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Unfortunately the devices don't appear to be made for people who want to log all possible information, every second and for 10 hours a day. I think I'll be transferring the data to a laptop at the end of every day, I can't see how else I'd be able to store the information on it for week straight.
I've been thinking about calculating the distances between points, mostly about how pedantic I should be with the Earth's spheroid rather than spherical shape and also the fact that a^2 + b^2 = c^2 doesn't apply on a spherical surface. Those can be solved, but the thing I'm not sure about is Wikipedia says that "Parallels are each 110.9 kilometres away". Are they actually defined so that they are an equal distance apart meaning one degree of latitude could be a different size to another, or is the angle correct and the distance between parallels will vary by a tiny amount?
I've been thinking about calculating the distances between points, mostly about how pedantic I should be with the Earth's spheroid rather than spherical shape and also the fact that a^2 + b^2 = c^2 doesn't apply on a spherical surface.
Um, I think over the kinds of distances you're going to ski, the curvature of the earth is hardly important Especially when you factor in the bumpyness of terrain in ski resorts which is going to cause you far more problems than the curvature of the earth ever will. I'd just assume that the earth is flat.
Don't forget to factor in the change in altitude as well as position between any two points. This will mean the points are further apart than if they were on the same plane and thus your speed or distance calculations could be out by several percent (not insignificant). Again, calculating distances between two coordinates on the WGS84 datum is FAR from trivial. I suggest using a library of some sort as many people have spent months solving that problem.
I think the lines of latitude are fixed distances. It's the lines of longitude that are defined as an angle east or west of the Greenwich meridian and are therefore different distances apart depending on how far north/south you are (biggest at the equator).
Why not start out by plotting your data using Google Maps or Google Earth? That way, most of the hard work is done for you and you can view it in 3D with real terrain info.
I know that the curvature of the Earth isn't important for 1 second intervals, but I'd like certain parts of the program to work for data sets which might have large distances between points. As for the change in altitude affecting the distance between two points, I've got that one covered. I was also thinking about using the SRTM data if the program is supplied with a data set that doesn't include altitude. I think I'll need to get the Q1000P sent to Australia from somewhere, I expect I'll just charge it from USB so I'm not particularly worried about getting a charger that runs on 110V.
Well most modern chargers don't use transformers but use triacs instead, so if they work on 240V then they should also work fine on 110V. If you like, I can check the specs of the charger I was supplied when I get home.
Are there no suppliers on eBay that ship the Q1000P to Aus?
Joined: Dec 28, 2005 Posts: 2003 Location: Antrobus, Cheshire
Posted: Thu Mar 06, 2008 11:24 am Post subject:
mfrebuilt wrote:
I've been thinking about calculating the distances between points, mostly about how pedantic I should be with the Earth's spheroid rather than spherical shape and also the fact that a^2 + b^2 = c^2 doesn't apply on a spherical surface. Those can be solved, but the thing I'm not sure about is Wikipedia says that "Parallels are each 110.9 kilometres away". Are they actually defined so that they are an equal distance apart meaning one degree of latitude could be a different size to another, or is the angle correct and the distance between parallels will vary by a tiny amount?
Because the earth is an oblate spheroid (approx) with slight flattening at the poles, the distance between parallels change slightly at the higher latitudes.
For areas between +60 and -60 deg (NS) each minute, i.e. 1/60 of a degree, is a nautical mile.
You should be able to find s/w libraries on the web to convert WGS84 locations to UTM - which allows you to do simple distance calculations between points that are within a small area of the earth. It's like using OSGB in UK - you can do simple Pythagorean maths and get accurate result over a mile or so. But as already mentioned - it's the inclines that are going to mess it up. A 45 deg slope (probably not that uncommon on hillsides) will render distances approx 40% too short and hence give incorrectly high velocities etc. If your GPS has a barometeric altimeter and it logs it, you could determine the difference in altitude fairly accurately over a short time-frame. Unfortunately GPS derived altitude varies too rapidly to be accurately used. _________________ Phil
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Especially when you factor in the bumpyness of terrain in ski resorts which is going to cause you far more problems than the curvature of the earth ever will. I'd just assume that the earth is flat.
