"Sunshine" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Mon, 6 Jun 2011 22:36:19 -0600, "H-M"
> <(E-Mail Removed)> wrote:
>
>>
>>"Gene E. Bloch" <(E-Mail Removed)> wrote in message
>>news:(E-Mail Removed)...
>>> On 6/06/2011, Gene E. Bloch posted:
>>>> On 6/06/2011, Guess posted:
>>>>> "Moonraker" <(E-Mail Removed)> wrote in message
>>>>> news:isiq70$q3$(E-Mail Removed)...
>>>>>> Out walking a steep hill today I just wondered, starting at A
>>>>>> climbing
>>>>>> up a steep hill then down the other side to B what will my Gps60csx
>>>>>> show, distance that I have walked or the horizontal distance from A
>>>>>> to
>>>>>> B? If the latter then the speed will be reduced as well, as it relies
>>>>>> on
>>>>>> satellite positioning I would expect it to be the shorter distance,
>>>>>> however as it also tells me how much climbing I have done perhaps it
>>>>>> is
>>>>>> cleverer than that.
>>>>>> -- Residing on low ground in North Staffordshire
>>>
>>>>> I can't comment on what "actually" happens but there is no reason why
>>>>> it
>>>>> should get distance and speed wrong as height is known to the gps and
>>>>> I
>>>>> would seriously hope that it is taken into account!
>>>
>>>>> Iain,
>>>
>>>> I would agree, except that typically height is pretty inaccurate for
>>>> reasons frequently discussed[1] on the GPS newsgroups.
>>>
>>>> The slope would have to be pretty steep for the difference between
>>>> sqrt(x^2 + y^2) and sqrt(x^2 + y^2 + z^2) to be significant.
>>>
>>> Let's say x=100, y=120, z=20, or almost a 13% slope.
>>>
>>> Ignoring z we get 156.205.
>>> With z, we get 157.480, under a 1% difference.
>>>
>>>> [1] But AFAICT, not really explained :-)
>>>
>>> --
>>> Gene E. Bloch (Stumbling Bloch)
>>>
>>>
>>Some time ago I asked Garmin the very same question. I even sent them a
>>track log and the Mapsource T&WPM elevation plot of the track log. Using
>>the
>>scale on the X axis and a divider you can determine the total distance you
>>travel accounting for an elevation gain.
>>In my case this can be quite significant because on a hike in the
>>mountains
>>I frequently accend 700 metres.
>>The Garmin rep I spoke to took a while to respond because he passed the
>>data
>>on to Garmin Cartography.
>>Their answer was as follows:
>>
>>"Thank you for contacting Garmin Cartography and I apologize. I thought
>>I had already responded. I did check with engineering and the track log
>>recorded by our units does not take into account vertical distance
>>travelled. It will only calculate the distance travelled between track
>>log points based on lat/long. Elevation is not factored in."
>>
>>So that means that the any speed you measure is not correct either since
>>it
>>is just measuring the X axis.
>>That is a distance between two point on an imaginary sphere representing
>>the
>>surface of the earth.
>>So even though the GPS may know the elevation it is not that smart.
>
> I'm probably wrong, but the way I parse the Garmin reply it looks like
> the answer is limited to what's captured in the track log. I can't
> tell if it extends beyond that or not.
>
You are correct . In the discussion I had with the Garmin Rep, we reviewing
the material I sent him.
If you load up a track, Mapsource can print out a distance (x axis)
elevation (y axis) profile.
The horizonal x axis is the sum of the point to point track log distances.
The vertical distance is the altitude as recorded from an altitude the GPS
is able to resolve,
provided it is getting reading from three or more satellites.
The altitude recording can get pretty erratic because it is a calculation.
Now it you take a divider and set the points to some convenient scale (1
km ) from the x axis.
Now it you take the divider and space it over the slope on the print out you
have a better idea
of the distance you really travelled.
Compare that divider measurement to the x axis distance and you will see a
significant difference
provided there was also an elevation gain in your track.
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