Thanks a ton, I will do so. best regards, Andrea
On Thu, Oct 25, 2012 at 4:20 PM, Martin Vermeer <[email protected]> wrote: > > Andrea, > > 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. > > http://www.ed.ac.uk/schools-departments/geosciences/people?cw_xml=person.html&indv=473 > > http://www.era.lib.ed.ac.uk/handle/1842/4726 > > ...and yes, if you're working with water, your heights better be good, > and referring to sea level :-) > > Martin > > > On Thu, 25 Oct 2012 15:28:24 +0200 > andrea antonello <[email protected]> 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). >> >> Thanks, >> Andrea >> >> >> >> On Thu, Oct 25, 2012 at 3:12 PM, Gordon Williams <[email protected]> >> wrote: >> > 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" <[email protected]> >> > To: <[email protected]> >> > 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 >> >> _______________________________________________ >> >> 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 _______________________________________________ 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
