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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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 Posted: Thu Feb 10, 2005 11:07 pm Post subject: Re: on a slope ? |
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| digga wrote: | | hey I had never even thought as to if i would be as accurate on a slope as on the level ? |
Ahh, I never thought of that either. 8O
GPS measures distance in two dimensions (lattitude and longitude) so if you measure the distance from point A to point B and one point was a different elevation to the other then the distance indicated by the GPS would be shorter than the actual distance you traveled to get there.
The error wouldn't be very much though. A 1 in 5 gradient would give a 4% under reading.
The GPS does measure your height too, but I don't think it takes this it into account when calculating the distance. I don't think the error is enough to be worrying that much about. Maybe you could just charge a bit more for hilly ground. 
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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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| Posted: Fri Feb 11, 2005 1:57 am Post subject: Re: on a slope ? |
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| digga wrote: | | You can then print off the map with the overlaid track log and waypoints for a very professional looking result as i will need a print out of the measurements to show the client any suggestions on software to do this: D |
OK, a quick start for you:
1. Get an OS map to play with Right click on the map and select "Save As". You will have to open it in paint (or something) to convert it from a GIF to a BMP for use in Ozi Explorer.
2. Get a trial version of Ozi Explorer
3. In Ozi Explorer, select File -> Configuration -> Maps and set the "Alternate Grid" to BNG and select your preferred units (feet/meters etc). Also select your GPS type (if any).
4. Now select File -> "Load and Calibrate Map Image" and load the bitmap image.
Ozi Explorer has no way of knowing the lattitude and longitude of your image so you have to calibrate it. If you click on a part of the image in Multimap then it will tell you the lattitude and longitude of that point. You can enter two points (at opposite corners) into Ozi and this will calibrate the image.
You should now be able to go to the Garmin menu and tell it to download the tracks and waypoints from the GPS unit and overlay them onto your map. With a bit of luck, it might work, it's a lot of messing around though.
You might want to have a look at the other topographical mapping software available (read the reviews here), some of which come with OS maps included and already calibrated for you.
If you don't already know about the British National Grid then have a read of this tutorial
There is an awful lot more to learn and that's about the limit of my knowledge. Hopefully this is enough of a pointer to kick start you in the right direction - you will have to figure the rest out yourself!!! 8O
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digga
Occasional Visitor
Joined: Feb 05, 2005
Posts: 7
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| Posted: Mon Feb 14, 2005 7:26 pm Post subject: on a slope |
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Hi am I right in thinking the steeper the slope the further out the measurement would be ?  |
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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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| Posted: Tue Feb 15, 2005 1:45 am Post subject: Re: on a slope |
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| digga wrote: | | Hi am I right in thinking the steeper the slope the further out the measurement would be ? |
Yep, exactly right. Take the square root of the square of the distance travelled plus the square of the difference in altitude. 8O
ie, your GPS says you walked 100 meters and climbed 20 meters, so the actual distance is the square root of (100 * 100) + (20 * 20) = 102 meters
| Some bloke called Pythagoras wrote: | | For a right angled triangle the square on the hypotenuse is equal to the sum of the squares on the other two sides. |
Now write that out 100 times. 
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digga
Occasional Visitor
Joined: Feb 05, 2005
Posts: 7
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| Posted: Sun Feb 20, 2005 3:34 pm Post subject: thanks |
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| hi thanks for all the help and info u have given me still havent desided what gps setup to buy but if i need anymore help i will know where to come :D thanks again |
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