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Re: [aprsisce] Position Ambiguity

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  • James Ewen
    ... This to me is a strange mindset. You are basically saying I m only going to implement a subset of the APRS specification, the parts that make sense to me.
    Message 1 of 20 , Jan 1, 2011
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      On Sat, Jan 1, 2011 at 9:19 AM, Lynn W Deffenbaugh (Mr) <kj4erj@...> wrote:

      > Not yet.  I'm still not totally convinced as to the utility or
      > usefulness of ambiguity and it seems to always raise the question of
      > "it's not showing me where I really am".  I'll add it to the list to
      > support in some future revision.

      This to me is a strange mindset. You are basically saying I'm only
      going to implement a subset of the APRS specification, the parts that
      make sense to me.

      Obviously there's no way to be able to make a program support every
      single aspect of APRS from the start unless you sit on it under
      development until it is perfect, then release it. Obviously we're
      playing with the program as it is growing, and we get access to new
      features as they are added. We suggest features desired, and wait for
      them to bubble to the top of the queue.

      Position ambiguity would seem to be a fairly simple feature to
      implement. I'd hang it in the menu structure in the Precision section
      where you have the !DAO! feature. Of course that now brings up the
      query... if you don't see the usefulness of ambiguity, why have the
      ability to disable 2 digits of !DAO! precision? If you can resolve a
      position accurately to give the extra precision that !DAO! extensions
      give, then why have the ability to shut it off?

      Obviously I'm playing the Devil's Advocate here, just trying to show
      the other side of the coin.

      One thing that I love is that you draw the purple circle around the
      received stations that have ambiguous positions. I don't know of
      anyone else highlighting ambiguous position reports. That's the
      biggest problem with position ambiguity... it's not that people use
      it, but rather that receiving stations ignore position ambiguity, and
      add digits of precision which are inaccurate, and then depict the
      inaccurate location to the end user as if it were a high precision
      location report.

      I sent a feature request in to Hessu at aprs.fi yesterday suggesting a
      method of indicating position ambiguity on the site. I like your tight
      purple circle idea, which highlights the station as transmitting an
      ambiguous position. I'd put the station at midrange values rather than
      padding out with zeros so as to minimize the amount of possible
      maximum displacement. Then I would highlight the rectangle of possible
      locations where the station would be, rather than draw a circle.

      When zero padding, the icon ends up on one vertex of the rectangle of
      possible locations. Drawing a circle at that location then puts 3/4 of
      the circle outside of the area where the station could possibly be,
      which again is adding to the depicted inaccuracy.

      Having the ambiguous station icon drawn at the center of the ambiguity
      rectangle with a tight purple circle around it, and then when zoomed
      out far enough being surrounded by a rectangle showing the bounds of
      the ambiguity area would be the 100% best solution in my mind. This
      would alert the observer to the fact that the station is somewhere
      within the bounds of that rectangle.

      Obviously if one were to select position ambiguity in APRSISCS/32, the
      program should draw the area of ambiguity around the user's location
      so the user realizes that they are transmitting lower precision
      location information. That would actually look interesting while
      driving around... rectangles would highlight as you drive from one to
      the next.

      Just my 2 bits...

      James
      VE6SRV
    • g4ilo
      ... To save 4 characters in the length of a packet transmitting a position with unnecessary accuracy? I think I was with Lynn in that if I m bothered about
      Message 2 of 20 , Jan 1, 2011
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        --- In aprsisce@yahoogroups.com, James Ewen <ve6srv@...> wrote:
        >
        > query... if you don't see the usefulness of ambiguity, why have the
        > ability to disable 2 digits of !DAO! precision? If you can resolve a
        > position accurately to give the extra precision that !DAO! extensions
        > give, then why have the ability to shut it off?

        To save 4 characters in the length of a packet transmitting a position with unnecessary accuracy?

        I think I was with Lynn in that if I'm bothered about people knowing exactly where I am then I wouldn't be doing APRS at all. However, I can see an argument that APRS is not just about showing one's exact position, but the system still needs to know the general area you are in to determine what information is relevant to you or what area anything you originate is relevant to. So if someone wants to participate in APRS without having their station pinpointed on a map positoin ambiguity makes some kind of sense.

        Julian, G4ILO
      • Lynn W Deffenbaugh (Mr)
        ... Ok, finally a justification that I can understand and appreciate. Question is, how many people will really set and unset Ambiguity for that purpose? And
        Message 3 of 20 , Jan 1, 2011
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          ka0azs wrote:
          > A couple of reasons for ambiguity:
          >
          > 1. You don't have a GPS and are manually entering your coordinates. Ambiguity allows you to accurately show the limitations of the source of your position. Example, walking around a hamfest with a D7 and no functioning GPS. Rather that mislead folks into thinking you are in a particular place, just that you are somewhere in the confines of the fest (and hopefully have a contact frequency in your status.
          >
          > To put in a more defined position would be inaccurate and misleading. Probably not a big deal for most folks, but for those of us that spent years dealing with differences between accuracy and precision, it can be a bit annoying.
          >

          Ok, finally a justification that I can understand and appreciate.
          Question is, how many people will really set and unset Ambiguity for
          that purpose? And with APRSISCE (the most popular mobile use), they're
          probably running a real GPS and direct APRS-IS connection, so they're
          probably not approximating their position anyway.

          > 2. Yes, security (at least as perceived by non-hams) can be an issue.
          >
          > I once helped with the configuration of a digipeater. The site owners had no problem with the transmitter and antenna, just didn't want their site "highlighted" on maps.
          >

          It was somehow a disguised tower? This is exactly the kind of thinking
          that makes absolutely no sense to me.

          > To keep them happy we offset the transmitted position and gave it about 1/2 mile position ambiguity. That put the actual digi site in the circle, but did not "highlight" it. If you tried to DF the site, you'd end up in the approximate area, but to try to refine it, if you started at the center of the circle, you'd be in a area that happened to be covered by the department a fellow ham worked as a dispatcher for. :-)
          >

          I haven't done any foxhunting or DFing, but I thought the general idea
          was to start away from the target and triangulate a bearing from
          multiple positions decidedly distant from the target?

          > Security concerns overblown? Probably, but it was their property and they didn't have to let us put a digi there. By doing the ambiguous position, we answered their concerns and sidestepped a possible roadblock to putting up a needed digi.
          >

          Agreed, and such a site was probably a TNC beaconing a static beacon?
          Just guessing and trying to learn, not challenging or being obstinate
          (although it sure reads that way to me). Questions stimulate discussion
          and with discussion comes learning and understanding. Bold-faced
          statements of "you need to do this because it's there", doesn't do much
          to help me appreciate the "why"s.

          > Both minor to me, but I'd like this eventually, if nothing else to help cement APRSIS as THE new APRS client!
          >
          > As far as "it's not showing me where I really am", just make it a non-default option. Of course we could also do a little education on the fact "where I really am" depends on a lot more factors than where your GPS display says you are.;-)
          >

          That's why it's on the ToDo list (now). It'll come eventually because I
          really do want to cover at least aprs101.pdf completely. The remainder
          of the 1.1 and 1.2 specs are a bit more nebulous, but are also in my
          viewfinder.

          Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32


          > 73 Randy KA0AZS
          >
          > --- In aprsisce@yahoogroups.com, "Lynn W Deffenbaugh (Mr)" <kj4erj@...> wrote:
          >
          >
          >> Not yet. I'm still not totally convinced as to the utility or
          >> usefulness of ambiguity and it seems to always raise the question >of "it's not showing me where I really am".
          >>
          >
          >
          >
          >
          >
          > ------------------------------------
          >
          > Yahoo! Groups Links
          >
          >
          >
          >
          >
        • Jordan Hayes KG6UAE
          ... So you don t understand and appreciate the WinLink idea of publishing grid-square for a system, where the area that it serves is more important than
          Message 4 of 20 , Jan 1, 2011
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            > Ok, finally a justification that I can understand and appreciate.

            So you don't understand and appreciate the WinLink idea of publishing
            grid-square for a system, where the area that it serves is more
            important than exactly where it's located?

            /jordan KG6UAE
          • Lynn W Deffenbaugh (Mr)
            ... I do have it on the ToDo list. I asked the question so I could understand the use of such a function as well as to get an idea of what priority to assign
            Message 5 of 20 , Jan 1, 2011
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              James Ewen wrote:
              > On Sat, Jan 1, 2011 at 9:19 AM, Lynn W Deffenbaugh (Mr) <kj4erj@...> wrote:
              >
              >
              >> Not yet. I'm still not totally convinced as to the utility or
              >> usefulness of ambiguity and it seems to always raise the question of
              >> "it's not showing me where I really am". I'll add it to the list to
              >> support in some future revision.
              >>
              >
              > This to me is a strange mindset. You are basically saying I'm only
              > going to implement a subset of the APRS specification, the parts that
              > make sense to me.
              >

              I do have it on the ToDo list. I asked the question so I could
              understand the use of such a function as well as to get an idea of what
              priority to assign to it. I plan to support all of aprs101.pdf and as
              much of the 1.1 and 1.2 addendums as I can find specific documentation
              (and usefulness) for.

              > Obviously there's no way to be able to make a program support every
              > single aspect of APRS from the start unless you sit on it under
              > development until it is perfect, then release it. Obviously we're
              > playing with the program as it is growing, and we get access to new
              > features as they are added. We suggest features desired, and wait for
              > them to bubble to the top of the queue.
              >
              > Position ambiguity would seem to be a fairly simple feature to
              > implement. I'd hang it in the menu structure in the Precision section
              > where you have the !DAO! feature. Of course that now brings up the
              > query... if you don't see the usefulness of ambiguity, why have the
              > ability to disable 2 digits of !DAO! precision? If you can resolve a
              > position accurately to give the extra precision that !DAO! extensions
              > give, then why have the ability to shut it off?
              >

              Every feature is "easy" to implement. But if you've got a thousand
              small rocks to move, it still requires a substantial amount of time to
              move them all.

              > Obviously I'm playing the Devil's Advocate here, just trying to show
              > the other side of the coin.
              >

              I appreciate the conversation, truly.

              > One thing that I love is that you draw the purple circle around the
              > received stations that have ambiguous positions. I don't know of
              > anyone else highlighting ambiguous position reports. That's the
              > biggest problem with position ambiguity... it's not that people use
              > it, but rather that receiving stations ignore position ambiguity, and
              > add digits of precision which are inaccurate, and then depict the
              > inaccurate location to the end user as if it were a high precision
              > location report.
              >

              The purple circle was done in self-defense a while back when I received
              complaints about a station that "wasn't showing the proper location on
              the map". It took a few days of research before I finally noticed the
              ambiguous position that the station was transmitting. So, now there's a
              way to highlight it on the map and it shows in the station popup dialog.

              > I sent a feature request in to Hessu at aprs.fi yesterday suggesting a
              > method of indicating position ambiguity on the site. I like your tight
              > purple circle idea, which highlights the station as transmitting an
              > ambiguous position. I'd put the station at midrange values rather than
              > padding out with zeros so as to minimize the amount of possible
              > maximum displacement. Then I would highlight the rectangle of possible
              > locations where the station would be, rather than draw a circle.
              >
              > When zero padding, the icon ends up on one vertex of the rectangle of
              > possible locations. Drawing a circle at that location then puts 3/4 of
              > the circle outside of the area where the station could possibly be,
              > which again is adding to the depicted inaccuracy.
              >

              My circle is actually centered by filling in 1/2 of the missing digit.
              If it is bb.bbb, I draw it at 30.00. If it is xb.bbb, it ends up at
              x5.000. xx.bbb is xx.500 and so forth.

              > Having the ambiguous station icon drawn at the center of the ambiguity
              > rectangle with a tight purple circle around it, and then when zoomed
              > out far enough being surrounded by a rectangle showing the bounds of
              > the ambiguity area would be the 100% best solution in my mind. This
              > would alert the observer to the fact that the station is somewhere
              > within the bounds of that rectangle.
              >

              I considered a rectangle, but the circle looked cooler. And for the
              purists, they can just square up the area with their eye.
              > Obviously if one were to select position ambiguity in APRSISCS/32, the
              > program should draw the area of ambiguity around the user's location
              > so the user realizes that they are transmitting lower precision
              > location information. That would actually look interesting while
              > driving around... rectangles would highlight as you drive from one to
              > the next.
              >

              Interesting idea, but I'm still probably going to insist on Me being at
              the best known actual coordinate. However, there's another ToDo item
              that will show the last point at which a beacon was transmitted, and
              possibly also show the last point where a digipeat was heard. The last
              transmission point would be a good place to show the ambiguity. Even
              for a non-moving station, it could then be offset by up to 1/2 the
              ambiguity (or something like that...).

              > Just my 2 bits...
              >

              As long as you're not looking for change! <grin>

              Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

              > James
              > VE6SRV
              >
            • h0chus_p0ckus
              Maybe we could come up with a different visual representation for stations with ambiguity set? Circle of ambiguity is I believe the phrase used. The
              Message 6 of 20 , Jan 1, 2011
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                "Maybe we could come up with a different visual representation for
                stations with ambiguity set?"

                "Circle of ambiguity" is I believe the phrase used. The conventional graphic representation when you are unsure of the position, is to use a shaded circle which is solid at the center (the reported or probable position) and fades out toward the edges of the probable position. You'll see this used in cell phone mapping applications, where the position may be 'exact' from a GPS, or somewhat less exact from a SkyHook assist, or really uncertain, from a cell phone tower triangulation. The "certain" position is a spot, the less exact one a shaded circle, the least certain one a much larger shaded circle.

                The answer is already out there, the rest is just a simple exercise in programming. (Sorry, Lynn!<G>)

                --Red
              • ka0azs
                One reason is to show that there is a digi in that area. Helps with event planning (do I need to dig up a portable digi and all the work set up for a temporary
                Message 7 of 20 , Jan 1, 2011
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                  One reason is to show that there is a digi in that area.

                  Helps with event planning (do I need to dig up a portable digi and all the work set up for a temporary set up entails?)when you know there is coverage in your area of interest. Particularly when setting up support in area you don't frequent on a daily basis.

                  And, quite frankly, I didn't even consider the possibility of NOT putting a position in. Never occurred to me.

                  I'd have to go back and look at my notes (if I can find them, been almost 10 years), but we were doing this with a burned EPROM, and I'm not sure if the configuration file let you do "no position", or if it would have simply broadcast a position of 0.00 by 0.00.

                  73

                  Randy KA0AZS
                  --- In aprsisce@yahoogroups.com, Rob Giuliano <kb8rco@...> wrote:
                  >
                  > Why do you need to have the digi provide its position at all?
                  > I realize that information is a valuable part of the system, but if it means no digi vs digi, is it a must?
                  >  
                  >  
                  > It has to ID, but I don't think it "must provide" its position.  At APRS.fi and such, it might be hard to follow, but the diretive of getting the data  across the "dead spot" would still be accomplished.
                  >
                  > Robert Giuliano
                  > KB8RCO
                  >
                • ka0azs
                  ... I would find it useful at public service events where I m setting up a portable station with no GPS and limited time frame to fool around with it. Of
                  Message 8 of 20 , Jan 1, 2011
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                    --- In aprsisce@yahoogroups.com, "Lynn W Deffenbaugh (Mr)" <kj4erj@...> wrote:
                    >

                    >
                    > Ok, finally a justification that I can understand and appreciate.
                    > Question is, how many people will really set and unset Ambiguity >for that purpose? And with APRSISCE (the most popular mobile use), >they're probably running a real GPS and direct APRS-IS connection, >so they're probably not approximating their position anyway.

                    I would find it useful at public service events where I'm setting up a portable station with no GPS and limited time frame to fool around with it. Of course, the APRSIS32 version of using the map and cross-hairs to set a position might make that obsolete.

                    I'll have to play with it over the next year as I support PSEs. In the past the position was entered manually with coords from the nearest available GPS (sometimes passed by voice from a nearby vehicle) or pulled from a map. I'm not sure about +SA, but IIRC DOS automatically kicked in and calculated the ambiguity based on number of significant digits in the coordinates.

                    As I've stated before, I'm very RF centric. Don't have any phone that will support the CE version, no plans to get one in the near future, refuse to pay for dataplans (I only have a cell because work requires it and family insists). And, as I consider PSEs training for emergency operations, I always assume the internet will NOT be available when I need it, hence I play with the IS parts only as an afterthought.

                    > It was somehow a disguised tower? This is exactly the kind of >thinking that makes absolutely no sense to me.

                    Wasn't a radio tower. A very tall building with some sensitive types working in there (as in their activities were considered sensitive, not that they got hurt feelings easily). I think it was also a bit of "we're willing to do it for you, but we don't want everyone up here asking for space".

                    > I haven't done any foxhunting or DFing, but I thought the general >idea was to start away from the target and triangulate a bearing >from multiple positions decidedly distant from the target?

                    Not an expert, but by my understanding, DFing the signal (which would be fun, isolating that one transmitter on 144.39) from a distance would resolve it into a position fix approximately the same size of the ambiguity circle. Moving into that area (not all of which is accessible to the public) to further localize it would attract the attention of several folks, the nicest of which would be our friend in Dispatch. Probably over thinking it, most folks would look at the transmitted position and call it good. but it made the site owners happy.

                    >...and such a site was probably a TNC beacon a static beacon?

                    Yep. AEA with the config file burned into an EPROM

                    > Just guessing and trying to learn, not challenging or being >obstinate (although it sure reads that way to me).

                    Not to me. If nothing else these type of questions might help me handle a similar situation in the future with a better approach

                    >Questions stimulate discussion and with discussion comes learning >and understanding.

                    Absolutely

                    73

                    Randy KA0AZS
                  • Lynn W Deffenbaugh (Mr)
                    WinLink s grid-square system doesn t show up in APRS. Something somewhere WINLINK is injecting 0.1nm abiguity position packets into APRS-IS for the
                    Message 9 of 20 , Jan 1, 2011
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                      WinLink's "grid-square system" doesn't show up in APRS. Something
                      somewhere "WINLINK" is injecting 0.1nm abiguity position packets into
                      APRS-IS for the WinLink stations These packets specify a lat/lon, not a
                      gridsquare, so the distinction is lost in the translation. (See
                      http://aprs.fi/?c=raw&call=WINLINK&limit=50&view=normal) I can only
                      understand and appreciate things that I can see in the lens through
                      which I view the world (APRS-IS).

                      Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

                      Jordan Hayes KG6UAE wrote:
                      >> Ok, finally a justification that I can understand and appreciate.
                      >>
                      >
                      > So you don't understand and appreciate the WinLink idea of publishing
                      > grid-square for a system, where the area that it serves is more
                      > important than exactly where it's located?
                      >
                      > /jordan KG6UAE
                      >
                    • Jordan Hayes KG6UAE
                      ... I think you re being obtuse. ... I think the lat/lon is the center-point of the grid-square in this case. Since APRS doesn t know from grid-square, that s
                      Message 10 of 20 , Jan 1, 2011
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                        Lynn writes:

                        > WinLink's "grid-square system" doesn't show up in APRS.

                        I think you're being obtuse.

                        > Something somewhere "WINLINK" is injecting 0.1nm abiguity position
                        > packets into APRS-IS for the WinLink stations These packets specify
                        > a lat/lon, not a gridsquare, so the distinction is lost in the
                        > translation.

                        I think the lat/lon is the center-point of the grid-square in this case.
                        Since APRS doesn't know from grid-square, that's the best the WinLink
                        folks could do. My point is that the lat/lon of those stations should
                        probably not be represented on the screen in the same way as a tracker
                        with 6-digits of accuracy are represented.

                        > I can only understand and appreciate things that I can see
                        > in the lens through which I view the world (APRS-IS).

                        Yes, this is exactly what I am asking you to do: see the world through
                        the lens of APRS and see that a different representation of ambiguous
                        positions be used in APRS.

                        You said earlier that you don't understand or appreciate it. You're not
                        trying hard enough.

                        Sheesh,

                        /jordan KG6UAE
                      • James Ewen
                        ... More likely circle of probability is more likely. ... Yes, that would be a way to represent a possible location. However in APRS terms, the ambiguity is
                        Message 11 of 20 , Jan 1, 2011
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                          On Sat, Jan 1, 2011 at 12:53 PM, h0chus_p0ckus <reply.via.list@...> wrote:

                          >  "Circle of ambiguity" is I believe the phrase used.

                          More likely circle of probability is more likely.

                          > The conventional graphic representation when you are unsure
                          > of the position, is to use a shaded circle which is solid at the center
                          > (the reported or probable position) and fades out toward the edges of
                          > the probable position.

                          Yes, that would be a way to represent a possible location. However in
                          APRS terms, the ambiguity is defined by dropping digits of precision,
                          and because the location is described by using lat/long pairs, as you
                          drop digits of precision, you create rectangles of probability, with
                          the probability of being at any location within that rectangle being
                          uniform throughout the rectangle.

                          If you were to use shading to represent the possibility of the station
                          being at any one point in the rectangle, where the opacity of the
                          shading represents the possibility of the station being at that
                          location, you would need to use uniform opacity throughout the
                          rectangle.

                          Using a circle misrepresents the area of possibility, and using a
                          fading pattern within the circle could be interpreted to represent
                          that the location suggested is somehow of higher probability of being
                          the actual location than other areas within the shaded area.

                          Having any type of indication of stations sending ambiguous reports is
                          better than nothing, but if you are going to try representing
                          something, it is better to do it right than to go through multiple
                          iterations of incorrect representations, and having to explain to
                          people why:

                          a) the circle around the icon that is plotted doesn't include the
                          actual location they are at, or
                          b) the shading where they actually are located is lighter than near
                          the icon, when they know there's better probability of finding them
                          further away from the icon location.

                          I'm all about accuracy, even when it includes imprecise information.
                          Accuracy in my world is far more important than precision.

                          James
                          VE6SRV
                        • James Ewen
                          ... That is incorrect... there are a number of cases where APRS packets can include Maidenhead grid square information. James VE6SRV
                          Message 12 of 20 , Jan 1, 2011
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                            On Sat, Jan 1, 2011 at 2:30 PM, Jordan Hayes KG6UAE <kg6uae@...> wrote:

                            > Since APRS doesn't know from grid-square,

                            That is incorrect... there are a number of cases where APRS packets
                            can include Maidenhead grid square information.

                            James
                            VE6SRV
                          • Lynn W Deffenbaugh (Mr)
                            ... I believe he was referring to my comment that the GridSquares known to WinLink were not being used in the APRS-IS packets transmitting the ambiguous
                            Message 13 of 20 , Jan 1, 2011
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                              James Ewen wrote:
                              > On Sat, Jan 1, 2011 at 2:30 PM, Jordan Hayes KG6UAE <kg6uae@...> wrote:
                              >
                              >
                              >> Since APRS doesn't know from grid-square,
                              >>
                              >
                              > That is incorrect... there are a number of cases where APRS packets
                              > can include Maidenhead grid square information.
                              >

                              I believe he was referring to my comment that the GridSquares known to
                              WinLink were not being used in the APRS-IS packets transmitting the
                              ambiguous location of the same station.

                              And, IIRC, there's only one non-deprecated use of GridSquares as a
                              location in APRS. Correction 2. From page 25 (35) of aprs101.pdf.

                              An alternative method of expressing a station’s location is to provide a
                              Maidenhead locator (grid square). There are four ways of doing this:

                              • In a Status Report — e.g. IO91SX/- (/- represents the symbol for a
                              “house”).
                              • In Mic-E Status Text — e.g. IO91SX/G (/G indicates a “grid square”).
                              • In the Destination Address — e.g. IO91SX. (obsolete).
                              • In AX.25 beacon text, with the [ APRS Data Type Identifier — e.g.
                              [IO91SX] (obsolete).

                              Grid squares may be in 6-character form (as above) or in the shortened
                              4-character form (e.g. IO91).

                              I actually raised this question a while back in the aprssig and was
                              told, again IIRC, that no popular APRS clients or sites actually
                              interpret and map stations using grid squares, which is a good reason
                              for WinLink to not use these formats. We were looking for a way to
                              shorten position packets from APRS Messenger on 30m HF.

                              Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
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