Hi Antonio, thanks for the reply, > GPS geodetic ellipsoidal coordinates (latitude, longitude and height) are > relative to an ellipsoid (WGS84). Computation of GPS height differences is > not a true topographic levelling because GPS heights are relative to the > ellipsoid surface (+ above or - below). Topographic levelling uses gravitic > equipotential surfaces (the Geoid is one of this kind). The water flows > (when not using water pumps) due to gravity. So for open channel water > supply systems true levelling is almost mandatory.
I agree with this. Even if here we are talking about pressurized pipes, a quite precise elevation is necessary. The idea is to do some relative measurement for the vertical component. But I should really not have any issue with the horizontal positions. Thanks, Best regards, Andrea > > Best regards > > Antonio > > 2012/10/25 andrea antonello <[email protected]> >> >> 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 >> _______________________________________________ >> This message is sent to you from [email protected] mailing list. >> Visit http://lists.osgeo.org/mailman/listinfo/foss-gps to manage your >> subscription >> For more information, check http://wiki.osgeo.org/wiki/FOSS-GPS > > > > _______________________________________________ > This message is sent to you from [email protected] mailing list. > Visit http://lists.osgeo.org/mailman/listinfo/foss-gps to manage your > subscription > For more information, check http://wiki.osgeo.org/wiki/FOSS-GPS > _______________________________________________ This message is sent to you from [email protected] mailing list. Visit http://lists.osgeo.org/mailman/listinfo/foss-gps to manage your subscription For more information, check http://wiki.osgeo.org/wiki/FOSS-GPS
