[FOSS-GPS] GPS issues for Ethiopia
andrea.antonello at gmail.com
Thu Oct 25 07:30:36 PDT 2012
Thanks a ton,
I will do so.
On Thu, Oct 25, 2012 at 4:20 PM, Martin Vermeer <martin.vermeer at aalto.fi> wrote:
> you may want to contact Professor Roger Hipkin of Edinburgh University
> who has been involved for many years in geoid determination also
> related to Ethiopia if I remember well.
> ...and yes, if you're working with water, your heights better be good,
> and referring to sea level :-)
> On Thu, 25 Oct 2012 15:28:24 +0200
> andrea antonello <andrea.antonello at gmail.com> wrote:
>> Hi Gordon,
>> thanks for your feedback.
>> I think I have not been clear about what my problem is.
>> I am aware what the problems with the geoid implications are.
>> My question was more related to some missing data in the Ethiopian
>> region, since they told me that there is a big hole, of which I wa
>> snot aware.
>> From the answers I am getting I see that also in those African regions
>> there are the same problems that we have in every world region, when
>> it come to altimetry measurements, geoid and precision. so no need to
>> worry (more than the usual).
>> On Thu, Oct 25, 2012 at 3:12 PM, Gordon Williams <gwilliams at ncf.ca>
>> > There are converters that will take GPS ellipsoidal height and give
>> > you Orthometric height based on the Geoid for a specific Long/Lat.
>> > UNAVCO has one
>> > http://www.unavco.org/community_science/science-support/geoid/geoid.html
>> > Example output
>> > Your Input Coordinates and GPS Height:
>> > Latitude = 9.026958° N = 9° 1' 37.05" N
>> > Longitude = 38.72371° E = 38° 43' 25.36" E
>> > GPS ellipsoidal height = 100 (meters)
>> > Geoid height = -7.392 (meters)
>> > Orthometric height (height above mean sea level) = 107.392 (meters)
>> > (note: orthometric Height = GPS ellipsoidal height - geoid height)
>> > This is based on a mathematical model of the Geoid, so you would
>> > have to look into how accurate that model is and if your region
>> > fits the model well. The Geoid is affected locally by gravitational
>> > changes from mountains and ground density. Check out wikipedia for
>> > geoid and orthometric height.
>> > You should get a book on surveying and talk to your local university
>> > surveying department.
>> > Gordon Williams
>> > ----- Original Message -----
>> > From: "andrea antonello" <andrea.antonello at gmail.com>
>> > To: <foss-gps at lists.osgeo.org>
>> > Sent: Thursday, October 25, 2012 7:19 AM
>> > Subject: [FOSS-GPS] GPS issues for Ethiopia
>> >> Hi I need some information about the above subject.
>> >> We are planning a educational project for water management
>> >> networks in Ethiopia and we applied to get a precision GPS to do
>> >> the surveys.
>> >> We just got hit by one very upset persons responsible for the
>> >> project that told us that a professor of topography explained them
>> >> that: "since in Africa there is not geoid, the GPS is useless"
>> >> Apart of the citation, which may rise some comments on its own, I
>> >> was wondering if there is something I am not considering and
>> >> should really know. We have used gps in Rwanda without problems
>> >> for the same purposes and I am quite puzzled about what I am
>> >> missing.
>> >> Any advice or link to documentation is very appreciated,
>> >> Thanks,
>> >> Andrea
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