GPS or odometer?

[PedalUma]

I like to install a compass in the kid's area of cargo bikes. I am working on one now. I also sometimes put a little propeller airplane and always a bell there. When I was in Whitehorse, Yukon I felt ill because of the almost straight down magnetism. I think that I am more sensitive than most. My first night in NZ they aske me to point North. I pointed South. Here in Nor Cal declination is between 15 and 20 degrees. Many property lines and roads and off by that much. So, North on a road is really NNE.

 

[dodgeman]

I am a retired land surveyor and have studied how they laid out the sections of ground, the one mile square parcels of ground, in Illinois. They used a compass for a lot of it and tried to take the declination into account. They used a compass in Illinois along with a chain 33 feet long. By todays standard the accuracy was pretty weak , often with an error of 1 foot for every 100 feet they measured, sometimes worse. Generally there was pretty consistent except where there were areas of a local magnetic attraction, like in the northwest part of Illinois near Galena. They had no way of knowing everything was out of whack as they measured.

 

[PedalUma]

@dodgeman, Could a one square mile piece of land have more than one mile of surface, if there is a mountain in the middle of the property?

 

[mschwett]

while we are on the subject of compasses… for those in non-equatorial regions, are they for people who don’t know, for some reason, where the sun is? or solely for navigating at night? i must be missing something, because the giant ball in the sky - and the shadows it casts - follows a very, very predictable pattern

 

[Mr. Coffee]

while we are on the subject of compasses… for those in non-equatorial regions, are they for people who don’t know, for some reason, where the sun is? or solely for navigating at night? i must be missing something, because the giant ball in the sky - and the shadows it casts - follows a very, very predictable pattern

Try to walk a precise bearing over complicated terrain in cloudy or foggy weather (or at night) and get back to me about that.

Try to get a decent position fix by sighting and getting bearings on known objects using just the sun and shadows.

 

[mschwett]

Try to walk a precise bearing over complicated terrain in cloudy or foggy weather (or at night) and get back to me about that.

Try to get a decent position fix by sighting and getting bearings on known objects using just the sun and shadows.

i see, so it’s also a precision thing. i’ve never navigated that way on uncharted routes, it’s always been relative to paths or trials or roads, and as long the sun is up, it’s pretty easy to know which way is which.

on the other hand, a young woman was lost and asked me for directions recently and i said “west” as part of the directions. she said which way is that. i pointed and said towards the ocean and the sun (6pm in san francisco) she said “which one?” so i said “which ocean or which sun?!?” and she said “sun i’m not from here.” FIRST CONTACT !

at this point i changed the wayfinding strategy i was suggesting

 

[Mr. Coffee]

i see, so it’s also a precision thing. i’ve never navigated that way on uncharted routes, it’s always been relative to paths or trials or roads, and as long the sun is up, it’s pretty easy to know which way is which.

Well, yeah. No compass is necessary in situations like that.

But if you are in terrain with no reference points, confusing reference points, or you can't see any reference points, you'll probably want a compass or the equivalent and have a clue about using it.

One pretty alarming no $#!+ story I have is about being hopelessly lost and disoriented within earshot of a busy highway. I know it sounds stupid but it was in very heavy forest and even though I could hear the vehicles I couldn't really figure out which direction they were, plus the fact that I was soaking wet and tired and hungry and had very little patience made it kind of a tough afternoon. Also because of the dense jungle walking in a straight line for even short distances was impossible.

People shouldn't think that with GPS it is impossible to get all messed up. It still is. For one thing, GPS accuracy can go wildly wrong in certain terrain (dense forest and deep canyons come to mind). For another, if you are using reference information sometimes that reference information uses different coordinate systems than you'd expect. Having GPS coordinates relative to an unexpected datum or with a different geode can be a sure fire way to see some unexpected country.

on the other hand, a young woman was lost and asked me for directions recently and i said “west” as part of the directions. she said which way is that. i pointed and said towards the ocean and the sun (6pm in san francisco) she said “which one?” so i said “which ocean or which sun?!?” and she said “sun i’m not from here.” FIRST CONTACT !

at this point i changed the wayfinding strategy i was suggesting

Some people you just can't help.

I've taught some orienteering classes and have seen people use the wrong end of the compass needle. It is also very possible to get the polarity on declination wrong.

 

[dodgeman]

@dodgeman, Could a one square mile piece of land have more than one mile of surface, if there is a mountain in the middle of the property?

View attachment 159330

Yes it could. When it comes to boundary surveying 99.9% of the time the distances are horizontal, in other words assuming the world is flat. In most cases I think the amount of extra land wouldn’t be that much but in the mountains or in steep terrain it could be significant.

 

[dodgeman]

That's 99% accurate.
I'm good with anything over 80%.

That was the standard of the day. It’s pretty poor by todays standards. I can do better with a cloth tape and a plumb bob. If you measure to 80% accuracy as a carpenter your going to throw out a lot of lumber.

Yes, I’ve gotten lost in the woods surveying. It’s easy to do and a compass is pretty valuable.

The GPS we used that was survey grade accuracy was very expensive, our last system was $60,000 and no it doesn’t work in heavy tree cover. There are all sorts of coordinate systems, geoid models, metric system, US survey foot, international foot but once you learn them and how to go from one system to another, it’s not bad but there is room for screw ups. For example Illinois is going from the US survey foot to the international foot. Without getting into details they are the same except when converting from the metric system. In that case it makes a difference.

 

[mschwett]

Yes it could. When it comes to boundary surveying 99.9% of the time the distances are horizontal, in other words assuming the world is flat. In most cases I think the amount of extra land wouldn’t be that much but in the mountains or in steep terrain it could be significant.

really? the large scale surveys i work with always reference the navd ellipsoid or newer geoid. vertical dimensions would be noticeably off if the surveyors assumed the world was flat, no? the curvature of the earth is around 8 inches per mile.

 

[Mr. Coffee]

the curvature of the earth is around 8 inches per mile.

That is on the order of 0.01 percent.

 

[peterh_nz]

If anything got to the fence, sirens went off and the Bombers were sent to Russia to drop their nuclear bombs.

Really?

 

[dodgeman]

really? the large scale surveys i work with always reference the navd ellipsoid or newer geoid. vertical dimensions would be noticeably off if the surveyors assumed the world was flat, no? the curvature of the earth is around 8 inches per mile.

The hand held data collectors or the instruments we use correct for earth curvature. The gps we use has different coordinate systems loaded in it. Almost all the gps work we did was working is in state plane coordinates. The software in the data collector and drafting software took care of a lot of the geodesy and took a lot of the calculations out of it. If you’re doing old school and using a 100 feet steel tape you use a plumb bob to correct your tape to horizontal. If you’re taping 100 feet at a time you are essentially following the curve of the earth so no need to worry.

There are a lot of reasons boundary surveys are corrected to horizontal, for example if the terrain changes the distances would change.

 

[Stefan Mikes]

I don't know guys how you feel about it yourselves but I just love to see my riding direction (such as Heading: SE) on my Wahoo on long rides, especially when it is the area not familiar to me, and I know the wind direction.

Mark you may laugh as much as you want but some world areas outside So-Cal may have the sky cast with clouds!

 

[PedalUma]

I can get turned around in fog. It is easy to drift 2 degrees per minute. Pretty soon you are off by 45.