diff options
author | Sanjeev Gupta <ghane0@gmail.com> | 2013-11-25 16:20:42 +0800 |
---|---|---|
committer | Eric S. Raymond <esr@thyrsus.com> | 2013-11-25 04:22:17 -0500 |
commit | cb2fd70d2e0c14d53d0585e3145ee08be8aa6322 (patch) | |
tree | 5da70d30236d042b540613f9a0ba73b24639b4ef /www | |
parent | 2c9477d6677f5a4840c6d9a6f9fc2685921544db (diff) | |
download | gpsd-cb2fd70d2e0c14d53d0585e3145ee08be8aa6322.tar.gz |
Correct Almanac / Ephermis confusion
Signed-off-by: Eric S. Raymond <esr@thyrsus.com>
Diffstat (limited to 'www')
-rw-r--r-- | www/faq.html.in | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/www/faq.html.in b/www/faq.html.in index 215ce1ca..89f6a62b 100644 --- a/www/faq.html.in +++ b/www/faq.html.in @@ -531,14 +531,14 @@ second.</p> <p>If you are starting a GPS for the first time, or after it has been powered off for more than two weeks, this is a 'cold start'; it needs -to get a new satellite ephemeris to do its job. The satellites +to get a new satellite <i>almanac</i> to do its job. The satellites broadcast this information very slowly (at 50bps) on a fixed schedule, and it can take up to 20 minutes.</p> <p>Warm start on a modern GPS with a good skyview (4 or more sats visible) normally takes about 30 seconds. (Vendor spec sheets fib by quoting this time only, leaving out the cold-start lag to fetch -ephemeris.) If it's taking longer, the first thing to suspect is that +almanac.) If it's taking longer, the first thing to suspect is that your skyview is poor. Especially if you're indoors.</p> <p>The best advice is: go outside and be patient for a few minutes.</p> @@ -547,14 +547,14 @@ your skyview is poor. Especially if you're indoors.</p> <p>Your GPS may have dropped its leap-second offset. You can tell you have this problem if your sentence timestamps look wrong at startup. -Wait 20 minutes or so; the lag should go away.</p> +Wait 20 minutes or so; the lag should go away, as the almanac is updated.</p> <p>GPS satellites broadcast time using a clock without a leap-second correction. They broadcast a leap-second correction once each complete -reporting cycle along with the satellite ephemerides; it's up to the +reporting cycle along with the satellite almanac; it's up to the GPS firmware to add that correction to the time it puts in reports. If your GPS has forgotten the current correction, you'll have to wait -until the next ephemerides message for it.</p> +until the next almanac message for it.</p> <p>GPSes are supposed to retain the leap-second correction along with the last fix in NVRAM when they power down, but we've observed that |