Locating items on a map

Discussion in 'Designing, building, making and powering your life' started by Tasman, Sep 9, 2016.

  1. Tasman

    Tasman Junior Member

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    Hi All,

    We're on 10 Ha in Tasmania. Even though we're more than 2 years in we still struggle with mapping. Specifically, on a medium size property how to locate and record plants, beds and other features. I need something that works so that I can spend more time doing and less time fighting with tools for planning and recording.

    I've been using QGIS to record our progress. but I can't seem to accurately located items with it. I'm forever resizing and moving features so that new ones fit. So far it would have been better to just not use it, but I'm getting to the point where I want to start sharing what we have done a bit more. GIS seems essential.

    So finally my question:
    Has anybody tried triangulation to achieve this. I can think of two fairly easy ways of doing this. Both would involve making some fixed points on my map and putting big markers there in the real world. Then when I plant a tree:

    a) with a laser rangefinder I could measure the distance to the two points and fix my tree on the map pretty easily. (proclaimed accuracy of laser rangefinder +-1m should be good enough)

    b) with a compass I could measure the direction to the two points and again have a fixed point on my map. (no idea about accuracy)

    Any help appreciated greatly. This is becoming a problem for me.

    cheers,
    tasman
     
  2. 9anda1f

    9anda1f Administrator Staff Member

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    Hi Tasman,
    I think your triangulation approach will work just fine ... after all, GPS is essentially a triangulation scheme (albeit complicated due to the moving satellites). If you can find a transit (in lieu of the compass), you might be a tad more accurate in your angle measurements. I might triangulate from two sets of known points to check/refine your derived locations and the more known points you start with, the easier this would be. With some accurately measured test points compared to the laser range finder, you can calibrate any inaccuracies to get closer than +/- 1 meter.
     
    Bryant RedHawk likes this.
  3. Bryant RedHawk

    Bryant RedHawk Junior Member

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    Cadastral Mapping is always started from a known point. One example of this type of mapping is any geological survey ( The survey by Davey Crocket, of the Louisiana Purchase is one of the most famous ).
    Since this is exactly what you are trying to do, it would be the correct approach.
    I doubt you would want to locate a "Monument" to start from, since you are most interested in only your own property, but it would be wise to survey your parcel and start from one of your corner monuments, so all further measurements are in line with your deeds legal description.

    You need a transit or a compass that you can divide each degree into ten segments, you also need to be able to adjust for demarcation, then you need a way to accurately measure distance. That is about all the sophistication you need. The transit can accurately divided each degree into ten units as well as set the demarcation so you are looking at everything from a true north position instead of from magnetic north position (this fluctuates and is why being able to adjust for demarcation is so important). for taking measurements you can use anything that can be accurately measured and can not stretch or shrink. In the Cadastral Mapping world we used to use special chains or rods since they don't change dimensions easily. The new Laser range finders are pretty good, but if there is a dispute, we tend to go back to the standard chains or rods, since these are the Standards used through out time since they were developed.

    A Chain has links of 7.92 inches, 1 rod = 16 1/2 feet or 25 links, 1 chain = 100 links or 66 feet, 4 rods = 1 chain
    You could also use a fiberglass 100 foot tape measure any longer and you would get to much stretch when pulled tight for taking the measurement.

    The New Laser Transits are very precise and expensive to buy, if you can rent one that would be one of your best bets.

    Redhawk
     

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