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acid2000
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Joined: Nov 13, 2005
Posts: 10
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 Posted: Mon Aug 21, 2006 3:53 pm Post subject: Long/Lat to graph/map |
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I'm trying to convert longditude/latitude data into a graph. Given that the data will be for an area < 500km a flat earth approximation seems good.
What is the best way to convert my data to cartesian XY coordinates?
The current method I'm using seems off when compare to http://www.gpsvisualizer.com.
Thanks for any help |
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lbendlin
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Joined: 02/11/2002 22:41:59
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Location: Massachusetts, USA
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| Posted: Mon Aug 21, 2006 10:53 pm Post subject: |
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Keep in mind that you won't have a rectangle, even if you assume a flat earth. The longitude lines will be straight (but not parallel!) but the latitude lines won't
500 km is already way too much to neglect that.
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acid2000
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| Posted: Tue Aug 22, 2006 1:17 pm Post subject: |
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Sorry wrong number, my data is within 1mile.
The graph I have is similar to that of gps visualiser but seems in the wrong aspect ratio. Is there not a stock formular for conversion? |
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David_A_James
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Joined: Apr 27, 2006
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| Posted: Tue Aug 22, 2006 6:03 pm Post subject: |
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| acid2000 wrote: | Sorry wrong number, my data is within 1mile.
The graph I have is similar to that of gps visualiser but seems in the wrong aspect ratio. Is there not a stock formular for conversion? |
Whereabouts in the world is your data?
If it's in the UK, the Ordnance Survey website has formulae for converting from lat/long to OSGB eastings and northings. |
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David_A_James
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Joined: Apr 27, 2006
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| Posted: Tue Aug 22, 2006 6:08 pm Post subject: |
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| David_A_James wrote: | | acid2000 wrote: | Sorry wrong number, my data is within 1mile.
The graph I have is similar to that of gps visualiser but seems in the wrong aspect ratio. Is there not a stock formular for conversion? |
Whereabouts in the world is your data?
If it's in the UK, the Ordnance Survey website has formulae for converting from lat/long to OSGB eastings and northings. |
There's a spreadsheet containing these at http://www.bangor.ac.uk/is/isx025/osgb.xls courtesy of Phil Brady who also has a FAQ on this topic at http://www.bangor.ac.uk/is/isx025/osgbfaq.htm |
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lbendlin
Pocket GPS Staff
Joined: 02/11/2002 22:41:59
Posts: 11878
Location: Massachusetts, USA
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| Posted: Tue Aug 22, 2006 6:23 pm Post subject: |
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| acid2000 wrote: | | Is there not a stock formular for conversion? |
If you are in the lower part of the UK then you can roughly assume a ratio of 1 to 0.6 for latitude to longitude.
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Lutz
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harryparkes
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Joined: Sep 17, 2006
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| Posted: Sun Sep 17, 2006 8:22 pm Post subject: |
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Hi,
A bit late in replying.
To get the correct aspect ratio divide the longitudinal difference by the cosine of the mid-latitude. So for lat 50 deg the factor is cos 50 = 0.64279.
Harry |
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harryparkes
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Joined: Sep 17, 2006
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| Posted: Sun Sep 17, 2006 8:29 pm Post subject: |
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Not only late but wrong! I should have said mutiply.
Harry |
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