On Fri, Feb 6, 2009 at 1:31 PM, Jean Christophe Andr? <jean-christophe.andre at auf.org> wrote: > Tom Lancaster a ?crit : >> On Fri, Feb 6, 2009 at 10:25 AM, Nguyen Vu Hung <vuhung16plus at gmail.com> >> wrote: >> >>> I will do it when I return to Vietnam. However, I heard that GPS receivers >>> in Vietnam may get 9m of error in minimum. Is that right? >>> >> Why would VN be any different than another point on the globe? > May be because there is less GPS service satellites covering our area?
FWIW I routinely pick up 10 satellites here, often more (up to 18, I think). Accuracy only drops in built-up areas with poor sight lines. > >> For non-military use the US GPS system only has 10m accuracy. In practice >> (in my experience) the accuracy appears to be somewhat better than that. >> > Yes and it's easy to explain: we would only get the precision they allow > us to get if we used GPS in the conventional way. But in fact you can > triangulate your coordinates with more than 4 satellites (3 for > trilateration, 1 for time correction) and finally get a far better > precision (with up to 12 or even 20 satellites with modern receivers). > And that's exactly what do most modern GPS receivers, should I say "of > course" ?! ;-) > > As usual, more detailed informations are available here: > http://en.wikipedia.org/wiki/GPS > And this time also in Vietnamese: :-) > http://vi.wikipedia.org/wiki/H?_th?ng_??nh_v?_to?n_c?u > > -- > Jean Christophe "????" ANDR? ? ? ? Responsable technique r?gional > Bureau Asie-Pacifique (BAP) ? ? ? http://www.asie-pacifique.auf.org/ > Agence universitaire de la Francophonie (AuF) ? ? ? http://www.auf.org/ > Adresse postale : AUF, 21 L? Th?nh T?ng, T.T. Ho?n Ki?m, H? N?i, Vi?t Nam > T?l. : +84 4 9331108 ? Fax : +84 4 8247383 ? Cellul. : +84 91 3248747 > ? Note personnelle: merci d'?viter de m'envoyer des fichiers PowerPoint ? > ? ou Word, cf http://www.gnu.org/philosophy/no-word-attachments.fr.html ? > > > > _______________________________________________ > POST RULES : http://wiki.hanoilug.org/hanoilug:mailing_list_guidelines > _______________________________________________ > HanoiLUG mailing lists: http://lists.hanoilug.org/ > HanoiLUG wiki: http://wiki.hanoilug.org/ > HanoiLUG blog: http://blog.hanoilug.org/ >
