Here is our new online talk with an Emlid user! We invited @RoryG from the United Kingdom to discuss workflows for PPK and RTK missions with DJI Phantom 4 RTK and Reach RS2 as a base station.
Rory is a qualified geologist, GIS specialist, and drone pilot. He eagerly shared his RTK and PPK mapping experience, from placing the Reach base and connecting it with a drone via the Emlid Caster, to processing imagery in photogrammetry software. Moreover, Rory compared the accuracy results of RTK and PPK missions and gave lots of mapping tips for drone pilots.
Curious, I see your BENCHMARK (basemark) where your RS2 is set manually upon is 155.342m for the ellipsoidal height. (26:17)
And at (38:59) your height 106.081m, a difference of 49.261m.
Is this the resulting 106.081m orthometric height and matches what is published for this benchmark (basemark) your set upon?
Did you use a GEOID to achieve this? I guess in your ArcGIS or QGIS software (after the fact or real time) or in real time via Emlid ReachView 3 using coordinate system and geoid?
(35:26) Is the altitude shown in Metashape the relative height from take off of the drone? (0m)
Wonder how you localize to something like this to get the ACTUAL terrain level? I assume just obviously use / tie into the benchmark and it’s published height since a KNOWN point / benchmark is available?
Thank you!!
The Z height is always tricky I think most and what is out there seems to be left desired. : / Would be AWESOME to see a lengthy DETAILED video from EMLID about Z height, elevations, datums, orthometric, elipsoidal height, geoids AND LOCALIZATION etc. Seems to get off on the right foot of a project whatever it may be, this is very critical.
Thank you, glad you enjoyed it! When surveying using WGS84 (or whatever ITRF you are using) the base and rover positions always use ellipsoid height. When we convert to OSGB1936 it transforms to geoid height, to achieve this we have the OSGM15 geoid model installed in Agisoft Metashape Pro.
ReachView 3 can also survey in local coordinate systems such as OSGB1936, but you will normally need to download a geoid to the app to achieve this. For PPK / RTK applications you must always use ellipsoidal height or you’ll run into problems further down the processing line. To be clear, RV3 is only used in the video workflows to set up the caster or to enable logging. The survey part of RV3 is irrelevant for RTK / PPK (unless you are measuring GCPs, however I would recommend recording your GCPs in the same coordinate system as the flights).
It can be a minefield and a lot of folk stumble over ellipsoid vs geoid heights. For us in the UK it’s fairly simple, we have a network of national reference stations in ETRS89 plus ellipsoid height which transforms directly to OSGB36 plus geoid height. There are several localised height references in the UK geoid model depending what part of the country you are in, the one we use is Lerwick but there are separate geoid heights for Northern Ireland, Orkney and the Western Isles. Each datum is included in the geoid.
