{"id":3514,"date":"2009-09-01T03:00:02","date_gmt":"2009-09-01T08:00:02","guid":{"rendered":"http:\/\/blogs.scienceforums.net\/swansont\/?p=3514"},"modified":"2009-09-01T03:00:02","modified_gmt":"2009-09-01T08:00:02","slug":"my-turf","status":"publish","type":"post","link":"http:\/\/blogs.scienceforums.net\/swansont\/archives\/3514","title":{"rendered":"My Turf"},"content":{"rendered":"

Built onFacts: Time and Navigation<\/a><\/p>\n

Matt gives a brief summary of time and navigation. There’s one point that he glosses over, and it’s something that a lot of GPS summaries gloss over, to the point that they are misleading.<\/p>\n

All a GPS satellite does is eternally broadcast two continuously updated pieces of information: its position and the time on its atomic clock. Knowing that light travels at about 1 foot per nanosecond, we can calculate how far we are from the satellite to the foot, as long as the GPS clock is accurate to the nanosecond and we have a receiver that can handle such a precise signal.<\/p><\/blockquote>\n

Actually you can’t do this unless you have a synchronized clock, and unless you’ve done this already, in order to synchronize the clocks properly you have to know \u2026 [wait for it] \u2026 the distance to the satellite. Many of the explanations of GPS completely miss this little tidbit. If you haven’t got a synchronized clock, and all you have are the GPS signals, you need four<\/em> satellites to find your position. In practice four may not be necessary, because if you know your approximate position on the earth and have a topographic map, you can get the elevation from that, in which case three satellites is sufficient to get your position, to some level of uncertainty.<\/p>\n","protected":false},"excerpt":{"rendered":"

Built onFacts: Time and Navigation Matt gives a brief summary of time and navigation. There’s one point that he glosses over, and it’s something that a lot of GPS summaries gloss over, to the point that they are misleading. All … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[39,53,56],"tags":[],"class_list":["post-3514","post","type-post","status-publish","format-standard","hentry","category-physics","category-tech","category-time"],"_links":{"self":[{"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/posts\/3514","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/comments?post=3514"}],"version-history":[{"count":0,"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/posts\/3514\/revisions"}],"wp:attachment":[{"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/media?parent=3514"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/categories?post=3514"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/blogs.scienceforums.net\/swansont\/wp-json\/wp\/v2\/tags?post=3514"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}