Differences Between WGS & NAD Map Datum~How They Effect Maps

[maxpowers]

holy moly, I finally got my own thread just like i always wanted!

wow, that title is a bit misleading though... or is that what we were talking about?
sorry for causing such a disturbance.
peace.

[FalcoColumbarius]

Max, it's all about you (grins), you started this......

Seriously 'though; this is a good topic, like most of these "my pants are on fire" topics. Not only are they entertaining but one can learn a lot from them. Besides, I should have paid closer attention to my grammar and content in the first place.

Do you go offroading with a globe? or a local map?
over the distances on a local map, it's irrelevant.

I go off roading with a globe but supplement it with local maps. My globe is in the form of a three dimensional WGS84 GPS format and wrapped around that globe is a detailed ordinance survey map of Canada. I can plot a course to Delicat's folks' place in Quebec and take in a little Baffin Island along the way if I want to (and had the disposable cash for the transport of the MLB). The supplements are in the way of the Mussio Ventures Back Road Books, also in WGS84 (for compatibility). The reason I use this globe is not just for determining my azimuth, but for my altitude, too. I could use the NAD27 map, break out my pencil, string and transit compass and draw intersecting lines to determine my position and trust the elevation written on said map..... or ~ I could just look over my shoulder and see everything there. This would include being able to compare my GPS elevation with the ordinance survey line on the map ~ and..... compare my GPS elevation with my barometric altimeter and get a sense of the incoming weather and whether it is advisable or not to ford that three foot deep stream if there is no other way out.

When and why GPS was made is irrelevant to the discussion 1 . GPS again has NO information about land masses, rivers, roads, or any other feature, only your location on this planet 2 . as for "they made new maps"... who is "they"? 3 every map is made by a different company, and most use data much newer than 1984... and surprisingly (for you) 4 many still put that NEW data on a NAD27 datum... because the DATUM is UNRELATED to the DATA 5 . Each cartographer does things differently, the DATA is not "public domain" and there is no magic 1984 view of the world with all the features on it that is being used here.6
Just the SHAPE of the globe.

you MUST use the same datum that your map uses, no matter what 7. And disregarding a perfect map because you don't like the datum would be a very silly move indeed!

Many maps are still published in NAD27, I'm not going to avoid them to get a WGS84 map that is WORSE! 8

The DATA is serperate from the DATUM, 9 you just don't seem to understand that the 2 are completely, 100% unrelated.

Think of the datum as a piece of paper, if I use a 1927 piece of paper, or a 1984 piece of paper has no bearing whatsoever on the map I draw on it with my pen 10 . the paper is blank until the cratographer draws on it

• [1] Actually, it was made relevant to the discussion prior to Max pointing out the error of my grammar in a paragraph in the first post I made answering Ursula's question regarding advice for going off road. It is pretty much the "raison d'être" of this thread.
  
  [2] Well, yes and no. The global location on this planet happens to involve land masses, rivers, roads & other features.
  
  [3] "They" is all them other guys that formed those companies you go on about after you asked this question in the first place (twice removed from the original eighth place )
  
  [4] I know. I am not surprised. It seems that measuring the longitudinal co-ordinates from my mate's NAD83 GPS dropped me sixty odd minutes west into the Pacific Ocean on my WGS84 oriented GPS. Somewhat disturbing at around midnight in the bush somewhere. I briefly mentioned this a few posts back.
  
  [5] Oh, I know, mate. I made a grammatical error and a descriptive omission in the original paragraph that started all this. It was pointed out by Max, bless his heart, and, amongst other things, I answered back with "...originally based on 1984 data* (not to be confused with Map Datum). ...". Remember? You quoted that. I understand that the Datum is the "type" of Chassis or platform the map is built on and not the Data that makes up the picture that is the map. I have never disagreed with you on that point.
  
  [6] You are referring back to your comment regarding my comment about the origins of GPS in the public domain. Before Korean Air Lines flight 007 was shot down in '83 GPS was a military thing, only. After that incident President Reagan announced that GPS would be available to "civilians". As of 17 January, 1994 there were 24 satellites in the sky telling us where to go. Now there are 31. My reference to the maps is with the advent of WGS84 (also NAD83UTM -Max mentioned) as a different building platform ~ they, you know... them, the cartographers that be ~ had to build new maps to fit the new building platforms that is the new Map Datum. Otherwise people would be driving off cliffs into the Pacific Ocean instead of just getting lost down some deactivated logging road. Which really brings us back to the beginning of this ordeal: Like the Internet, GPS maps are not updated by one group of people. It is updated potentially by everyone who report where something has changed and the cartographers; Mr. Garmin; Mr. Tomtom; Mr. Magellan; et al ~ enter these changes into the respective maps. Some parts of the world have eluded the public eye and when driving in remote areas you must beware as you might just find that one of these forest mains is grown over with fallen trees and rotten bridges and sinking causeways, &c..
  
  [7] Agreed.
  
  [8] Fair enough.
  
  [9] Agreed, we covered that back on [5]. I might add 'though, that the Map Datum will determine the way in which the map is drawn, of course.
  
  [10] Well, on the 1927 piece of paper you will be using a two dimensional series pen and on the 1984 piece of paper you will be using a three dimensional series pen (w/digital harmonic capabilities). On the 1927 piece of paper you will be calculating from Meades Ranch in Kansas, on the 1984 piece of paper you will be calculating from the centre of the Earth to as high as the heavens above ~ in a three dimensional walnut shell.

Falco.

[Green1]

[2] Well, yes and no. The global location on this planet happens to involve land masses, rivers, roads & other features.

NO, IT MOST CERTAINLY DOES NOT!!!!!!!!!!!

WHAT PART OF THERE IS NO DATA IN THE DATUM DO YOU NOT UNDERSTAND???????????????????????????

Your WGS84 datum is USELESS without DATA on it. Data that can just as easily be plotted on ANY other datum!

Just because 1 map maker used WGS84 doesn't make it any better or worse than any other datum
NAD27 is capable of being jsut as accurate.

the WGS84 paper is flat for all intents and purposes when showing an area the size you are working with, the difference for this purpose is NOTHING

If you refuse to see the difference between DATA and DATUM you will NEVER be able to navigate properly!

In addition to this, MOST topographic maps in Canada are NAD27, meaning that if you insist on using any other datum, you will have to either convert, or simply not have the best data available.
Likely much of your "WGS84" maps have simply been converted from NAD27... I'd rather the original myself...

[Firesong]

I get a kick out of this.

Maps are made by companies, government etc.
Maps for GPS's are made by the same companies etc.

I've used my GPS with tons of different sets of maps.
Like any sane person, look outside the window, keep a map
of the area handy, extra batteries and your gps.

If your too stupid to be safe and use these things then
darwin will deal with you.

No big deal.
And they are pretty accurate. One of my pasttimes is
searching for stupid little thimble sized containers that
contain a piece of paper. The larger containers are
more fun though.

FS

[FalcoColumbarius]

Firesong, you were mentioning about the accuracy of GPS these days ~

When I first loaded up my Garmin/Nroute system I decided to go for a drive. I plotted a course up the Fraser Canyon with a stop over at this cool coffee place in Hope called "The Blue Moose" (you'd probably like this place). When I got to the cafe there was no parking immediately in front of it so I parked across the street, no big deal, right? Had my coffee, got back in my wagon and proceeded up the Number 1. As I am driving up the road my GPS keeps telling me that I have to turn around because I have yet to arrive at the Blue Moose ~ because I parked across the street and walked the rest of the way ~ my van never made it to the Blue Moose. This was trippy. GPS can be a great pastime, still learning.

Falco.

[Green1]

Firesong, you were mentioning about the accuracy of GPS these days ~

When I first loaded up my Garmin/Nroute system I decided to go for a drive. I plotted a course up the Fraser Canyon with a stop over at this cool coffee place in Hope called "The Blue Moose" (you'd probably like this place). When I got to the cafe there was no parking immediately in front of it so I parked across the street, no big deal, right? Had my coffee, got back in my wagon and proceeded up the Number 1. As I am driving up the road my GPS keeps telling me that I have to turn around because I have yet to arrive at the Blue Moose ~ because I parked across the street and walked the rest of the way ~ my van never made it to the Blue Moose. This was trippy. GPS can be a great pastime, still learning.

Most modern automotive GPS units can tell you what lane you are driving in on a multi-lane roadway, and GPS can be accurate to within less than a metre, your problem wasn't that the GPS was too accurate, it was that the programmer wasn't forgiving enough. A good programmer will set it up such that you "arrive" when you are within a hundred metres or so, and failing that, will set it so that it shows as visited once you proceed deliberately past the location.
I find some are better than others at this, I found that Microsoft Streets and Trips was horrid at this, my TomTom is hit or miss, and my old garmin was pretty good.

[FalcoColumbarius]

Most modern automotive GPS units can tell you what lane you are driving in on a multi-lane roadway, and GPS can be accurate to within less than a metre, your problem wasn't that the GPS was too accurate, it was that the programmer wasn't forgiving enough. A good programmer will set it up such that you "arrive" when you are within a hundred metres or so, and failing that, will set it so that it shows as visited once you proceed deliberately past the location.
I find some are better than others at this, I found that Microsoft Streets and Trips was horrid at this, my TomTom is hit or miss, and my old garmin was pretty good.

Yeah, mine more often than not will have the arrow pointing in the right direction after I have made a number of position changes, like backing and forwarding the van around in a car park. I am aware that it is the programmer, garbage in garbage out, right? I have used Microsoft and I have to agreed that it is terrible. Now I have Garmin PC Mobile as a platform but I am unaware that one could programme the accuracy of any given destination. Where would I find this feature in the menu?

Falco.

[Green1]

I am unaware that one could programme the accuracy of any given destination. Where would I find this feature in the menu?

Most likely, you can't... (though I could be wrong, I've seen that sort of thing in some software, it's just very uncommon) the person who originally programmed the software decided this one for you. Unfortunately for you, they chose a more precise definition of "arrived" than you have. I know my old garmin II+ chose to mark a location as visited once you stopped getting closer and started getting further away, regardless of distance, my TomTom seems to vary it's definition based on... well... I have no idea... I just know that sometimes it realizes I got there, and other times it spends the next hour or 2 telling me to turn around... Streets and trips seemed to want me to drive right in to the living room... it also refused to recalculate any route without manual intervention, so if you missed it, instead of telling you how to get back there it would simply tell you you're off-route... it was about the worst navigation solution I've tried yet. (though in fairness, it was 5 years ago, they may have improved since then)

[marsgal42]

Laura...your Delica is lifted REALLY high to have a view out the windshiled like that!!!

Great view out front (except when you're climbing and can't see over the nose), but the view out back is nil, and you have that great big blind spot under you. Checking that blind spot gives you an excuse to turn and bank like you're flying a Spitfire...

220 km/h and no brakes makes things interesting too.

...laura who drives Gumdrop to the airport

[FalcoColumbarius]

<-------- Spitfire (MkIX)The main difference between an L300 Delica and a Spitfire is the engine: The Delica engine is 2,500cc; the Spitfire engine is 2,500hp.

Most likely, you can't... (though I could be wrong, I've seen that sort of thing in some software, it's just very uncommon) the person who originally programmed the software decided this one for you. Unfortunately for you, they chose a more precise definition of "arrived" than you have.

Generally I have overcome this problem by going off course to the coffee shop and then getting back on course. My Garmin girl gets a little miffed by this but usual gets over it, unless I do it too often in which case she just says "You are 183 kilometres from your destination" with a straight line across mountain ranges and lakes ~ and she has gone somewhere for a smoke, a drink and to chill out a little. I leave it for a while then do a little sweet talking, smile a little ~ then we make up. As I turn away from the resolved situation I find myself talking to myself about how I could be doing all this for a machine that I already paid for.... .... but not too loudly.

Falco.