I wanted to know the distance (miles and
>> kilometers) between two points. I've tried using Geo.distanceNM & KM
>> and I even copied some code from DistanceMouseMode using
>> GreatCircle.spherical_distance. What I've found is the distance
>> between two identical length longitudinal lines at different
>> latitudes have different length. Why? Isn't the map displayed flat so
>> the width, lets say - Wyoming being close to square, is the same
>> width at the top and bottom borders? Help.
>>
>> Thanks
>> Frank
>>
>> --
>> [To unsubscribe to this list send an email to "majdart_at_bbn.com"
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>
>
>
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Don Dietrick, dietrick_at_bbn.com
> BBN Technologies, Cambridge, MA
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>
>

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Received on Fri Jun 01 2007 - 11:04:35 EDT

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