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  1. #1
    Platinum Lounger
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    absolute latitude longitude? (algorithms)

    (If there is a more suitable forum for "algorithms" please move this thread to that forum)

    I'm developing some geographic code. I deal in latitude/longitude, such as "43N 80W" or "32S 120W".

    Traditional lat/long is relative to the Greenwich meridian and is relative to the equator.

    Is anyone aware of a scheme for absolute coordinates?

    I could arbitrarily start at Greenwich and go east, so that New York would be 180+(180-75) or 285E, and I could start at the North Pole and go south, so that New York would be at 40S and Perth (Australia) would be at 90+132 = 122S.

    On the other hand, why start my own system if there is an acknowledged standard already being used?


    Who is programming these GIS devices, and what do they use? I could think back to 1960 high school days and use Radian measure if I had to; My location tables are built but once, and could be converted from latNS/longEW to radins (or any suitable system) at the time of data entry.

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    Re: absolute latitude longitude? (algorithms)

    If you are looking to invent your own system, and want something that would be easy in calculations, then you could start at the center of the earth and use X,Y,Z cordinates for points on the surface.
    Legare Coleman

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    Re: absolute latitude longitude? (algorithms)

    > If you are looking to invent your own system

    Sheesh! Legare, you've seen me invent program code; if I invent a means for knowing where we all are, then we'd be lost (grin!).


    I'd rather not invent a system if there is an existing standard, any standard.

    The XYZ co-ordinates sounds suspicially like radian measure. I still have my slide rule and log tables, but w as hoping for something simpler.



    For the time being I have adopted a measurement East of Greenwich and South of the North Pole on the grounds that I can easily convert it back to the original NS, EW method if I want to migrate to a standard system.

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    Re: absolute latitude longitude? (algorithms)

    But that means you have to use a 360 degree coordinate instead of the +/- 180 degree that lat/lon uses. So you'll have to build a whole system for handling these non-standard coordinates and some method for translating them to and from standard lat/lon, right? To what purpose? It becomes particularly tricky as the poles shift. <img src=/S/evilgrin.gif border=0 alt=evilgrin width=15 height=15>
    Charlotte

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    Re: absolute latitude longitude? (algorithms)

    This site looks to have a bunch of resources: http://www.gpsy.com/gpsinfo/index.html

    And possibly:
    http://www.auslig.gov.au/geodesy/datums/calcs.htm (Would the <img src=/S/aussie.gif border=0 alt=aussie width=21 height=22>'s let you down?)
    http://www.zend.com/codex.php?CID=12

    And maybe if you ask nicely these folks can help:
    http://www.cellspark.com/
    http://www.uwgb.edu/dutchs/FieldMethods/UTMSystem.htm
    -John ... I float in liquid gardens
    UTC -7ąDS

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    Re: absolute latitude longitude? (algorithms)

    Chris, the standard is 0 is Greenwich, going east is +, going west is -.
    Also the equator is 0, going north is +, going south is -. So, your area, Toronto, is 43,-79. Some other links:
    http://terraserver.homeadvisor.msn.com/default.aspx (US only, sorry!)
    http://mac.usgs.gov/mac/isb/pubs/fac...s/fs07701.html
    http://www.geocomm.com/
    <font face="Comic Sans MS">Sam Barrett, CACI </font face=comic>
    <small>And the things that you have heard... commit these to faithful men who will be able to teach others also. 2 Timothy 2:2</small>

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    Re: absolute latitude longitude? (algorithms)

    > the standard is 0 is Greenwich, going east is +, going west is -

    Sam, thanks. I'll switch to that. It makes more sense than my arbitrary "360 going east from Greenwich and 180 going south from North Pole" scheme.

    Please don't apologise for the links. The "Us Only" is fascinating, as I can revisit each of the fifty states at my leisure now!

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    Re: absolute latitude longitude? (algorithms)

    Thanks, John. The samples of UTM-conversion seem way to unweildy for me.

    I might grab hold of them for a spreadsheet class example though. Should keep the front row quiet (grin!)

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    Re: absolute latitude longitude? (algorithms)

    If I remember correctly, UTM is what GIS applications use, although they present lat/lon coordinates for human understanding.
    Charlotte

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    Re: absolute latitude longitude? (algorithms)

    > UTM-conversion seem unweildy
    unweildy is an understatement! Moreover, every one that I have tested has only been an approximation. To do the job correctly, you need GeoTrans from NIMA.

    > The "Us Only" is fascinating
    Yes, TerraServer is very useful and fun. However, it dosn't do addresses very well: it only seems to get you within a couple of blocks of the actual location.
    <font face="Comic Sans MS">Sam Barrett, CACI </font face=comic>
    <small>And the things that you have heard... commit these to faithful men who will be able to teach others also. 2 Timothy 2:2</small>

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