surveying tool for measuring heights of buildings etc?

[Bruce]

On the contrary, I have all the evidence that I will ever need - otherwise I would not have made the statement in the first place.

And I have no need to admit that I'm wrong, unlike you.

[Roger]

The message from Bruce contains these words:

It may be that the GPS Chris has has an averaging facility and if it has then it will average the gps altitude, not the barometric altitude. Hardly likely if the vertical accuracy was really as bad as Bruce makes it out to be.

[chris French]

It may surprise you to know that the information available on the Internet extends to rather more than GPS manufacturers marketing information.

Umm, yes, that was one of the reasons for choosing the model I did, but there is a difference between saying that consumer GPS units aren't very good at determining altitude and saying that the altitude inaccuracy can be an order of magnitude more than the horizontal accuracy.

ISTR from my reading around that an accuracy of 1.5 -3 X horizontal accuracy is likely

[Andy Champ]

We, on the other hand, have no evidence whatsoever that you are correct.

I can assert that because the satellites are up in the sky the vertical resolution is better. By saying that I am giving a statement of opinion backed up by a theory - which would be shot apart shortly, if I were not acting as a devil's advocate.

You have given a statement of opinion backed up by no theory whatsoever. I would be crazy to give your opinion much weight.

I have in fact been unable to find any reference that states that accuracy *with SA disabled* is any different in any particular axis - which is what I would actually expect, as the satellites are arranged in a rough sphere.

Andy

[Andy Dingley]

If I had the time to argue with the wilfully obtuse, I wouldn't have bothered killfiling Steve Firth. GPS altitude accuracy sucks, the rest is a trivial piece of research, so get your own finger out.

[Roger]

The message from Bruce contains these words:

Faith in your own infallibility is not evidence.

There is only one way you will ever convince me that I am wrong (and indeed anyone else apart from Dennis and maybe Dribble) is by producing your evidence.

So you say but I don't believe you and I doubt very much if your coy attitude is impressing the natives lurking on the sidelines.

I am always ready to admit I am wrong (if I am) but I need some convincing. And your posturing has been extremely unconvincing to date.

[george (dicegeorge)]

much simpler than catapaulting up the sardine then the cat then shooting the cat and timing its descent.

thanks

John Rumm wrote:

[Roger]

The message from Andy Champ contains these words:

It is there though. Just nothing to suggest that we should expect the vertical accuracy to be 10 times worse than horizontal accuracy.

for one which contains the interesting information that vertical accuracy depends to some extent on latitude and the accuracy decays markedly in the higher latitudes (above

65 degrees). However no suggestion of how bad it gets.

[Mike]

My more than five year old Garmin has been within a couple of metres of the published height when I placed it on selection of trig / surveying points.

[Andy Champ]

Excellent page, thanks.

He's seeing vertical nearly half as accurate as horizontal. Certainly not an order of magnitude!

Andy.

[george (dicegeorge)]

but the ground is sloping unevenly.

But it came to me today whilst driving my car- if i get a vertical bit of card and 2 tubes pivoting on the card, then look through the tubes and adjust the angle between them until I can see the bottom through one, and the window I want to measure the height of through the other, mark the angle, then turn it horizontal and sight from the corner of the house and remember where the other tube points to along the bottom of the wall then i can measure from that point to the corner with a tape measure and that will be the vertical distance near enough if the ground isnt very slopey... if my reasoning is correct!

[g]