I had a few questions about setting up a UAV survey with an RS2 and/or M2s and GCPs. Up until now we haven’t needed this level of accuracy so it’s been interesting to figure out how you do it. I will say there may be completely incorrect statements made below if I’ve misunderstood some of the practices. Also, fellow posters and this forum has been immensely helpful. Thanks!
Our setup is two RS2s, a drone, and a multispectral camera (Micasense RedEdge-MX). I’m trying to figure out if using an M2 with a RS2 base is worth it over collecting GCPs. The areas we will be flying are not large (max 150 acres).
For those new to this area like us, I found this thread particularly helpful: Reach RS for GCPs and UAV mapping
In our case we will not have any known points for the base, but we are in Canada so we can submit our RINEX file to NRCAN for post-processing. But we do not care about the global location, just the relative location within the property. So perhaps this processing is not necessary?
My understanding of the UAV survey setup is as follows:
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Setup up the RS2 Base, allowing it to collect data for 1 hour.
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Lay out a number of ground control points, in our case I’m thinking 6, around the property. Use the RS2 Rover to collect a point at each GCP.
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Fly the drone survey using a flight planning app.
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Post-process the data, using software like Pix4D to create an Orthomosaic. The camera we are using has an in-built GPS which will make processing the images easier.
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Georeference the images to the GCPs using software like Pix4D or QGIS’ georeferencer function.
At this point, while the survey won’t be centimeter accurate to a global reference system, it will be centimeter accurate relative to the property itself. Given that we will want to come back and use the same base position, our rover and drone will have that level of accuracy going forward. If our clients want to use their own GPS system (likely handhelds like Garmin or tractor-mounted) to investigate specific points, while the survey will not be centimeter accurate for their devices it will be accurate enough they can within a meter of the points (including the the positioning error in their non-RTK GPS systems).
Assuming this is correct, I have a couple of questions:
a) An alternative to GCPs is hooking up an M2 Rover directly to the Micasense camera (instructions here).
Theoretically, we then would not need GCPs as we would have centimeter accuracy just with the RS2 base and M2 rover (relative to the property). But, with this specific camera it seems it would take more post-processing time as the M2 data can’t be written directly to the camera. From Micasense:
NOTE: The Emlid Reach GPS does not output Ublox GPS packets at this time, so GPS coordinates will not be written to the image metadata. A python script is provided below to assist in creating a geolocation file to use with Pix4D, to associate image number with GPS coordinates.
b) Is there a significant amount of post-processing time to get this GPS information? Our specialty isn’t on the GIS side, so I’m trying to create a workflow that keeps GIS processing to a minimum.
More specifically my understanding is that we will be able to upload the images directly into software like Pix4D and because each image has GPS information from the camera it will easily stitch an orthomosaic. Then we would just need to georeference in our 6 GCPs to get a sub-cm accurate image relative to the property. Is this correct or is there significant processing time I’m missing?