Surveying An RT Base-S Antenna Location Using an RT and RINEX File

Step 1. Surveying

Set the RT next to the base station antenna with a power source, connect the base station antenna to the RT and be sure to disconnect any radio modems etc. that would normally feed corrections to the RT.

The configuration on the device is not important as we will not be initialising it.

Leave the device on for a time (ten mins or so), this will log an RD file on the device containing all of the raw GNSS observations. 

To retrieve the logged RD file from the RT.

1. Power on the unit and connect via Ethernet.
2. Connect your PC to the RT unit either through a network or directly via a crossed RJ45 connector.
3. Open windows explorer (any folder or "My Computer" will do initially) and type ftp://x.x.x.x (where x.x.x.x is the IP address of your unit, e.g. ftp://195.0.0.64) into the Address Bar.
4. You can now move, copy or delete any of the RD files.

The RD files use the format YYMMDD_HHMMSS.rd. This is the date and time (GPS clock time) of the first GNSS update. If no GNSS data is received for the duration of a file, then it will be called mobile.rd.

Copy the relevant RD file (likely the most recent) and you can then post process it using a RINEX file from a local network base station (OS, CORS, SOPAC, etc.), as detailed in this guide on post processing with RINEX files. Also be careful to take note of the datum used in the RINEX file as it may differ from the expected WGS-84 used by the RT.

This will yield an NCOM file which will contain the raw values for the lat, long and altitude. You could also extract the CSV from this and do some averaging if you wish or just pick some representative position values from the NCOM file directly. Either way take note of the lat, long and alt you wish to use.

Looking at the NCOM file in NAVgraph you should be able to see something like what I achieved below. Note that the GNSS position mode ought to be 24 - gxInteger if the RINEX file was used correctly (red trace, RH axis).

Setting the cursor to the max and min values for latitude (red circles), you can then read off the values at each point from the data table.

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In my case the values are the same to the 8th decimal place, so my variation is in the mm scale here (see this article for supporting information).

You can repeat a similar process for longitude and altitude or export the CSV and take an average.

Step 2. Loading to Base-S

Connect to your Base-S over Ethernet and "read your configuration from device". Then click next to go to the Status page. Then click on the Position Manager button, Add new position, enter you lat, long, alt and an appropriate name, then click OK. This will now have committed the position to the base. You can have the base use this position either using the NAVbase position manager or on the LCD screen and buttons directly.

This will give you the absolute position of your base station antenna to <~10 cm geographical accuracy, depending on the proximity of the CORS station to your antenna. Then as long as you always load this position into your base station on power on, instead of letting it average, your rover data will be repeatable to ~2 cm relative accuracy and ~12 cm geographical accuracy.

We tend to say that you loose positional accuracy at around one part per million in terms of distance from base station as an approximate guide, so for every km of distance to the CORS station you loose ~1 cm in accuracy.