Safe Speed Forums

Not really - radio - well where I come from and in that day and age - you know as well as me how well AM copes with hills etc( even now FM-now you hear it ,now you don't) . So the radio was always ( even now ) a waste of time .Possibly -now I might have it set to Smooth Radio to get road reports ( just hit "ON" button ) ,ot have a CD with some bagpipe music ( to upset loud music idiot at lights) .Now having a ciggie - in my part of the world ,in my yoof -no radio -so you needed something -and the roads -nothing like Brum - more like some rally stage - gear lever in one hand ,wheel in other - so when one hand came free on a straight - fag time .Amazing just how other limbs came into play to get that nicotine fix .Multi tasking was a way of life -even more so in the diesel vans of that time

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lets bring sanity back to speed limits.
Drivers are like donkeys -they respond best to a carrot, not a stick .Road safety experts are like Asses - best kept covered up ,or sat on

Yes I always love a good laugh at some thing that is absurdly wrong. Altitude (n: Height of object, esp above sea level) does not vary with temperature and pressure. Otherwise turning on the radiator would cause you to levitate. 'Altitude sickness' is a terrible misnomer as you can suffer the effect of reduced pressure at any altitude, even sea level, in an hypo-baric chamber.


Not so. Your aneroid altimeter will change with pressure an thus give a false altitude reading. My GPS altimeter will, within the vagaries of the sattelites, show the same reading whatever the pressure.


Best do that. It is too weak to stand up. A generic altimeter does not measure atmospheric pressure.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

Phew, ta. Getting a bit heated elswhere though. I hope no-one falls out over it..


I’m not sure it isn’t hypocritical to say speed cameras and having to keep an eye your speedometer are a distraction but dealing with a blazing weed isn’t.

Even if it were legal, I wouldn’t want to be on a coach trip where the driver is smoking. I would want him or her to be concentrating on the road - not wondering where to douse the cigarette, light one up or looking where to flick the ashes.

Driving should be taken more seriously than that IMHO, especially in these busy days

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

Some real substance there dcb, well done, lol!

The fact of the matter remains, the Ordnance Survey use elevation to describe the height AMSL of points on the surface, as this is the correct terminology. The original issue involved the areas of aviation and aviation medicine, areas in which I have received some of the best training in the world, and know myself to be correct in this case. What is your area of expertise, and what level of expertise qualifies as an informed source in your opinion, or is agreeing with you the sole prerequisite beyond having a webpage?

Is it clearly not physics, or you'd be aware that warm air is less dense than cold, so you'd actually need to cool the air down (an awful lot!) before you'd be floating. Maybe your radiators do this, it wouldn't surprise me given your predisposition to be contrary, despite your ignorance. While absolute altitude may not vary with pressure or temperature, both pressure altitude and density altitude depend on at least one of these variables, and since we are talking about breathing the air, these are the ones that matter. Incidentally your GPS does not display altitude, as reference to MSL, it is height referenced to a spheroid datum that is often quite different from mean sea level, and would require augmentation to read a usefully accurate altitude.

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Regulation without education merely creates more criminals.

Not on my maps which specify "Surface heights are to the nearest meter above mean sea level. Heights shown close to a tiangulation pillarv refer to the ground level height at the pillar.


I have no doubt that you are well trained in aviation medicine and that is why you insist that altitude is a measure of pressure rather than of height. My area of expertise is Astronomical Instrumentation. In that field altitude refers to the angle of a celestial body above the local horizon and is measured in degrees. But I would not be so brash as to insist that my expertise entitles me to expect everyone else to accept my specialised use of the word. Nor should you.


At last, you have seen my point of view. If you had originally referred to 'pressure altitude' rather than just altitude I would have had no argument with you


No - it measures the position relative to the WGS84 geode. As that geode is well defined it is possible to convert the measurement to a height above MSL. But the calculation is complex, especially at low altitudes and the chipset in my cheap consumer unit cannot do it very well. As the errors vary with satellite geometry you cannot correct the instrument by taking a reading at a known altitude. A transmitter at the centre of the Earth would solve that problem but the technology for that is not yet in the public domain

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

A couple of points before the final thrust:



As the matter being discussed was quite clearly involving pressure altitude, as evidenced by the very fact that the oxygen analyzers (sic) read anything other than 21%, I did not feel the need to spell it out just in case I drew your pedantic wrath. Perhaps I should be more careful in future, but I doubt I will be, it's not me with the problem, and I quite enjoy this sort of thing!



Not globally, but the system can be, and in many applications is, augmented on a local level by reference to a ground-based station of known three-dimensional coordinates. Correcting for a known altitude will also improve the accuracy locally, for a period, in an area more than wide enough, and a timeframe more than long enough to make a GPS instrument approach, for example. There are also codes which will alow greater accuracy from the satelites alone, though these are not available to most!

Finally:



Nor do I! Astronomers can call altitude whatever they like, right here we were talking about aviation, as I'm sure you can agree, and the difficulties of breathing air at pressures significantly different from those experienced across most of the earth's surface, therefore the aviation definition would seem the most appropriate, wouldn't you say?

As for elevation, did you follow the links I was quickly able to find, or look for others? Elevation (meaning the height AMSL of a fixed point on the surface) is referred to in every OS publication that I just checked, about 50 different ones before I got seriously bored and felt justified in declaring a trend. These were not solely aviation products I should add (though some of course were). These included non-aviation 1:25000 and 1:50000 maps. Perhaps most importantly however, and really this is the crux of everything we have discussed, is that whether they use elevation or the synonymous height AMSL to describe a fixed point on the surface, they do not use altitude.

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Regulation without education merely creates more criminals.

That is unfair and I don't admit to being pedantic. In common parlance, altitude usually means the same as elevation. The concept of 'pressure altitude' is, presumably, something that is familiar in aviation medicine. But it is unreasonable to assume that laymen understand what it means even in that context. I deduce that a 'pressure altitude' of ,say 3000meters, means that the pressure is the same as it would be in free air at 3000m above sea level. Is that correct? And how is temperature taken into account? Is there such a thing as temperature altitude?. Those are serious questions. I enjoy this sort of thing, especially when I stand to learn from an expert.



I should have said "by taking a single reading at a know altitude" . I think that you are describing differential GPS, where the mobile station is continually updated from the fixed station. That works very well provided both stations see the same constellation of satellites. As for the SA codes - we would have to kill one another if we discussed that



Indeed it would. But only after you have told us that definition. As I stated above, if you use technical terms from your own area of expertise it is not fair on the layman to expect him to understand them without explanation. If I were describinag how a radio interferometer works I wouldn't expect you to understand what the terms such as correlate, convolve or even transform meant in that context.


I Googled "Ordnance Survey Elevation" and most of the hits use the term elevation in the architectural sense - as in "elevation profile" All of my Landranger and Explorer maps and our Definitive Rights of Way maps use the term height rather than elevation. But these are old maps and the word elevation may be creeping into modern usage. My wife, who is a copy editot and proof reader by profession, tells me that she would normally prefer height to elevation.



Point conceeded

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

Have a look at: http://ukvapers.com/

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I won't slave for beggar's pay,
likewise gold and jewels,
but I would slave to learn the way
to sink your ship of fools

I would put it to you that there are many words 'in common parlance' that relate to technical topics and are routinely used incorrectly. If my attention was brought to my genuine misuse of the word I would be glad to be able to avoid misuse of that word again in future, I would not argue the toss.

If we replace your "free air" with "the international standard atmosphere (ISA)" then you're pretty much there. Sea level pressure in ISA is 1013.2mb, and the pressure lapse rate is approximately 1mb per 30'. Tongue-in-cheek to an earlier point of yours, measuring altitude in metres is a very American thing . This is in contrast to your true altitude, which is referenced to actual sea level pressure of the day (well hour actually), and is very accurate given the relative constancy of the pressure lapse rate. PA is useless for terrain avoidance since all the elevation figures on the charts are referenced to actual mean sea level, so it is only used above a transition altitude, which is obviously higher in areas of higher terrain.

Density altitude is PA corrected for temperature difference from ISA, which is 15 degrees celsius at sea level with a lapse rate of approximately 2 degrees per thousand feet.



I believe that a single reading would be enough to increase accuracy for a finite period within a finite area, merely by giving a coarse correction vector. I was indeed describing DGPS, which can increase accuracy sufficiently to allow an 'ILS' approach to be flown to a non-ILS-equipped runway (or even field if you're a helicopter) and I understand is close to being licenced to do just that in the States.



I do not believe that to be the architectural sense, but the height AMSL sense. An elevation profile is a 'slice' through a particular bit of landscape, effectively a graph of the changing elevation along that route, which need not be a straight line. It would show you, for example, the ups-and-downs of a particular walking route, the same way as an altitude profile would show you the ups-and-downs of a particular flight. As the definition of elevation is the height AMSL of a point on the surface your OS maps are not necessarily incorrect in their use, merely incomplete, though I would contend that it is a completely justified omission since all the heights they list are on the surface and AMSL. As previously concluded, my original issue was with the use of altitude for this purpose.

A small request from me, not getting at you, but if you remove text from within a block of mine that you've quoted, could you please indicate so with elipses? Cheers!

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Regulation without education merely creates more criminals.

That's unusual Robin; they favour, (or should I say 'favor'), Imperial measurement as a rule.

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

My experience with engineers in the USA is that they wouldn't recognise a meter if it bit them on the arse.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

http://edition.cnn.com/TECH/space/9909/30/mars.metric.02/

It makes you worry......

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The world runs on oil, period. No other substance can compete when it comes to energy density, flexibility, ease of handling, ease of transportation. If oil didn’t exist we would have to invent it.”

56 years after it was decided it was needed, the Bedford Bypass is nearing completion. The last single carriageway length of it.We have the most photogenic mayor though, always being photographed doing nothing

Well, maybe not too much Jom..

The greatest commercial aircraft of all time was a joint venture between us and France.

They worked in metric while we worked in Imperial and it all went together quite well.

That which we call an inch by any other name is still 23.3995 mm

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

Now ,would that be ,Volt METER / Amp METER /Watt METER - or any other kind of measuring device .

A "METRE " IS A MEASUREMENT OF DISTANCE .

A "METER " IS AN INSTRUMENT USED TO MEASURE .......................


things like throws / etc come to mind - now , let's be accurate in terminology .My experience with engineers in Canada / USA in the 60's ( when TAT1 & CAN TAT were the only transatlantic forms of communication tells me that engineers in Canada /States DID know the difference)--4.5kv to me in the UK ,was also 4.5kv to those State side .

_________________
lets bring sanity back to speed limits.
Drivers are like donkeys -they respond best to a carrot, not a stick .Road safety experts are like Asses - best kept covered up ,or sat on

Collapse of stout party

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

I could insert a smug smilie here, but I'll resist

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

And I could point out the difference between, on my part, a typo; and ,on your part, using the - according to Steve - fallacious Appeal to Authority to deny the existence of a word . But it is lovely sunny evening so I won't.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

But 'ang on a mo...

How do we know yours was a typo? Na na na na na

I'm sure it was a typo but can't you just for once in your life not be right!

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

I was wrong once. I thought that I had made a mistake but it turned out that I hadn't.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

Can I meter that response ( or measure it using a tape measure calibrated in METRES)

_________________
lets bring sanity back to speed limits.
Drivers are like donkeys -they respond best to a carrot, not a stick .Road safety experts are like Asses - best kept covered up ,or sat on