New to reading gps,need a bit of help. - ClubTread Community

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post #1 of (permalink) Old 07-24-2014, 11:45 PM Thread Starter
Hittin' the Trails
 
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Default New to reading gps,need a bit of help.

I have read " Gps Made Easy" plus my Garmin eTrexLegend booklet ,and today in my wanderings took a reading of 11 U 0670909..UTM 5615281,or to condense it GR7090915281 ( I think) but In Gillean's books ( Kananaskis Country Trail Guides) She would have shown it as GR709152, or so it seems. I was near Windy Ridge which she shows the summit to be at GR71648 .So my question is although Gillean leaves out the one's and ten's digits ( or at least I think thats correct ,but I could be wrong in all this) would her points of reference be accurate to 100 meters? It seems that is quite a distance,but since were not involved in military percision,and only hiking to an obvious summit, or lake etc, this would be all a hiker would need.
I always set my gps unit on the summit and photograph it's reading and they are what Gillean says they will be. Well she doesn't always include the summit GR's but where she has I found them to be what my Garmin unit shows, I'm just getting all this GPS stuff figured out now ,but have had the unit for a couple of years.
Can someone tell me if I have this figured out correctly please? Warrning, if you answer,you might find me asking you many more gps related questions .
Thanks, Neil
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post #2 of (permalink) Old 07-25-2014, 08:51 AM
High on the Mountain Top
 
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I just hack at this and mainly use my GPS to get grid references to confirm on the maps. Or sometimes to compare an exit to an uptrack if things look 'funny' and I want a second opinion. One of my hiking partners calls it the "cheater box" and it comes in very handy from time to time.

Grid references are the middle three numbers - the last two make a more accurate reference but for map purposes are generally redundant due to the scale of the map. Maps will indicate what to set the GPS to, NAD 83 etc, so the map and GPS speak the same language. I would say you are on the right track.

Depending on what vintage of Dafferns stuff you are using there were some erroneous grid references (wrong UTM used or something like that which put the grid references just enough out of whack to confuse) and there are always risks of typos on such things. I forget exactly what the issue was but perhaps a google search would dredge that up.
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post #3 of (permalink) Old 07-25-2014, 09:08 AM
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Damn, what did we do before google! Part way down the page describes the Daffern guide issue. Also some good references on using the gemtrek maps with a gps.

http://www.gemtrek.com/faqs.html
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post #4 of (permalink) Old 07-25-2014, 10:23 AM
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I believe the newest KCTC edition now uses NAD 83, but the older ones (the 2-book 3rd edition from 1995ish) used NAD 27, which became REALLY outdated along the way.

If you have 11 U easting: 0670909 northing: 5615281, then you pull the relevant digits of:
easting: 06(709)09 and northing 56(152)81,
which condenses to a 6-digit grid reference of:
GR709152.
You will also see this called Military grid references, as it is based on the common practice.

You would never condense it to GR7090915281. That would be a number no-one has any clue how to parse.
You either use the full references, or the 6-digit.

The GR you quoted has only 5 digits, which would again not be used. If it was, for example GR071648, then to put that in your GPS, you would pull out the relevant information:
easting: __071___ northing: __648__.
The end digits, you just zero: ( __07100 , __64800 ), and to get the front digits, check on your map for what's in the area. (probably an 06 or 07 for the easting, and a 56ish for the northing).

If you look at a map, it makes more obvious why we use the three significant digits, since the map UTM grid usually only shows two significant digits, dropping the front ones, and and we guess the 100m based on battleshipping the point within the 1km square.

So just make sure that you set your GPS to the datum your map or book is using, and you're good. You can even use the GPS to convert datums if your book and map are different, but with the new KCTG, you should be fine.
And oh, while we're talking datums, be aware that for recreational activity around here, NAD 83 is functionally equivalent to WGS 84.
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post #5 of (permalink) Old 07-25-2014, 01:29 PM
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Rachelo, one of the best summaries I've seen.

Personally, I get annoyed by the 6-digit short reference. There have been one or two times where I haven't known the first 2 digits and no map readily available. Grrr. Extra work! (not that it can't be figured out, but I like quick 'n easy)
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post #6 of (permalink) Old 07-25-2014, 01:36 PM
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Quote:
quote:Originally posted by guntis

Rachelo, one of the best summaries I've seen.
+1
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post #7 of (permalink) Old 07-25-2014, 01:39 PM
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Quote:
quote:Originally posted by guntis

Rachelo, one of the best summaries I've seen.

Personally, I get annoyed by the 6-digit short reference. There have been one or two times where I haven't known the first 2 digits and no map readily available. Grrr. Extra work! (not that it can't be figured out, but I like quick 'n easy)
The grid reference is to a point on the map, not a point on the Earth. If you aren't using a map, use lat-longs instead.
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post #8 of (permalink) Old 07-25-2014, 04:18 PM
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WGS84 is not equal to NAD83, although the two datums are close for most of North America.

Here's some more detail: http://mappingcenter.esri.com/index.....answers&q=740

It's important to understand datums and projections when using GPS and maps! Especially if you wander all over the world or go places, like northern Canada, where the UTM projection isn't very useful.
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post #9 of (permalink) Old 07-25-2014, 05:01 PM
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Thanks.

Quote:
quote:Originally posted by Dru

The grid reference is to a point on the map, not a point on the Earth.
I like that way of putting it.

I used 6-digit grid references on maps for many years before I had a clue what UTM was or the use of full coordinates, or owned a GPS.


Regarding WGS84 and NAD 83, I apologize for simplifying too far.
For recreational activity in our area, WGS 84 and NAD 83 are functionally equivalent.
If you're near the pole, you probably shouldn't be using UTM at all.
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post #10 of (permalink) Old 07-26-2014, 05:17 PM Thread Starter
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Thanks for the great info, I made a mistake ,it should have been GR 716148 That Gillean's book showed, I left a digit out. ( Sorry Gillean). I had a hard time getting it through my head that the before anything ,one needs to pay attention to the zone,then pick out the right map in the correct longditude , in this case it was 11 U , then the easting and so on.. I got it now. Yes as someone said Rachelo , your explanation was the best ever, you should have written the book, ( it's not to late). Thanks everyone..
Neil
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