Hi Guys,
I’ve just received my Reach RS kit which I plan to use for laying GCP’s from which I will require absolute accuracy for most of my projects. It’s my understanding that in order to get an accurate absolute accuracy without having an available pre-surveyed point I’ll either need to setup a NTRIP connection in the field or post process against my nearest station’s RINEX files. As some of my previous works have been done in places without reception to setup a VRS I’m looking at focusing on the post processing option.
With this in mind, my planned workflow has been (for sites without a pre-surveyed point available):
- Place base station (Average single position) and leave RAW logging enabled for at least 20 minutes.
- Perform survey with rover using LoRa RTK connection.
- Post process base station files:
- Convert RAW u-blox to obs,nav & sbs using RTKCONV
- Covert .17d Rinex files to .17o using CRNX2RNX (if I skip this step, RTKPOST doesn’t seem to be able to read the files)
- Process base vs CORS using RTKPOST as shown in the image below:
- Calculate the average position values given in the output .pos file.
- Calculate difference between post processed position vs the base positioned used during the survey.
- Offset all surveyed positions by the value calculated in the previous step.
- Convert values to GDA94 and AHD.
At this stage, I’ve tested setting my base station up on top of two pre-surveyed points and then tried post processing the raw logs to see how accurate my positioning is, with the distance between my base and the reference station being 16km and 12km. However, upon comparing my post processed average position with the surveyed position (translated ITRF2008->GDA94), I’m getting large errors. Today’s test resulted in errors of about, 0.96m E 1.93m N and 1.97m Z.
The files I’ve used are in this dropbox folder:
The base was placed on top of the following point(GDA94):
-
27º 33’ 42.75271" S
-
152º 56’ 25.52630" E
-
494118.814m
-
6951327.940m
-
29.171m AHD
I’m going to keep investigating why I’m getting the error but I think it could be either:
- Incorrect post processing
- Poor base placement (base could only see 12-14 satellites, on a previous trial I had 20-22.
- Incorrect CRS transformation
Any help with troubleshooting where I might have gone wrong / any help with correcting my workflow to be more aligned with surveying practices would be greatly appreciated.
Cheers,
Ben