Question about (the necessity of) datum transformations for RTK GNSS using u-blox F9P
Hello dear people, I am here because I need your help. I am part of a university students project in Germany. Our task is to build a UAS/UAV, which flies a survey mission above a certain area and map the location of targets on the groud (with 1 m precision), which have to be identified with an onboard camera.
For this purpose we have decided to use RTK for the UAS’s navigation, and have purchased two u-blox ZED-F9P GNSS modules to be set up as base and rover. Now here comes the problem:To set up our base station (i.e. find out it’s precise location), we want to use the F9P’s RTK ability and use the german state-run NTRIP caster service called SAPOS, which is available for free. The problem is, SAPOS sends it’s correction data in the ETRS89 reference frame, while we have to present the target locations in WGS84. The F9P’s manual states, that the RTK solutions the GNSS-chip puts out, automatically switch to the reference frame used in the correction data and that, if another reference frame is required, a datum transformation has to be performed. The u-blox Chip offers configurations to input several transformation paramters, but I don’t have a clue on where to find those parameters.
While searching the Internet for Information, I have found out, that between WGS84 and ETRS84 (or the most recent realization thereof) there is a difference of about half a metre, which is of no concern for most appications, therefore both CRSs are sometimes treated as equal. In our case however, 0.5 m could mean the difference between staying within the 1 m precision-limit or not, because we also expect some inaccuracy due to the whole being-on-a-plane-thing. While trying to look up transformation-parameters, the closest thing to what I THINK I am looking for is this, but this again seems to tell me, that there is no difference between ERTS89 and WGS84 at all. On top of that, I did read something about different types of coordinate transfomations having different accuracies, which could be another error source to consider.
Right now I am utterly confused about the whole CRS/datum topic and don’t know where else to look for information regarding my problem. I am uncertain about, whether I should dive deeper into the topic, or if I maybe just get away with ignoring the whole thing. At the moment our GNSS is totally able to get RTK-fixed solutions using the abovementioned SAPOS-Service, I just don’t have any way to tell the “absolute” precision of these fixes, or in which datum format they actually are.
Maybe there is someone on this forum, who has experiance whith the topic, who can provide me with some explanation or a push to the right direction. Also any links to Information, which answeres my question or provides the necessary background would be very much appreciated.
Thank you for reading!
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