Saturday, June 28, 2003

Weekend fun time !

The weathers sh1t but there's always something entertaining on the web !

Best laugh today was watching 'Pink Five' on Atomfilms Starwars fan film collection. See again the attack on the deathstar from the cockpit of a rooky pilot who is more worried about helmet hair than protecting her wing man. Porkin's choice is also very good - seems we should not expect the selection of channels on TV to be any better even in 'a galaxy far, far away'

LED's - are they the future of lighting ?

I thought so - and the not-quite-ready-for-consumers OLEDs may change it - but my experience says no. I got some not-cheap LED clusters rigged as replacement for 12v bayonet type bulbs. Sold as just as bright and cool running and many less amps. So far I have got no more than a modest glow from them. And this site explains that they are not really much more efficient when true like4like comparisons are made.

I have e'd the suppliers for suggestions as to why I am not dazzled - lets see what happens.

Friday, June 27, 2003

GPS time vs. UTC or Civil Time Is there a problem here ?

On BBC world this morning they were saying there is a potential problem because GPS time is not updated with leap seconds in the same way that UTC time is updated about once a year, so that GPS time is now different by 13 seconds. But I checked a couple of GPS units against a radio time standard and could not see any 13 second difference.


This US Navy link explains the many different time standards and their history and also mentions the 13 seconds but also says GPS time is synchronised to UTC - so which is it ?

I think the answer is that the GPS system sends packets called NAV in with the other packets types and in the NAV packet it says how many seconds to correct GPS time by to get UTC, so the users GPS unit uses this to show the user UTC - not GPS time. For the differences of less than a second the US Navy 'steers' the GPS time daily to keep the remaining error to less than a microsecond.

So it seems - yes there is a 13 second difference - but systems already correct for it so we don't see GPS time - even on our GPS units. Like the watch I am wearing !
illustrates the different times, but note it uses your system clock as a base - it does not look for a real time standard.

A quote from Garmin expalins why their units and any other GPS unit may show the 13 second error when first switched on - because the NAV signal with the correction is only transmitted every 12 minutes - so it may be that long before the unit hears what correction to apply. Also THe comment on 1-2 second errors in the displayed time is attributed to the task scheduling in the users unit, display is a lower priority than calculating - so the units clock is very accurate but the software takes some time to display that on the screen.

So now we know - a little more than before

Tuesday, June 24, 2003

I was looking for something else but found this on polar wobble
which is interesting in the variability it shows and the wide range of causes suggested for it. But what I was looking for was about the datum used for our Lat/Long coordinate system. Yes it is the Greenwich meridian - a brass strip in the ground in east of London. But I read how GPS measurements show all of UK drifting NE several cm a year ! And so Greenwich moves, but does the meridiwn move with it ? I found this old entry saying that an average of many datums world wide is used in WGS84 to compensate for tectonic movements.

Monday, June 23, 2003

I saw Orange Roughy on menu and I wondered :-

Should we eat Orange Roughy ? Can this strange fish caught only at extreme depths 700m - 1300 m deep off New Zealand and Namibia be harvested sustainably ?

Seems no one really knows - but catch qty's fell fast after commercial fishing started - and the excuse that the fish had become smart about avoiding the trawls does not work ! If they live for 100+years abd take 20 years to become mature to reproduce the yield is very low and they could be caught to extinction very easily.

Some sites about this are
Orange Roughy Management

Came across a 'new' bike design at
Interesting ideas, don't know what it would really be like to ride lieing so flat - is balance different ?

But $3000 seems expensive to me .

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