Loading ...
Sorry, an error occurred while loading the content.

Re: [tracker2] How to deal with GPS drift with OT2?

Expand Messages
  • Jason KG4WSV
    ... how about turning it off? Do you really need to track your car while it s parked for hours on end? -Jason kg4wsv
    Message 1 of 16 , Nov 1, 2009
    • 0 Attachment
      On Sat, Oct 31, 2009 at 5:21 PM, ki6tsf <ki6tsf@...> wrote:
      > Hello,
      >
      > I got a brand new GlobalSat BR-355 SiRF GPS which I use on
      > the secondary port of the OT2.  Unfortunately, I discovered
      > that the position is drifting severely when the car is parked
      > for several hours

      how about turning it off? Do you really need to "track" your car
      while it's parked for hours on end?

      -Jason
      kg4wsv
    • Tom
      Forgive me, but I must inquire: How many feet constitutes drifting severely ? 73, Tom, W3TMC ... From: Jason KG4WSV Subject: Re: [tracker2]
      Message 2 of 16 , Nov 1, 2009
      • 0 Attachment
        Forgive me, but I must inquire:
        How many feet constitutes "drifting severely"?
        73,
        Tom, W3TMC

        --- On Sun, 11/1/09, Jason KG4WSV <kg4wsv@...> wrote:

        From: Jason KG4WSV <kg4wsv@...>
        Subject: Re: [tracker2] How to deal with GPS drift with OT2?
        To: tracker2@yahoogroups.com
        Date: Sunday, November 1, 2009, 10:22 AM

         
        On Sat, Oct 31, 2009 at 5:21 PM, ki6tsf <ki6tsf@arrl. net> wrote:
        > Hello,
        >
        > I got a brand new GlobalSat BR-355 SiRF GPS which I use on
        > the secondary port of the OT2.  Unfortunately, I discovered
        > that the position is drifting severely when the car is parked
        > for several hours

        how about turning it off? Do you really need to "track" your car
        while it's parked for hours on end?

        -Jason
        kg4wsv
      • Tom
        Hello Bernard, Sorry - I replied to one on the subsequent replies to your original question and did not see the information below. (The earlier messages of the
        Message 3 of 16 , Nov 1, 2009
        • 0 Attachment
          Hello Bernard,
          Sorry - I replied to one on the subsequent replies to your original question and did not see the information below.
          (The earlier messages of the thread were in my spam folder - go figure.)
           
          With problems like this, I like to see the signal strength and satellite coverage data from the GPS.
          For a displayless GPS (Is that the case here?) you can use a laptop running a GPS utility like VisualGPS.
          It's free and you can download it from visualgps.net
           
          Remember too that you can have good coverage and a very accurate position at one point in time and then 2 hours later you may see a degradation of position as the GPS acquires different (maybe fewer)  satellites with the rotation of the earth.
           
          best of luck to you,
          Tom, W3TMC
           
           
           
          ----- Original Message -----
          From: ki6tsf
          Sent: Saturday, October 31, 2009 5:21 PM
          Subject: [tracker2] How to deal with GPS drift with OT2?

           

          Hello,

          I got a brand new GlobalSat BR-355 SiRF GPS which I use on
          the secondary port of the OT2. Unfortunately, I discovered
          that the position is drifting severely when the car is parked
          for several hours at the same place (covered or uncovered),
          sometimes up to 300ft. This may be due to reflections.

          I tried with WAAS enabled and disabled,
          and with Static Navigation enabled and disabled and get the
          same problem. Static Navigation is supposed to fix this by
          correcting the coordinates if the calculated position moves
          slower than 1.6 m/s. It does not work: calculated moves
          are grater than that.

          I contacted the manufacturer and they said
          the best option is to have the software deal with it.

          Does anybody sees how to eliminate drift in the OT2?
          So far I was unable to find out how scripting could help.

          Thanks,

          Bernard KI6TSF

        • ki6tsf
          Hello, I posted a pict showing GPS drift at
          Message 4 of 16 , Nov 1, 2009
          • 0 Attachment
            Hello,

            I posted a pict showing GPS drift at http://groups.yahoo.com/group/tracker2/photos/album/411553253/pic/812065518/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

            That's not very nice for a portable or mobile digipeater.

            A Nuvi 350 is occasionally on port A and the GlobalSat BR-355 puck GPS (no display) is permanently connected to port B. The GlobalSat GPS is causing the drift on the picture.

            I tried to set the satellite elevation threshold to a higher value (12 degrees instead of the default value of 5) to eliminate near horizon satellites but that did not help at all. It looks like reflections/multipathing is really bad in some areas and this type of GPS does not deal with them very well.

            Profile 2 is activated when the GPS is at stopped position, with a very low transmit rate (it does that partly because the OT2 is used as a TEMP digi to allow nearby HT's such as VX-8's to get/send APRS messages through it). Profile 1 is activated when the GPS is moving > 8 mph. Since profile switching works well, it would be great if it can be used to decide when to ignore positions because they are likely caused by GPS drift.

            I was wondering if using the AUTOSAVE followed by POSITION X,Y commands when entering Profile 2 would let the OT2 save the last known fix rather than X,Y if X,Y are given special values like 0,0 or illegal values. There doesn't seem to be any way of getting the latest position in scripting. If the above works, the POSITION GPS command should be executed when entering Profile 1 to resume reading the real position.

            Another option would be to use a 2 axis accelerometer to find out when the GPS is physically moving and when it stops but the problem of saving/using the last good fix on the OT2 remains.

            Would it be possible for a script to power on that rogue GPS only after physical motion is detected, and power it off when no motion occured for a certain time? I am not sure how to use the extra I/O pins or the 2-Wire interface from the scripting language of the OT2.
            Would that work?

            Bernard KI6TSF

            --- In tracker2@yahoogroups.com, "Tom" <tmcsail@...> wrote:
            >
            > Hello Bernard,
            > Sorry - I replied to one on the subsequent replies to your original question and did not see the information below.
            > (The earlier messages of the thread were in my spam folder - go figure.)
            >
            > With problems like this, I like to see the signal strength and satellite coverage data from the GPS.
            > For a displayless GPS (Is that the case here?) you can use a laptop running a GPS utility like VisualGPS.
            > It's free and you can download it from visualgps.net
            >
            > Remember too that you can have good coverage and a very accurate position at one point in time and then 2 hours later you may see a degradation of position as the GPS acquires different (maybe fewer) satellites with the rotation of the earth.
            >
            > best of luck to you,
            > Tom, W3TMC
            >
            >
            >
            > ----- Original Message -----
            > From: ki6tsf
            > To: tracker2@yahoogroups.com
            > Sent: Saturday, October 31, 2009 5:21 PM
            > Subject: [tracker2] How to deal with GPS drift with OT2?
            >
            >
            > Hello,
            >
            > I got a brand new GlobalSat BR-355 SiRF GPS which I use on
            > the secondary port of the OT2. Unfortunately, I discovered
            > that the position is drifting severely when the car is parked
            > for several hours at the same place (covered or uncovered),
            > sometimes up to 300ft. This may be due to reflections.
            >
            > I tried with WAAS enabled and disabled,
            > and with Static Navigation enabled and disabled and get the
            > same problem. Static Navigation is supposed to fix this by
            > correcting the coordinates if the calculated position moves
            > slower than 1.6 m/s. It does not work: calculated moves
            > are grater than that.
            >
            > I contacted the manufacturer and they said
            > the best option is to have the software deal with it.
            >
            > Does anybody sees how to eliminate drift in the OT2?
            > So far I was unable to find out how scripting could help.
            >
            > Thanks,
            >
            > Bernard KI6TSF
            >
          • Dan Zubey
            I think one of the things you re going to want is a bit of hysterisis. My T2 is set up to switch from profile 1 to profile 2 when I m going faster than 10mph.
            Message 5 of 16 , Nov 2, 2009
            • 0 Attachment
              I think one of the things you're going to want is a bit of hysterisis.

              My T2 is set up to switch from profile 1 to profile 2 when I'm going
              faster than 10mph. It doesn't switch back until I'm under 1mph.

              What ends up happening is that drift occurs under around 10mph. But
              when you start actually moving faster than 10mph (for real) it'll
              stick in profile 2, until you're completely stopped.

              In practice I think I'd want to raise the value up to about 15 or
              20mph or so if drift were more of a problem.

              -Dan n7nmd

              On Nov 2, 2009, at 0:43, "ki6tsf" <ki6tsf@...> wrote:

              > Hello,
              >
              > I posted a pict showing GPS drift at http://groups.yahoo.com/group/tracker2/photos/album/411553253/pic/812065518/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc
              >
              > That's not very nice for a portable or mobile digipeater.
              >
              > A Nuvi 350 is occasionally on port A and the GlobalSat BR-355 puck
              > GPS (no display) is permanently connected to port B. The GlobalSat
              > GPS is causing the drift on the picture.
              >
              > I tried to set the satellite elevation threshold to a higher value
              > (12 degrees instead of the default value of 5) to eliminate near
              > horizon satellites but that did not help at all. It looks like
              > reflections/multipathing is really bad in some areas and this type
              > of GPS does not deal with them very well.
              >
              > Profile 2 is activated when the GPS is at stopped position, with a
              > very low transmit rate (it does that partly because the OT2 is used
              > as a TEMP digi to allow nearby HT's such as VX-8's to get/send APRS
              > messages through it). Profile 1 is activated when the GPS is moving
              > > 8 mph. Since profile switching works well, it would be great if
              > it can be used to decide when to ignore positions because they are
              > likely caused by GPS drift.
              >
              > I was wondering if using the AUTOSAVE followed by POSITION X,Y
              > commands when entering Profile 2 would let the OT2 save the last
              > known fix rather than X,Y if X,Y are given special values like 0,0
              > or illegal values. There doesn't seem to be any way of getting the
              > latest position in scripting. If the above works, the POSITION GPS
              > command should be executed when entering Profile 1 to resume reading
              > the real position.
              >
              > Another option would be to use a 2 axis accelerometer to find out
              > when the GPS is physically moving and when it stops but the problem
              > of saving/using the last good fix on the OT2 remains.
              >
              > Would it be possible for a script to power on that rogue GPS only
              > after physical motion is detected, and power it off when no motion
              > occured for a certain time? I am not sure how to use the extra I/O
              > pins or the 2-Wire interface from the scripting language of the OT2.
              > Would that work?
              >
              > Bernard KI6TSF
              >
              > --- In tracker2@yahoogroups.com, "Tom" <tmcsail@...> wrote:
              >>
              >> Hello Bernard,
              >> Sorry - I replied to one on the subsequent replies to your original
              >> question and did not see the information below.
              >> (The earlier messages of the thread were in my spam folder - go
              >> figure.)
              >>
              >> With problems like this, I like to see the signal strength and
              >> satellite coverage data from the GPS.
              >> For a displayless GPS (Is that the case here?) you can use a laptop
              >> running a GPS utility like VisualGPS.
              >> It's free and you can download it from visualgps.net
              >>
              >> Remember too that you can have good coverage and a very accurate
              >> position at one point in time and then 2 hours later you may see a
              >> degradation of position as the GPS acquires different (maybe
              >> fewer) satellites with the rotation of the earth.
              >>
              >> best of luck to you,
              >> Tom, W3TMC
              >>
              >>
              >>
              >> ----- Original Message -----
              >> From: ki6tsf
              >> To: tracker2@yahoogroups.com
              >> Sent: Saturday, October 31, 2009 5:21 PM
              >> Subject: [tracker2] How to deal with GPS drift with OT2?
              >>
              >>
              >> Hello,
              >>
              >> I got a brand new GlobalSat BR-355 SiRF GPS which I use on
              >> the secondary port of the OT2. Unfortunately, I discovered
              >> that the position is drifting severely when the car is parked
              >> for several hours at the same place (covered or uncovered),
              >> sometimes up to 300ft. This may be due to reflections.
              >>
              >> I tried with WAAS enabled and disabled,
              >> and with Static Navigation enabled and disabled and get the
              >> same problem. Static Navigation is supposed to fix this by
              >> correcting the coordinates if the calculated position moves
              >> slower than 1.6 m/s. It does not work: calculated moves
              >> are grater than that.
              >>
              >> I contacted the manufacturer and they said
              >> the best option is to have the software deal with it.
              >>
              >> Does anybody sees how to eliminate drift in the OT2?
              >> So far I was unable to find out how scripting could help.
              >>
              >> Thanks,
              >>
              >> Bernard KI6TSF
              >>
              >
              >
              >
              >
              > ------------------------------------
              >
              > Yahoo! Groups Links
              >
              >
              >
            • Keith VE7GDH
              Bernard KI6TSF wrote... ... Why would it drift more when parked compared to mobile? Hopefully you are using SmartBeaconing and have it backed off to
              Message 6 of 16 , Nov 2, 2009
              • 0 Attachment
                Bernard KI6TSF wrote...

                > I got a brand new GlobalSat BR-355 SiRF GPS which I use on
                > the secondary port of the OT2. Unfortunately, I discovered
                > that the position is drifting severely when the car is parked
                > for several hours at the same place (covered or uncovered),
                > sometimes up to 300ft. This may be due to reflections.

                Why would it "drift" more when parked compared to mobile? Hopefully you
                are using SmartBeaconing and have it backed off to something like 10-30
                minutes for the slow rate if you are going to leave it on all the time.
                I use 10 minutes for the slow rate in SmartBeaconing, but then again,
                it's turned off when parked.

                I too would be curious too about the accuracy of the GPS receiver. Take
                the OT2 right out of the picture. Connect the GPS to a computer and
                watch it in something like VisualGPS to see what is going on. You could
                of course just view the NMEA strings in a terminal program, but
                VisualGPS is a freebie download and I know there are other programs that
                do the same thing. Do you see your position wandering everywhere, or
                just when you are parked in one particular spot? There could be
                something interfering with the GPS receiver.
                www.visualgps.net/VisualGPS/

                > I tried with WAAS enabled and disabled, and with Static Navigation
                > enabled and disabled and get the same problem. Static Navigation is
                > supposed to fix this by correcting the coordinates if the calculated
                > position moves slower than 1.6 m/s. It does not work: calculated
                > moves are grater than that.

                What do you mean by "Static Navigation"? Do you mean entering a fixed
                position into the OT2 rather than getting the position from the GPS? If
                you enter a fixed position, the position shouldn't change at all. Or is
                this some setting in that particular GPS receiver?

                73 es cul - Keith VE7GDH
                --
                "I may be lost, but I know exactly where I am!"
              • Fred Hillhouse
                I got a brand new GlobalSat BR-355 SiRF GPS which I use on the secondary port of the OT2. Unfortunately, I discovered that the position is drifting severely
                Message 7 of 16 , Nov 2, 2009
                • 0 Attachment
                  I got a brand new GlobalSat BR-355 SiRF GPS which I use on
                  the secondary port of the OT2. Unfortunately, I discovered
                  that the position is drifting severely when the car is parked
                  for several hours at the same place (covered or uncovered),
                  sometimes up to 300ft. This may be due to reflections.
                   
                  This is a common. The satellites are always moving in the constellation. I wonder if your receiver is more sensitive than mine. Or does mine have more filtering to keep from ping-ponging me around. Covered is usually not a good place place to park for a GPS, especially if it is a metal cover. Any signal it receives will be either from low on the horizon or reflecting from some other surface. Judging by the overhead view, your view to the horizon is blocked.
                   
                  I tried with WAAS enabled and disabled, 
                   
                  This will only matter if you can actually see the WAAS satellites. They are geo-stationary which means they are lower in the sky (New England anyway). Building, trees will attenuate then quite a bit. BTW, with software packages like Orbitron you can see where in the sky the WAAS satellites are as well as the regular constellation.
                   
                  I found this to be an interesting and educational read.
                   
                   
                  and with Static Navigation enabled and disabled and get the
                  same problem. Static Navigation is supposed to fix this by
                  correcting the coordinates if the calculated position moves
                  slower than 1.6 m/s. It does not work: calculated moves
                  are grater than that. 
                   
                  If the GPS is turned off then the last valid location will be remembered as used. However, turning the GPS off means that there is a delay until the unit reacquires. A relay breaking the GPS TX line to the T2 might serve well. I have not tried that but it may work for you.

                  I contacted the manufacturer and they said
                  the best option is to have the software deal with it. 
                   
                  That is true in regards to their GPS. Some units do some filtering, some do none. Yours apparently does none and may be more sensitive as well.

                  Does anybody sees how to eliminate drift in the OT2?
                   
                  I saw other answers like increasing your slow speed. That is a good direction to try.
                   
                   
                  Best regards,
                  Fred
                • Bob Poortinga
                  ... He is probably referring to the Static Navigation option that can be configured for SiRF III GPSs by using the SiRFdemo software. I wonder if Bernard has
                  Message 8 of 16 , Nov 2, 2009
                  • 0 Attachment
                    "Keith VE7GDH" <ve7gdh@...> writes:

                    > What do you mean by "Static Navigation"?

                    He is probably referring to the "Static Navigation" option that can be
                    configured for SiRF III GPSs by using the SiRFdemo software.

                    I wonder if Bernard has tried "Track Smoothing" or increasing the acceptable
                    minimum signal satellite strength and turning off degraded mode and dead
                    reckoning?

                    --
                    Bob Poortinga K9SQL <http://www.linkedin.com/in/bobpoortinga>
                    Bloomington, Indiana US
                  • Scott Miller
                    ... If you have AUTOSAVE on in profile 2, you can set profile 2 to BMODE FLOW, or anything but AUTO, and it ll lose GPS lock and save the last position.
                    Message 9 of 16 , Nov 2, 2009
                    • 0 Attachment
                      > I was wondering if using the AUTOSAVE followed by POSITION X,Y commands
                      > when entering Profile 2 would let the OT2 save the last known fix rather
                      > than X,Y if X,Y are given special values like 0,0 or illegal values.

                      If you have AUTOSAVE on in profile 2, you can set profile 2 to BMODE
                      FLOW, or anything but AUTO, and it'll 'lose' GPS lock and save the last
                      position.

                      Scott
                    • James Ewen
                      ... Take a look at your surroundings... If you park the car nose in, you ve got a wall and car port with a roof that looks to be at least 9 feet high right in
                      Message 10 of 16 , Nov 2, 2009
                      • 0 Attachment
                        On Mon, Nov 2, 2009 at 1:43 AM, ki6tsf <ki6tsf@...> wrote:

                        > I posted a pict showing GPS drift at http://groups.yahoo.com/group
                        > /tracker2/photos/album/411553253/pic/812065518/view?picmode=
                        >&mode=tn&order=ordinal&start=1&count=20&dir=asc
                        >
                        > That's not very nice for a portable or mobile digipeater.

                        Take a look at your surroundings... If you park the car nose in,
                        you've got a wall and car port with a roof that looks to be at least 9
                        feet high right in front of the car. Behind you is a 3 storey
                        building, maybe 30 feet away. At least you didn't park under the tree.
                        (Gotta love Google Streetview!)

                        You'll have blocked views of the horizon for most of the azimuth
                        around you. The 3 storey wall behind you will probably bounce signals
                        like crazy, leading to position accuracy problems with the GPS.

                        If you put a relay in the data line between the GPS and the OT2,
                        triggered by the accessory line in the vehicle, you will basically
                        disconnect the GPS from the OT2. Configure the OT2 to use the last
                        known position. Leave the GPS power on constant 12 volts, and the GPS
                        will always be active, leading to faster position acquisition when you
                        start the vehicle. (By faster, I mean instantaneous, unless you have
                        parked in an underground or covered parking area)

                        James
                        VE6SRV
                      • ki6tsf
                        Hello, Thank you to all who replied and for all the suggestions! Yes, Static Navigation is a feature built-in in SiRF III-based GPSs and I used SiRFDemo to set
                        Message 11 of 16 , Nov 2, 2009
                        • 0 Attachment
                          Hello,

                          Thank you to all who replied and for all the suggestions!

                          Yes, Static Navigation is a feature built-in in SiRF III-based
                          GPSs and I used SiRFDemo to set it. It is supposed to eliminate
                          drift. I'll check with SiRF directly if they can advise how
                          to tune it.

                          Actually yes, I enabled Track Smoothing too and that didn't help.
                          I have not raised the satellite signal strenght threshold, this is
                          next on my checklist.

                          I set degraded mode and dead reckoning on (I found it really cool
                          to have a GPS receiver that supports those modes!!!). I'll have
                          to try with these features turned off.

                          Anyways I hope a combination of all or some of the suggestions
                          received on this newsgroup will solve that drift problem!

                          Thanks to all,

                          Bernard KI6TSF

                          --- In tracker2@yahoogroups.com, Bob Poortinga <bobp+yahoo@...> wrote:
                          >
                          > "Keith VE7GDH" <ve7gdh@...> writes:
                          >
                          > > What do you mean by "Static Navigation"?
                          >
                          > He is probably referring to the "Static Navigation" option that can be
                          > configured for SiRF III GPSs by using the SiRFdemo software.
                          >
                          > I wonder if Bernard has tried "Track Smoothing" or increasing the acceptable
                          > minimum signal satellite strength and turning off degraded mode and dead
                          > reckoning?
                          >
                          > --
                          > Bob Poortinga K9SQL <http://www.linkedin.com/in/bobpoortinga>
                          > Bloomington, Indiana US
                          >
                        • k7ybz
                          When I originally read your post I was thinking unit sensitivity of the BR-355 compared to Garmin pucks. I had remembered reading the sensitivity of the BR-355
                          Message 12 of 16 , Nov 2, 2009
                          • 0 Attachment
                            When I originally read your post I was thinking unit sensitivity of the BR-355 compared to Garmin pucks. I had remembered reading the sensitivity of the BR-355 as being around -160 and Garmin around -185.
                            Then I went back and looked at the specs again and noticed Garmin specifies their sensitivity as dBW and everyone else specifies it in dBm. There in lies the difference (and another Garmin marketing ploy): 0dBW = +30dBm.

                            Ahhh, the numbers game!

                            I may have missed where the puck was placed, but the puck is much better off on the roof of the vehicle than on the dash. On some units, the magnet can be removed and mounted directly to a surface. I did not investigate this for your particular unit though.

                            Larry
                            K7YBZ

                            --- In tracker2@yahoogroups.com, "ki6tsf" <ki6tsf@...> wrote:
                            >
                            > Hello,
                            >
                            > Thank you to all who replied and for all the suggestions!
                            >
                            > Yes, Static Navigation is a feature built-in in SiRF III-based
                            > GPSs and I used SiRFDemo to set it. It is supposed to eliminate
                            > drift. I'll check with SiRF directly if they can advise how
                            > to tune it.
                            >
                            > Actually yes, I enabled Track Smoothing too and that didn't help.
                            > I have not raised the satellite signal strenght threshold, this is
                            > next on my checklist.
                            >
                            > I set degraded mode and dead reckoning on (I found it really cool
                            > to have a GPS receiver that supports those modes!!!). I'll have
                            > to try with these features turned off.
                            >
                            > Anyways I hope a combination of all or some of the suggestions
                            > received on this newsgroup will solve that drift problem!
                            >
                            > Thanks to all,
                            >
                            > Bernard KI6TSF
                            >
                            > --- In tracker2@yahoogroups.com, Bob Poortinga <bobp+yahoo@> wrote:
                            > >
                            > > "Keith VE7GDH" <ve7gdh@> writes:
                            > >
                            > > > What do you mean by "Static Navigation"?
                            > >
                            > > He is probably referring to the "Static Navigation" option that can be
                            > > configured for SiRF III GPSs by using the SiRFdemo software.
                            > >
                            > > I wonder if Bernard has tried "Track Smoothing" or increasing the acceptable
                            > > minimum signal satellite strength and turning off degraded mode and dead
                            > > reckoning?
                            > >
                            > > --
                            > > Bob Poortinga K9SQL <http://www.linkedin.com/in/bobpoortinga>
                            > > Bloomington, Indiana US
                            > >
                            >
                          Your message has been successfully submitted and would be delivered to recipients shortly.