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Hi all,
does anyone have any recommendations for recording NGRs on site surveys, fieldwalking etc.? Do you still use hand-held GPS devices or have smart-phones taken over? If the latter, what apps do you use? I imagine software that doesn't rely on a phone signal would be pretty essential.
Cheers,
Tom
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If its spot locations try using hand held GPS devices in conjunction with google earth.
You can also convert long and lattitude from google earth into NGR's with
http://www.ordnancesurvey.co.uk/gps/transformation for instance.
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Handheld GPS e.g. Garmins are pretty much standard when I've done walkover survey. Phone GPS can be used (battery life can be more of an issue than with handhelds), but make sure it's a phone that doesn't have A-GPS (i.e. one that needs a data signal to boost the GPS). On Android the app GPS Status is very good (I've found) and can give you co-ordinates in OSGB NGR.
With both phone and handheld GPS you'll struggle to get a better accuracy than ca. 4.0m in my experience
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I use a fabulous app called geopaparatzzi. which even connects with GIS - is free and can collect data, photographs, locations etc. bloody marvelous
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VGC Wrote:With both phone and handheld GPS you'll struggle to get a better accuracy than ca. 4.0m in my experience
The trick is to use your handheld to also record the location of a few landmarks that might appear on the digital maps i.e field boundaries. road junctions etc as well as your specific survey spots. Hopefully therefore if the survey 'error' is consistent across the area you can 'correct' the survey to a higher degree of accuracy back in the office.....
With peace and consolation hath dismist, And calm of mind all passion spent...
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Bear in mind the direction and magnitude of "error" of a single GPS reading on a stationary device (when not using corrections from a base station) "wanders" over time, so if you want to tie in to nearby fixtures you need to be quick about it! After all, you want to have the same error on your control points as on your captured features. But the principle is sound - the "error" will be the same over a wide area at any one moment in time. (All to do with which satellites are seen, and their true known positions...)
Using features from OS mapping as a control is itself inherently risky, because their lines are only accurate to a set tolerance based on map scale. Even if you get a co-ord down to the nearest mm when you interrogate with your GIS, the data may only be accurate to the nearest 500mm as captured. After all, it just has to look right when viewed at the chosen map scale. (Also, where things are so tightly packed that they turn into an inky blob, the OS tend to "ease" them a bit for visual clarity.) And that doesn't even take into account the correction factor between GPS and terrestrial map projections!
Best to just accept that data from a typical hand-held is within a few metres of truth, which is usually fine for fieldwalking, photo surveys, big landscape surveys, etc...
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7th July 2014, 12:17 PM
(This post was last modified: 7th July 2014, 12:21 PM by tom wilson.)
Many thanks guys.
Accuracy isn't a huge issue as I'm only likely to be doing fairly coarse stuff. One of my main requirements is for locating HER sites, which in some cases seem not be visible any more so in that case I just need to confirm that, "no, there is no longer a 20m mound in this part of the field".
Geopaparatzzi looks great...if I'd only listened to BAJR's advice and got an android...might have to go buy another handheld after all..
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Out standing in a field but haven't a clue where I am?
I once had this job in Australia collecting soil samples looking for gold and we were given satellite pictures and we would put pin pricks on the photo and mark on it the sample number. it's a bit like using permatrace. Don't think I ever found any gold for the company. (not that they would tell you hay).
.....nature was dead and the past does not exist
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kevin wooldridge Wrote:The trick is to use your handheld to also record the location of a few landmarks that might appear on the digital maps i.e field boundaries. road junctions etc as well as your specific survey spots. Hopefully therefore if the survey 'error' is consistent across the area you can 'correct' the survey to a higher degree of accuracy back in the office.....
Well indeed. It's also worth recording the accuracy of each location, as you can then use this to buffer the points in GIS if you're into that kind of thing.
