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Re^4: Perl and Solving Trig/Converting GPS to x,y Cords

by BrowserUk (Pope)
on Jan 09, 2013 at 13:57 UTC ( #1012491=note: print w/ replies, xml ) Need Help??


in reply to Re^3: Perl and Solving Trig/Converting GPS to x,y Cords
in thread Perl and Solving Trig/Converting GPS to x,y Cords

it's not generally true. A trivial example being several of the polar maps.

How many people are plotting GPS locations inside the artic/antartic circles?

Especially given that ionospheric signal path distortion renders GPS essentially unusable in those regions.


With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.


Comment on Re^4: Perl and Solving Trig/Converting GPS to x,y Cords
Re^5: Perl and Solving Trig/Converting GPS to x,y Cords
by roboticus (Canon) on Jan 09, 2013 at 14:06 UTC

    BrowserUk:

    There are plenty of people who would be interested in mapping at the poles: Penguin and Polar Bear researchers, Multi-mega-conglomocorp oil exploration teams, eskimos, extreme sunbathers, etc.

    I was unaware of the GPS difficulties, and the OP didn't really restrict the regions of interest...

    ...roboticus

    When your only tool is a hammer, all problems look like your thumb.

      I was unaware of the GPS difficulties,

      Even without GPS inaccuracies at those latitudes; extraordinary measures need to be taken in the polar regions anyway.

      The same Law of Cosines Spherical Geometry that work just fine for larger distances over most of the Earth's surface are entirely inadequate in polar regions.

      For more details, see the GIS FAQ.


      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.

        BrowserUk:

        Correct, and that's in line with what I'm saying: The law of cosines isn't involved in the conversion from 3D to 2D in all projections--it's inadequate to the task. Further in the FAQ it talks about the Haversine formula which suffers when the points are extremely far apart, rather than being close to the poles. All spherical to planar mappings suffer in one way or other. Without knowing what type of map the OP is using, we can't be certain in exactly which ways it will suck. 8^)

        Even when the law of cosines is used, the Z-axis isn't always the the same as either the geographic N/S axis or the magnetic N/S axis. It all depends on the feature(s) the map is trying to portray.

        ...yet another pedantic weenie

        When your only tool is a hammer, all problems look like your thumb.

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