qwazix | # 11 | 2013-03-25, 11:05 | Report

There was an app for that on the i8910 too which downloaded some data valid for a week. After that, fix was instant. Maybe sniffing that would be a good idea, but I don't have the i8910 anymore.

regulus | # 12 | 2013-03-25, 11:17 | Report

So the root of the cause is just the initial download then (thus, as a rule of thumb, one should use their home/office wifi before leaving the base, then they can switch to GPS only), and it's like that on all related gadgets?

Or can your gadget also get out of sync somewhere along the way, after hundreds of miles, even on a clear day with no visible obstructions between the satellites and the gadget? How long do the downloaded ephemeris and almanac hold before the gadget deems them out of date?

EDIT: Never mind, seems it's 30 minutes:
http://gpsinformation.net/main/almanac.txt
"[...] Almanac data is not very precise and is considered valid for up to several months."
"EACH SV broadcasts ONLY its own Ephemeris data. This data is only considered valid for about 30 minutes. The Ephemeris data is broadcast by each SV every 30 seconds."

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Last edited by regulus; 2013-03-25 at 12:57.

Wikiwide | # 13 | 2013-03-25, 13:13 | Report

Quick reply...
Considering that trimble's orbital information seems to be the same for any place on Earth, hundreds of miles shouldn't matter.
As they say, ephemeris data should be considered good for up to 30 days (maximum); if you are attempting to predict GPS conditions for weeks into the future it is recommended that you repeat your predictions a week (or two) before collection to verify the results (satellite conditions are constantly changing).
Just reading about GPS and GPS signals on Wikipedia; hearing from satellite once is enough to know its orbit precisely, but in order to get approximate orbits of all satellites (almanac), it has to receive twenty five frames, half-a-minute each. Therefore, storing this almanac on the device, and updating (about once a week) it when there is a faster-than-satellite connection would be neat.
The main problem would be wrangling the data into helping the GPS receiver. I still don't understand what kind of software should be installed on a server to make it an A-GPS server, to somehow allow the GPS receiver to understand that it doesn't have to load anew the almanac from the satellite.
Best wishes.
_________________
Per aspera ad astra...

don_falcone | # 14 | 2013-03-25, 14:07 | Report

Get an external BT SiRF III (or newer)-based mouse, problem solved. Even works in canyons or Manhattan.

pichlo | # 15 | 2013-03-25, 17:32 | Report

In 2010, I bought a second hand Tom Tom made in 2006. It had never been updated until I purchased new maps before a trip to Austria in 2012. I have also never updated it since that trip. Yet never have I noticed GPS lock times anywhere near to comparable to my N900.

I believe the trick is to store the last known position before switching off the device. The next time you fire it up again, chances are you are at or close to the same location. Indeed, once I got off the plane in Salzburg, my Tom Tom took about 10 minutes to lock but on the way back, I kept playing with it on the plane to see where we were and how fast we were flying and hey presto - I got an instant lock when we got off at Stansted.

I don't believe it would be such an insurmountable task to implement something like that on the N900. It seems to me that it always starts from scratch which seems rather inefficient.

That would work but means carrying two devices, worrying about another battery running out etc.

skanky | # 16 | 2013-03-26, 10:33 | Report

Do people find they need to regularly clear the gps cache, as per the bug report (I could find the link if necessary, but it looked to be well known)? If so, it could be that the n900 should remember where it was, but is not doing it correctly?

don_falcone | # 17 | 2013-03-26, 10:56 | Report

The N900's will run dry long before the mouse's, which btw come often with replaceable batteries. My Royaltek one even is Nokia battery compatible. Also, at the size of a typical mouse, complaining about having to handle two devices seems.

Face the facts: a N900 is a typical jack of all trades but master of none. If you want good & reliable GPS / navigation performance, use something else.

pichlo | # 18 | 2013-03-26, 11:32 | Report

Which is why I am not going to get rid of my now 7 years old Tom Tom just yet

skanky | # 19 | 2013-03-26, 11:39 | Report

Seems to be discontinued. Anyone able to recommend a newer one?

don_falcone | # 20 | 2013-03-26, 18:01 | Report

I haven't follow'd up technology as i'm still very happy with my RoyalTek RBT-2110. And now anyone tell me that this device is too large to bring along!