I’m wondering if I could ask advice from someone with more experience working with QField in broad-leafed woodlands?
I’m setting up a field study into carved nest holes for endangered dormice (family Gliridae) in broad-leafed - Beech and mixed - woodland with a fairly dense understory and canopy in Belgium. Unfortunately, this scenario - understory, canopy and beside large trees - seems to be notorious for adversely affecting GPS accuracy.
My two ideas for improving accuracy were:
Ask QField to average together a large number of measurements - forcing measurements to be taken over an extended period of time (a guess might be 120 measurements which on my hardware takes c. 2 minutes 30 seconds - but that number is pure guesswork and someone with more experience may be able to suggest something better).
Try to get an external GPS receiver which is designed to cope well with these conditions and sends NEMA compliant coordinate information to QField on my smartphone via BlueTooth and is within the limited budget.
I’m trying to get as good accuracy as I can when setting up the field study but I don’t know at the moment what hardware the people monitoring the survey will have.
My phone is a Motorola Edge 60 running Android - I think it has a moderately good GPS chipset - not as good as a specialist high sensitivity GPS receiver but better than earlier smartphones.
I’m using QField 4.2.6 Coral Sea.
(Someone offered use of their Garmin 65a but it doesn’t seem to transmit coordinates in a NEMA compliant format. Qstarz 818GT was another suggestion but I’m not sure how much more accurate it would be than my Motorola Edge 60 and it doesn’t seem to send NEMA compliant coordinate information either.)
Because of the height of the forest canopy, it’s not possible to raise the smartphone above the canopy on a pole - I can climb to a few meters above the ground - above a little of the understory - but I’m not sure if this makes much difference.
Thank you very much. The accuracy can vary depending on several factors that we can’t control (density of canopy, density of understory, etc.) so we’re really looking to get as good accuracy as is practical - c. 1 m accuracy would be ideal but that may not always be possible.
This sounds like a tough challenge! I think that maybe to increase your chances of success you might need some additional equipment, like maybe:
A dedicated GPS receiver that you can set up as a “fixed station”, that you may leave on a clear in the forest (if there is any). This can work like an “RTK” or “PPK” reference that improves on the accuracy of your “rover” GNSS (like your phone, for example). This usually requires to also get a subscription to a network service that helps improve the accuracy of the measurements (although in some countries this is free and it’s usually geared towards cm or sub-cm accuracy).
A drone. Maybe you can walk up to each tree and let an operator follow you and position the drone right on top to get the geolocation.
If you don’t have such a large budget, maybe you can make a first field survey to determine clearing spots on the forest (places where you can get reliable GNSS signal), if such thing is possible. From there, I think QField can really help you with it’s advanced drawing assisting features, check the COGO page of the documentation. With that, and some reference measurements you get on the field, you can easily translate a point on QField from your current, GNSS determined location, to any other point on the map. You might need to bring with you some things to measure distances (counting steps, strings, odometers, range finders, etc…) and/or something to orient yourself and measure angles (probably the compass on your phone can be of help).
External GPS system providers do claim they can sometimes get good results even with canopy and big trees. I have no experience with this myself. But good accuracy can be very costly as well.
Recently I learned about a Trimble solution called Catalyst where a lightweight DA2 GNSS receiver can be paired with a pay as you go RTK service. Subscriptions come at different accuracy levels and have an hourly or monthly bundle, so you only pay when you actually need the service, ideal for seasonal surveys or incidental surveys.
I have tested this personally with QField on an Android phone and it works very good. Set up your phone to use mock location, and it will use the corrected signal, so you can have up to 60, 30 or 2cm accuracy for all your applications.
I use a trimble DA2. They are very good and improve accuracy, the free level is about 1m more accurate than my phone. If you pay you can get upto 1cm but it costs alot. The unit is an improvement over your phone but still is effected by trees but it is an improvement. you can have the unit on a pole in your backpack and have your phone in your pocket so it can track better as well. I like it and would recommend if its in your budget. It also runs on an external power pack so it saves your phone battery.