In message <[EMAIL PROTECTED]>, "M. Warner Losh" writes: >In message: <[EMAIL PROTECTED]> > Rob Seaman <[EMAIL PROTECTED]> writes: >: The question is whether "at least 20 minutes" (presuming this to be >: accurate) is intrinsic to the system design or is rather a result of >: poor implementation by some receiver manufacturers. > >A cold GPS receiver takes about 20 minutes to get the almanac data >from the GPS constellation. It is intrinsic to GPS that this is the >case. You cannot get around this.
Actually I think the number is around 15 minutes from the time you get code data from the first satellite. (I have always wondered why the almanac isn't staggered between the satellites, that way you get get it at least four times faster on average). >Others are >cold only if they have been off so long that they have no way of >knowing the current correct leap count. Given that BIPM only >publishes 6 months in advance, this means that the longest a receiver >can be off is about 6 months. I think you risk confusing two things here. At least the Oncore receives will happily use a 2 year old alamanc to aid in getting first fix. But they will not use anything but the current almanac to report leap seconds. >Also, a GPS receiver that has cached the almanac can acquire >satellites much more quickly than one who has to wait for the almanac >to be downloaded. This is btw, the original design rationale for the almanac data set. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
