GPSMap 76CSx for survey work?

Discussion in 'General GPS Discussion' started by JayArr, Aug 7, 2022.

  1. JayArr

    JayArr

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    Hi All

    Here's my objective:

    Use a GPS to locate the survey pins on a piece of land I bought in Nova Scotia Canada.

    The Plan:

    I have a single GPS coordinate on the survey that locates what is called a "co-ordinate Monument" which is placed by the government. From there I have a series of instructions in the form of angles and distances. Example - 143 46' 38" 140.94feet

    I've got a guy on Craigslist selling a working 76CSx for $120Cdn ($95US?) which sounds like a decent price to me.

    The trouble is that it has no purchased maps and it was only used on the west coast in British Columbia.

    So here's what I can't figure out. Will it have a base map for Nova Scotia at all or is it possible it only ever got a western section of basemap?

    Second question: If it has a basemap for Nova Scotia do I really need anything more to go bushwacking to find my pins?

    As I understand the operation I can input the GPS coordinates for the monument as Waypoint "1" and then "project" a second waypoint by entering the angle and distance. This would give me Waypoint "2" as my corner pin. At that point can I wander around the bush and have the Garmin tell me hotter/colder, left/right sort of thing until it tells me I'm standing on the projected waypoint? Sort of like geocaching for a survey pin right? I've done lots of geocacheing with phones but never owned a Garmin. I suppose that I then put the next angle/distance in and head out in the direction it tells me. I repeat until I've found all my pins right?

    If that works without having to buy any topographical maps then I'm all set and I'll buy the unit tomorrow.

    Any comments, caveats or warnings?

    Thanks in advance for your help!
     
    JayArr, Aug 7, 2022
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  2. JayArr

    Nuvi-Nebie Moderator

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    You don't need any maps to do what you want to do, it is possible to enter a latitude / longitude coordinate as a waypoint and then project further waypoints from it onto a completely blank background, the GPS will display the waypoints on screen and you can select (find) a waypoint and 'GOTO' it, this will display your current location and a straight line to the waypoint.
    You will also have a compass screen showing an arrow direction and distance to waypoint

    You can create all the waypoints before you go to the area as the first point is an actual co-ord, the second waypoint is projected from the first and once you have waypoint 2 you can project from that to create waypoint 3 an so on

    You could also generate all the waypoints using the free to use Garmin Basecamp and then enter the 'real' co-ordinates into your smartphone and treat them like Geocaches, having created the first 'real' Waypoint you would zoom in on it select the MEASURE tool, click on the Waypoint and 'Measure' the distance / direction and create a second Waypoint at that spot, then repeat the process to create the other Waypoints
     
    Nuvi-Nebie, Aug 7, 2022
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  3. JayArr

    JayArr

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    That's great news! Thanks for the reply Nuvi-Nebie.

    I pick up the GPS this morning and will load BaseCamp today to figure it out.
     
    JayArr, Aug 7, 2022
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  4. JayArr

    JayArr

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    It doesn't look like there is a function to "project Waypoint" within the BaseCamp software. I have created my first reference waypoint based on the government coordinates but can't project from there using an angle and distance.

    I'll try again later today when I get the actual GPS.
     
    JayArr, Aug 7, 2022
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  5. JayArr

    Nuvi-Nebie Moderator

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    I explained how to 'project' in Basecamp in post #2, eg. Use MEASURE
     
    Nuvi-Nebie, Aug 7, 2022
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  6. JayArr

    JayArr

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    Using Measure isn't accurate enough, it only has one decimal place on the degrees and it measures distance in miles.

    The GPS was a bit of a disappointment as well, I had hoped to input the exact numbers from the survey in degrees/minutes/seconds.xxx but was only given space for degrees and one or two decimal places.

    I found a solution though, I used a geocache website that allowed fine grain projections and returned a result in degrees/minutes/seconds.xxx. Then I just manually input the pin locations as waypoints into basecamp, hooked up the device and uploaded them.

    I think I'm all set to go now.

    Thanks for all the help, I'll post up on how well it all works!
     
    JayArr, Aug 8, 2022
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  7. JayArr

    Nuvi-Nebie Moderator

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    If you zoom in (as detailed in post # 2) the miles will change to feet
     
    Nuvi-Nebie, Aug 9, 2022
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  8. JayArr

    JayArr

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    Well, yes, it will, but the first pin on my land is 4939.81 feet from the survey monument at an angle of 299 48' 21". If I zoom out to show both waypoints the measurement is in miles, if I zoom in until the measurement is in feet I can only see the monument and the map won't shift when I hit the edge. I suppose I could convert feet to miles but since the angle was only to one tenth of a degree in measure mode it was easier to go outside the Garmin software to do the projections.

    In the end it appears that the Garmin software was written for a specific purpose and it wasn't survey work. My attempts to use it in place of very expensive Transoms and survey gear is bound to run into a few problems. This is not a reflection on the Garmin, just a necessary adjustment to apply it to a new purpose.
     
    Last edited: Aug 9, 2022
    JayArr, Aug 9, 2022
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  9. JayArr

    Nuvi-Nebie Moderator

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    I would agree that both Basecamp and in-built GPS projection is not sufficiently accurate for land survey, however there is another problem to concider, the GPS that you are tranfering these very accurately calculated measurements isn't good enough for land survey either, if we use an initial position of N49 W122 and project 5000 feet at 299 degrees and compare it with 5000 feet at 300 degrees we see that a whole degree moves the projection by about 80 feet, so 0.1 of a degree is about 8 feet. The accuracy of this kind of GPS could easily be no better than 20 feet so fractions of a degree or a foot are of no use

    You would have to spend thousands (or tens of thousands) of Dollars to get a surveying GPS that could accurately plot 4939.81 feet or an angle of 299 48' 21".
     
    Nuvi-Nebie, Aug 10, 2022
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  10. JayArr

    JayArr

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    That's interesting, I was under the impression that modern GPS's were accurate to within about 5 feet if they could get signals from enough satellites. I guess that's still not the case and I was wrong about that.

    That would certainly explain the lack of granularity on the part of the software, the coders at Garmin likely saw no need to calculate points with more accuracy than the receiver could find them.

    I hope I can still find my pins.
     
    JayArr, Aug 10, 2022
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  11. JayArr

    Nuvi-Nebie Moderator

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    I don't think you will have a problem finding the pins, it's just like geocaching you will be directed to roughly the right spot and then you have a look around, there will probably be other clues such as a fence, a path, edge of a pond etc. to help you, if you have difficulty finding them I would mark a spot you have been directed to and then approach the same pin from a different direction and place another marker, obviously your two markers should be in the same place but they probably won't be, you could even try again from a third direction, you now have three markers in a triange with (hopefully) the pin inside the triangle

    This is why location finding can vary, if you go for a walk with your GPS it can draw a trail of where you have been, BUT if the GPS is stationary it will reveal this :-

    jitter.jpg

    It looks like the GPS has been wondering about, these are all errors, so where is the real location ?, probably in the middle of the points if you average them all into one spot
     
    Nuvi-Nebie, Aug 10, 2022
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  12. JayArr

    JayArr

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    That's brilliant advice, I never would have thought of triangulating like that. Thanks.
     
    JayArr, Aug 10, 2022
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