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| Subject: | RE: GISList: DD to Metric |
| Date: |
01/07/2003 11:20:54 AM |
| From: |
Simmonds, Ashley (PTB) |
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i'm not a guru with this stuff, i've setup my own procedures for doing this
though and as far as i can tell there is no SET conversion method, because 1
degree of long/lat is a different distance depending where on the planet you
are.
if, like me, you're calculations are based in a specific area localized
enough so that you don't have to work with a curved earth calculation model
(within a few hundred kilometres or so) then the easiest way is to first
determine how many metres in 1 degree of lat/long, then it's just a matter
of division. for the method for determining the distance of a degree you
will need to seek other help, my calculations are area specific so i just
used MapInfo to determine the distance once.
within my programs, i have some constants set up which are currently
hardcoded into it, as it always expects locations within a specified zone,
so i have something like this declared in my module:
##################
Public Const XDegrees2Metres As Double = 91163.7427419522 ' the number of
metres in a degree of latitude in adelaide metro area
Public Const YDegrees2Metres As Double = 111198.387139005 ' the number of
metres in a degree of longitude in adelaide metro area
##################
then, if the calculation were based on ONLY one axis (ie. 0.019858 along the
X axis, so i want to know how far it is from 138.6 to 138.619858) then it's
just:
##################
0.019858 * XDegrees2Metres = 1810.3 metres
##################
which is to say 138.619858 is 1810.3 metres due East of 138.6, however
0.019858 degrees south = 2208.2 metres.
if you want to calculate that distance on an angle then there's a lot more
involved. you will need the start and end X and Y, and the calculation will
basically be this:
##################
Sqr((((X1 - X2) * XDegreesToMetres) ^ 2) + (((Y1 - Y2) * YDegreesToMetres) ^
2))
##################
take note that this is a specifically flat earth model calculation.
ash.
-----Original Message-----
From: Anthony Quartararo [mailto:ajq3@spatialnetworks.com]
Sent: Friday, 27 December 2002 2:57 PM
To: gislist@geocomm.com
Subject: GISList: DD to Metric
Anyone have the linear conversion for Decimal Degrees units to Metric units
such as meters or km ? For example, I have a DD measurement of .019858 and
would like to convert that to Km preferably. Thanks in advance.
Anthony
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