Troubleshooting - Sure-Path GPS Boat Lane Tracking

Boat Lane Tracking
Go to content

First determine where there might be a problem.
It is important to understand that GPS signal reception is completely separate from data communication between base and rover and the two need to be looked at separately. Also, GPS reception quality is a variable thing and the signal strength can indicate different problems. Data communication on the other hand is either present or not and it's effects are much easier to see and diagnose and is nearly always down to a phone's internet connectivity. Use the following check list to determine the area to look in:

  • If the Rover status is showing "Invalid" or is showing less than 12 satellites (eg status showing "GPS 7" and not going any higher) then you need to look at the antenna leads for damage or being "pinched" and also the connections at each end. Sometimes the crimping at the connector fails and the connection becomes weak or non existent. This is especially true of the originally supplied RG174 cable going to the white dome style antenna and its TNC style connector.
  • If the Rover status is showing "GPS 12" (ie it is not "DGPS", "RTK Float" or "RTK Fix") then satellite reception is probably OK but no error correction signals are being received from the Base station or from a public NTRIP network. See the next section on Data Communications.
  • If the Rover status is reaching "DGPS" or "RTK Float" then data communication between base and rover is OK but GPS reception, although present, is not good enough to achieve "RTK Fix" mode. The problem could be with the base or rover or both. See the section on GPS Signal Quality.
  • If all the above have been checked but you still can't reach "RTK Fix" mode, then check that the Base station has done a "self survey" in its current location (or has loaded the relevant file if it has been used at another location temporarily). If the base antenna is too far away from where it thinks it is located, then the correction data that the base generates will not be good enough for the rover to achieve RTK Fix.
  • If the Rover status is "RTK Fix" then all is the course and go ski!

Data Communications
If the rover phone is stuck in "GPS" mode and will not achieve "DGPS", "RTK Float" or "RTK Fix" then this means that error signals from the Base are not being received by the Rover.

To find out where the problem is, you must be methodical and follow the path the data takes going from Base to Rover. Do the following in this order:

On the Base phone:
    • Check that the upper progress bar is animating.
      • If there is no animation at all, it is likely that there is no Bluetooth connection and you will have seen another "toast" message to that effect.
      • If there is animation but the hops are small (ie it takes more than 10 hops to cross the screen) then the receiver is not seeing satellites and the likely cause is a problem with the antenna position, the antenna itself or its cable. The most common of these is either the cable being pinched or one of the end connectors has become faulty.
      • If there is animation and it takes less than 10 hops to cross the screen, then all is OK with the Bluetooth connection and the receiver is seeing satellites. Once the receiver has locked on to at least 12 satellites, it should not require more than about 4 or 5 hops for the animation to cross the screen.
    • If the upper progress bar is animating and it is taking less than 10 hops to cross the screen, check that the lower progress bar is also animating. This normally shows that data is successfully being sent to the cloud server. If not, then one of the following could be the cause:
        • The base phone has no internet access. This could be because:
        • There is no WiFi or SIM card installed to enable the phone to have internet access.
          • If there is a SIM card, check that:
            • You have a decent cell signal.
            • Mobile Data is turned on (in the phone's "Settings\Mobile network").
            • The phone's APN settings are correct for your network carrier.
            • You haven't run out of credit!
          • If you are using WiFi, check that:
            • You are still within range of the WiFi
            • The router feeding your WiFi network is still OK and is providing internet access. You can do this by using a browser on a different phone or device on the same WiFi to check whether it has internet access.
        • The Base Phone Mountpoint and/or Password settings are wrong or missing. These are normally pre-configured for you but if you suspect this is a problem, contact us for the correct settings.

If you are seeing both progress bars animating with less than 10 hops to cross the screen, then all is well with the Base receiver and phone and you can move on to checking the Rover.

On the Rover phone:
    • Check that the Mountpoint and Password are set the same as for the Base.
    • Assuming the Rover is using 3/4G for its internet access, do the same checks as for the Base phone:
      • You have a decent cell signal
      • Mobile Data is turned on.
      • The phone's APN settings are correct for your network carrier.
      • You haven't run out of credit!

If the Status on the Rover phone (displayed just below the Connect button) is "DGPS", "RTK Float" or "RTK Fix", then the data link from Base to Rover is fine. If you are only reaching "DGPS" or "RTK Float" and not "RTK Fix", it is not because of the data link. Instead it is to do with the quality/strength of the GPS signals. See the next section.

Another diagnostic is the "Age" value. This displays the elapsed time since the last packet of correction data was received from the Base. Normally it cycles between 0.2 and 3 seconds. If this is happening, then the data links between base and rover are fine. If the Age value starts to climb steadily, then data from the Base is no longer being received. The Rover can still maintain Fix for up to 60 seconds without correction data but after that, it will revert to "GPS" mode. It is not unusual for cell communications to occasionally "pause" for a few seconds and so if Age occasionally climbs to 30 seconds or so, there is no need to worry. However, if it is doing so regularly, then it might be worth examining the system in more detail, particularly if you are "hot spotting" to another phone.

GPS Signal Quality
If the Rover reaches "DGPS" or "RTK Float" but is unable to reach "RTK Fix" status (or "RTK Fix" is unreliable), then the quality of the GPS signal at the Base and/or the Rover needs to be improved.

Base Antenna
We cannot stress enough that if you can get the Base antenna position to be the best it can be, then it is much easier for the Rover to make do with moderate GPS signals and still reach "RTK Fix".

In an ideal world, the base antenna should have clear view of the sky all the way down to about 15⁰ above the horizon in ALL directions. This maximises the number of good satellites that can be used for generating the error data signals the Rover needs to achieve RTK Fix. Also, the antenna should be away from any hard vertical surfaces such as walls of buildings which can give rise to reflected GPS signals which confuse the receivers.

To achieve the above, you may need to mount the antenna high up on a roof or pole so that it is not overlooked by tall trees or buildings. You can run a coax extension to the antenna if it is impractical to have the receiver box and phone close to the antenna. Certainly 30 metre (50') extensions have been tested and you could probably go to 60 metres (100') if required. We would recommend RG58 coax cable for extensions over 3 metres (as opposed to the thinner RG174). When looking for an extension cable, it needs to be SMA-male to SMA-female. Do NOT get anything that has "RP" in the name of the connector such as "RP-SMA-male" as these are "reverse polarity".

Another possible cause of weak GPS signal reception is a damaged or "pinched" antenna lead. The supplied RG174 leads are quite thin and are easily compressed. If this happens, the lead's inate impedance (50 ohms) is changed which can severely reduce the signal strength. If in doubt, switch to the thicker RG58 cable.

Rover Antenna
At the Rover, you are obviously limited to where the antenna can go in the boat but things to be aware of are:

    • If the boat is near a bank with tall trees then they will reduce the GPS signals.
    • If the antenna is mounted too low on the pylon, then you are reducing the antenna's view of the sky.
    • If you are under any sort of roof (eg your jetty canopy), then it will severely restrict GPS signals. When the boat moves out onto open water, it will usually be fine again.
    • The bimini on your boat has very little effect on the GPS. This is because RF signals (such as GPS) are primarily absorbed and stopped by moisture. Trees contain a lot of moisture and therefore are not good. Your bimini hopefully contains zero water and so is fine.

If you find that despite the Base antenna having a very good position, the Rover status is still not reliably in "RTK Fix", then you can upgrade the standard UBlox boat antenna to a survey grade antenna, (the same as is used for the Base).

As mentioned for the Base, check for a damaged or pinched antenna lead. Pinching of the lead can easily happen in the boat as the lead is routed from the pylon to wherever the receiver is being housed, eg under the passenger seat. RG58 cable is significantly more robust than the supplied RG174 cable. It may well be worth considering mounting the receiver and its power supply in a position on the pylon below the antenna, thus negating the need to route the cable very far.

Mapping Accuracy
Sure-Path is indicating that I am driving to the left/right but I am pretty sure this is wrong.

First of all check that you have mapped the course accurately. See Guidelines for Tournament for more information on how to check your course mapping.

If you remap the course, remember to "reselect" the course as the Boat Lane after you have done so as any changes to the survey file are not automatically reflected in the boat lane file.

If all the above is good and you still think you are getting erroneous deviations, then we would respectfully suggest that the system is correct. Remember that every boat is different. Even two boats that are the same year and model will sit in the water differently and will drive differently. The boat should always be balanced. If it is available, set up end-course video and compare the results with Sure-Path. If Sure-Path is consistently telling you that you are left or right on successive passes in both directions, then it is definitely you, since any error in the Sure-Path readings in one direction would give an opposite error in the other direction.

Another consideration to bear in mind is that most drivers use a combination of "distance" viewing and the next guide buoy as their reference points as they drive through the course. The tolerance on the guide buoys is roughly +/- 11cm which is a lot when compared with the tolerance allowed for the boat from the centre line (+/- 20cm). If one guide buoy is say 10cm narrow and the next is 10cm wide of ideal, then although both buoys are "in tolerance", it is extremely difficult to drive a good "straight" line relative to the centre of the boat lane.

Copyright © 2019-23 Post Production Consultants Ltd
Back to content