Re: Google Earth: Elevation of water?

On Thu, 01 Sep 2005 06:58:08 +0100, Terry Pinnell
<terrypinDELETE@xxxxxxxxxxxxxxxxxxx> wrote:

>Stan Gosnell <me@xxxxxxxx> wrote:
>
>>Terry Pinnell <terrypinDELETE@xxxxxxxxxxxxxxxxxxx> wrote in
>>news:rdv6h1l2o223i7167lggrc290deb4u7pog@xxxxxxx:
>>
>>> Maybe you misread my post. I was asking why GE reported a small lake's
>>> surface at 'elevations' varying widely (50 ft or so) across a few
>>> hundred feet horizontally. I was guessing it must be reporting
>>> *ground* elevations.
>>>
>>GPS reports the elevation it *thinks* it is above MSL, whether it's on
>>water, land, or anything else. The receiver doesn't know the elevation of
>>any point, but gets the elevation from the satellites. This is very
>>imprecise, and varies with the satellite geometry. This is the reason for
>>WAAS, to provide altitude with greater precision for aircraft, not for
>>greater horizontal precision. That is just a side effect. You will see
>>different altitude reported at the same place, depending on the time and
>>the satellites received, and their relative locations. Altitude is far
>>less accurate than horizontal location.
>
>Thanks. It's plainly a pretty complex issue. But the inconsistencies
>between USA and UK still puzzle me greatly. As you probably saw from
>my reply to Peter, I've now tested many (a score or so to date) of
>lakes in each country. GE reports *all* the US lakes with flat
>elevations, and *none* of the UK lakes.

Maybe Google was guessing because they didn't want to pay for
the "Crown's proprietary information" gathered by your government, as
opposed to the free information gathered by the US governmnet.

> Many of the latter, like the
>one that prompted the thread, Ardingly, have really wide variations
>across relatively short horizontal distances.
>
>IMO, GE water elevation data for UK seems largely worthless.

.

Relevant Pages

  • Re: Google Earth: Elevation of water?
    ... I was guessing it must be reporting ... GPS reports the elevation it *thinks* it is above MSL, ... but gets the elevation from the satellites. ... WAAS, to provide altitude with greater precision for aircraft, not for ...
    (sci.geo.satellite-nav)
  • Re: Race Report & Travelogue - Bizz Johnson Trail Half Marathon
    ... have almost as much effect as 3000ft elevation. ... Martin and Coe was the only book I had with citations for altitude ... The limit to VO2max ... Robert Grumbine http://www.radix.net/~bobg/ Science faqs and amateur activities notes and links. ...
    (rec.running)
  • Re: Contador considers Armstrong and Leipheimer Tour rivals
    ... lack in severity they make up in elevation. ... won't qualify as "screwing around". ... there's a downside to training at altitude. ... to ride hard, hit threshold, and elevate your HR. ...
    (rec.bicycles.racing)
  • Re: Race Report & Travelogue - Bizz Johnson Trail Half Marathon
    ... "effects of altitude on marathons" gives a number of scholarly articles ... We examined the effect of altitude up to 5200 m on marathon ... plus a sea level marathon. ... 100 m (and ignoring any critical elevation for starting the effect) suggests ...
    (rec.running)
  • Re: Contador considers Armstrong and Leipheimer Tour rivals
    ... But they're on road bikes. ... won't qualify as "screwing around". ... I was referring to the benefits of training at elevation, ... there's a downside to training at altitude. ...
    (rec.bicycles.racing)
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