Le 10/05/2012 21:50, Jim Lux a écrit :
On 5/10/12 9:18 AM, Chris Albertson wrote:
On Thu, May 10, 2012 at 9:07 AM, Bob Camp<[email protected]> wrote:
.
Hi all,
Hope this isn't too chat roomy, however, I have need of a survey
precise
geolocation type gps. I was wondering if the precise timing abilities
extend to its precision in position output? I have a thunderbolt and
one of those conical white aerials from china and would like to know if
this combination will give me accurate height data.
It will give "pretty good" height data. Within a few meters but you
have to know how to translate between different definitions of "sea
level" to make best use of the data.
I found an online WGS84-MSL converter at:
<http://earth-info.nga.mil/GandG/wgs84/gravitymod/wgs84_180/intptW.htm>
however for my location this gives the geoid height at 51,89m wrt MSL
and if I apply that to my Z3801A reported height it make the difference
with my TBolt even greater. I had read elsewhere , though I can't find
the reference, that the difference at my latitude is more like 30m which
would make more sense.
Can someone with a Z3801A check the result for their location?
If you live in the USA you can now download for free the USGS
topographic maps. I'm pretty sure thy have full coverage of all of
the US. THese will have 20 foot contour intervals and you can
interpolate to at least half that. So for most normal purposes you
can find your elevation without a GPS. Just look on the topo map.
Most of these maps where made with stereo camera pairs. They get
relative elevation optically by matching the two images and then they
sent survey teams to ground check some points.
And updated the elevation data with radar measurements from SRTM, as
well.
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