Here+ RTK & Pixhawk2 3.5 = not precise by meters

Hi all.

I received my Here+ RTK kit w/pixhawk 2.1 and begun testing with latest FW.
First, i updated FW both rover and base, as per instructions (1.30 high precision).
Then i configured base with mission planner, as described in manual. Base precision 2m and survey time 60s. I let settle base for way more than 5 minutes and precision went better than 2m.
connected to drone, it gives “RTK float” into right corner HUD. (sometimes i had also RTK fixed, but for seconds).
then i placed my testbed drone (small F450, logging w/o arming enabled) onto a sidewalk vertex, and then onto another obstacle i can measure distance with, and let him pick some points. Meanwhile, i measured distance from the vertex to the ostacle, which is 11,831 meters.
Finally, i downloaded logs, converted in KML format and loaded into QGIS:

  1. while drone is settling on ground, points are sparse enough to let me think they haven’t centimeter-level precision
  2. measuring distance from first “cluster” of points (sidewalk vertex) to the ostacle, gives 15,5 meter, which is 3 meter off.



  1. you are not injecting the RTCM corrections correctly …
  2. or or Here+ receiver on the drone is picking up too much interference from other transmitters.

I vote on the second one. Raise the GPS receiver a couple of centimeters more above the drone. and re-test.

You must have “RTK fix” in order to get 2cm accuracy. If you do not get that … it just wont give you the precision you want.

Thanks for info.

GPS Antenna is already well over the frame, on a classic gps antenna support (old DJI style) which is around 20cm tall. I get very good reception, meaning 16-18 sats within a minute after powering on.

How can i check if i’m “injecting RTCM correctly”? Also, is there an explanation of the various RTK statuses and their meanings?

What telemetry radio are you using ? How is it configured ?
ECC ? mavlink or RAW ?

I’m using a holybro sik radio kit 433, this one:

configured as it’s “out of the box”, 57600 baud. I didn’t change anything, so it’s default, i don’t know where to change ECC or mvalink vs RAW. If it can help, give me instructions

These setup instructions are not for your GPS, but it does explain how to configure the SiK radio:

We also need to know a bit about the test area you are using. L1 RTK will not likely provide real time cm accuracy unless you have really good conditions such as a big field with limited obstacles.

What coordinates did you use for the base station location and how were they acquired?

To get base coordinates, i followed manual instructions: i connected to base, put the antenna outdoor in open space, wait for fix, survey (60s, 2m precision) let him reach this precision and go “green” light, save home location and “use” it, then connected drone.

i can give you kml file, but pls gime me an email address (i don’t want to make a public post)