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PostPosted: September 22nd, 2008, 8:15 am 
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I am confused. I have been downloading topo maps and printing only those portions of the maps I need. Afterwards, I label the grids where need with the GPS coordinates and other pertinent information. However, I am finding several maps with dual coordinates.

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My question is, which set of numbers should I be using when I have to relabel the grids? Maybe some of my confusion arises from dual zone numbers for one map.

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PostPosted: September 22nd, 2008, 8:53 am 
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I prefer Lat/Lon over UTM, call me old school but it just makes more sense to someone who was raised on lat/lon coordinates*. Just make sure your GPS is set to the correct datum, such as NAD27 as shown in one of your images, and all will be fine. 8)

Zones only apply to UTM, and the fact your map has two zones and two UTM labels just adds confusion. Lat/lon is just one global zone, although the datums can change occasionally.

Tony

*I know, this can be a "religious" type topic and I am sure someone else will chime in on UTM is the best thing since someone thought to put a ground cloth inside a tent. :wink:


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PostPosted: September 22nd, 2008, 11:29 am 
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A segment of the upper Little Churchill crosses the zone 14/15 boundary.

I suggest you use Google Earth to see this. Select Tools>Options>Show Lat/Long UTM.

Next Select View>Grid

You choose, as Tony advises.


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PostPosted: September 22nd, 2008, 12:24 pm 
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On the Mac platform,

Google Earth >preferences>on the 3D view TAB>under the show lat/long select the Universal Transverse Mercator radio button. Then click the Apply button (lower left side) and OK (on the right)

Next Select View>Grid

Both lat long and UTM are good systems, different but similar. As an ex Naval Officer, I love lat & long but while canoeing tripping, it is easy to call to your neighbouring canoe a UTM coordinate of something.

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PostPosted: September 22nd, 2008, 3:16 pm 
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Quote:
*I know, this can be a "religious" type topic and I am sure someone else will chime in on UTM is the best thing since someone thought to put a ground cloth inside a tent. :wink:


It's not that complicated....if you pee in the lake use UTM, if you bushwack 100 meters from shore use lat/long. :roll:

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PostPosted: September 25th, 2008, 10:48 pm 
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Worth,

It's quite simple: ignore the brown grid marks.

NRCan prints (in brown) the coordinates of the neighbouring UTM zone on maps that touch a zone boundary (the boundary will either be the left edge of the map if it is at the western extremity of a zone or vice-versa: no large-scale NTS sheets span a zone boundary). The blue grid that covers the map corresponds to the blue figures in the margin (which are the correct coordinates for the UTM zone in which that sheet lies).

A good reason for using UTM coordinates with a GPS is that is is much easier to locate your position on the map using the blue UTM grid and labelling in the margin than it is to use the (non-existant) lat/long grid printed on the map and the (quite hard-to-read) labelling of it in the margin.

HTH

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PostPosted: December 30th, 2008, 4:39 pm 
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One thing to watch is that your datum on your gps matches the topo map you are using. I see this happening as most maps we use are nad83 but then you will be using a nad27 forget to change the settings and you are out by a couple hundred meters.

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PostPosted: August 19th, 2009, 4:16 pm 
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dksmith wrote:
One thing to watch is that your datum on your gps matches the topo map you are using. I see this happening as most maps we use are nad83 but then you will be using a nad27 forget to change the settings and you are out by a couple hundred meters.


I'm trying to deal with this at the moment. How do I know what datum I'm supposed to be using? I'm trying to put the 6-figure grid references from Laurel Archer's guide book (Northern Saskatchewan Canoe Trips) into my GPS (Garmin GPSmap76) using the supplied MapSource software and the Garmin Topo Canada version 2.00 maps.

In the MapSource software I can go into the preferences and select the "Position" tab which gives me two drop down boxes, Grid & Datum. Under the Grid box I have MGRS selected and under the Datum field I have NAD83 selected. That seems to get me pretty close (closer than I had it before reading this thread), but it's not there yet.

Any advice is appreciated!

Thanks in advance,
Bryan

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PostPosted: August 19th, 2009, 4:31 pm 
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If the author of your guide book doesn't say which nad he used, then you are just kind of guessing. If you enter your waypoints manually, you should be able to switch between 27 or 83 on your GPS or on your computer. By comparing the positions to obvious things, such as starts of portages and such, you should be able to determine which NAD was used.

At the same time, different GPS have different levels of accuracy. My old etrex was far less accurate than my 60cx...so referece points are often off by 50 to 100 meters. In any case, i don't think exact accuracy is all that important...your gps will tell you something is coming up, so you'll be on the look out for it.


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PostPosted: August 19th, 2009, 5:44 pm 
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Im a HUGE fan of MGRS.Its all I use.very simple very accurate

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PostPosted: August 19th, 2009, 6:03 pm 
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Response to Bryan's post:
I used Laurel Archer's book for our Churchill trip (Patuanak to Sandy Bay).
All my topos used NAD27; I checked every one in the lower left corner. You will find a list of those topos in my Churchill report.
For every feature I checked, and there were many, her UTMs agreed with those on the topos.
So it figures that her UTMs are NAD27 for those Churchill topos.

More generally, as others have pointed out, I can't see how you can possibly use latitude and longitude in conjunction with Canadian topos. The latitude-longitude grid on those topos is far coarser than the UTM grid.

Yours in paddling, Allan

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PostPosted: August 20th, 2009, 3:01 am 
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OK, I think I'm learning a few things as we go: MGRS = Military Grid Reference System, A metric grid system that is a subset of the UTM system. NAD27= North American Datum 1927.

Thanks for helping me along the curve folks. Thanks Allan for offering me the shortcut to figuring out what I need!

Bryan

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PostPosted: August 20th, 2009, 7:10 am 
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I expect that most people know this but here goes anyway.

Archer and Marchildon-Robinson use a 6-digit grid reference system, for example 123789.
BTW, I prefer to write this as 123/789, for quicker recognition.
The first is the easting, the second the northing.

Your GPS gives the easting first then the northing, each to 7 digits.
To get the 3 digits from the 7, drop the first 2 digits and round the rest.

Unfortunately, knowing the map number, for example 73P/10 (most paddlers use 73P10 instead) and the 6-digit number is insufficient information to locate the position on the map.
You must know also whether the map is based on NAD27 or NAD83. I have seen differences of several hundred metres between the two.

I could find no statement in either Archer or Marchildon-Robinson regarding whether they used NAD27 or NAD83.
As I remarked previously though, I'm convinced that the maps they used are based on NAD27, for the stretch of the Churchill that we paddled.

Things were confusing enough before the advent of the GPS. Now there is an additional complication.

A paddler wishes to record the position of a campsite.

If s/he has no GPS, s/he goes to the map, locates the position of the site, looks at the lower left corner to determine whether it uses NAD27 or NAD83, and reports:
73P10, 171/680 (NAD27)

If s/he has a GPS, s/he goes to it, pushes the buttons and records the two 7-digit numbers; she must record also whether the GPS is set to NAD27 or NAD83.
But what happens if the GPS is set for NAD83 and the topo available to a second paddler is NAD27? The second would seem to be out of luck.

Toporama is down at the moment (has been down for almost a full day now); I can't address some other matters until it is up.

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PostPosted: August 20th, 2009, 7:20 am 
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Toporama is working for me
http://atlas.nrcan.gc.ca/site/english/maps/topo/map

Frequently asked questions:
http://atlas.nrcan.gc.ca/site/english/m ... o_faq.html

Natural Resources Canada - Mapping
http://ess.nrcan.gc.ca/mapcar/index_e.php



Barbara

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PostPosted: August 20th, 2009, 7:51 am 
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The Toporama site is up but is not functioning properly.
Try clicking on the main map.

Perhaps I should explain why I want to get to Toporama in connection with this matter.
You can get UTMs (and latitude/longitude coordinates) from Toporama, but I don't recall being able to determine which system (NAD27 or NAD83) is used.
So knowing that my Churchill maps use NAD27, I would go to Toporama, click on a location for which I know the NAD27 coordinate, and see whether I get the same number.

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