SparkFun RTK Facet, inclination angle

GPS/GNSS
1

Hi,

Is it possible to mod the Facet in any way to get inclination angle. Ideally you could give it the pole height and it should provide the GPS coordinates of the tip of the pole.

Any Ideas?

Thanks
Stephen

2

Unfortunately there is not. The RTK Torch has tilt compensation and it requires some tight integration to an IMU specifically designed for GIS applications using the UM980 from Unicore (a different RTK engine than what is in the Facet which is the ZED-F9P from u-blox).

3

Hi Sparky,

Thanks, If the Facet cannot do it, I just wandered if there was an easy way I could attach something to the pole measure pole angle and direction, log it so I could do the calculation offline?

I know how to do the math side, I just need the data (compass direction, and inclination).

Thanks
Stephen

4

If you are confident in your math & pairing time series data the easiest way is to just use SparkFun OpenLog Artemis - DEV-16832 - SparkFun Electronics with a small lipo battery after mounting it at a known distance on the pole (to tip), and performing the IMU calibration (while mounted) OpenLog Artemis Hookup Guide - SparkFun Learn, logging the data to an SD card while also using the facet

…and then integrate/fuse your data on the backend from the 2 SD cards

But I would strongly recommend just getting/using a Torch to make your life easy and avoid all the headaches that come with DIY

You could also use most any 9-Dof IMU + MCU, like SparkFun 9DoF IMU Breakout - ISM330DHCX, MMC5983MA (Qwiic) - SEN-19895 - SparkFun Electronics (parts list Qwiic 9DoF - ISM330DHCX, MMC5983MA Hookup Guide - SparkFun Learn)

5

Sometimes, the more accurate method (verses tilt compensation) is using the field technique of offset points.

A common example is wanting to locate a building corner.
Naturally, next to a building is not a great place to observe GNSS signals from the entire skyline.
We can locate a point that’s projected from one wall that’s offset a known (manually measured) distance, say 20’ for example. You do the same thing for the other wall at that building corner.
Now, the actual location of the building corner can be constructed and all you need is a tape measure.

You can easily expand on this method depending on the accuracy requirements. I’d normally use (2) offset points per wall projection, to accurately establish the direction of my lines that intersect at the true building corner (BC). It only takes a couple seconds per point w/ RTK. No tape measure is required when establishing 2 projected lines with 2 points each. The projected lines intersect at the BC.

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6

Hi Russell,

I think you are correct it’s not worth the hassle for what I want.

The math on the other hand is fantastic, ChatGPT did an amazing job!! I learnt it by trying to nudge my BaseStation position, eg 15cm North, 16cm East and down 14cm and then convert that to the ECEF base values (to align to a local grid). North 1o is a different length to East 1o, and therefor you need to know the ellipsoid you are working with.

Thank very much :slight_smile:
Stephen

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