New Feature for SARtopo?

nimdokk's Avatar


10 Dec, 2017 04:48 PM

I'd like to suggest an option in the Lines element and that is to create a line with a width measured in feet, yards, meters. This could assist search managers in determining coverage if the Range of Detection could be set to indicate how wide a resource could see. That way if a grid search team all had GPS units, when those tracks are imported, the AMDR could be specified and then viewed in the map to detect gaps in coverage. This would be similar to the "Buffer" element. Or if there was a way to convert a line into a buffer.

I'm sure there is a lot of other work that needs to be done ahead of this but it would be a nice feature.


  1. 1 Posted by caver456 on 10 Dec, 2017 05:17 PM

    caver456's Avatar

    Hello, just wanted to chime in that there's a lot of inherent danger here
    in putting too much faith in what the GPS tells you. Our team has gone
    through the wringer on this same topic a few times. If the 'radius' of
    uncertainty in the GPS fix is 3 meters - which is incredibly good and is
    probably not a realistic expectation unless you are searching a prairie -
    then your line would have to be 12 meters wide (double the radius to get
    the diameter, then double that again if it's based on a track that someone
    else created while hiking who had the same 'radius' of uncertainty) before
    it could have any statistical relevance. That could be a realistic
    critical separation in a prairie, but, as you hit vegetation or terrain and
    the radius of uncertainty increases while the critical separation should be
    decreasing, the problem increases geometrically. More over, you'd be
    directing the searcher to follow the centerline of a hypothetical but not
    realizable buffer. Basically like all the "ideal" physics questions in
    school. "For this question, ignore friction, ignore elastic collisions,
    assume it is in a vacuum, etc etc etc." Basically using a line drawn on a
    computer to guide a searcher in the field to an accuracy anywhere close to
    the critical separation is just not realistic. Sorry to be a wet blanket.

  2. 2 Posted by nimdokk on 10 Dec, 2017 05:46 PM

    nimdokk's Avatar

    Good points about the accuracy of GPS units. The example I am looking at was in fact a grid search in an open field. We only had units on the end people and after I imported tracks, I put polygons in so I could more easily identify gaps in coverage to back up my debrief that we had a low POD for the area and it needed a second pass by another team. Might not work so well in denser vegetation with tree canopy to consider. There may be other ways to go about achieving more of a visual representation of what was covered and how well it might have been done.

  3. Support Staff 3 Posted by matt on 10 Dec, 2017 06:35 PM

    matt's Avatar

    For technical reasons, I can't trivially set line width to a real-world measurement as opposed to e.g. 5px. However I fully support adding buffers to the convert context menu, which would let you accomplish this by converting lines into buffers - although you'd need to do it line-by-line, as there is no bulk convert feature. I didn't do that when I initially added buffers because there were some technical hurdles and I wasn't sure what the uptake on buffers would be, but they've proven themselves.

  4. System closed this discussion on 02 Oct, 2019 04:24 PM.

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