Re: [Xastir] Question about APRS GPS position precision
Which tells us nothing. You don't tell me the origins of your map sources, the datum, the satellite constellation, antenna occlusions, etc. All these affect how good your accuracy is for GPS positioning. Or, was this simply flame-bait? gerry Andrew Rich wrote: Yeah but in the real world, it still puts me off the road or runway. Andrew Rich VK4TEC [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> http://www.tech-software.net -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Gerry Creager Sent: Monday, 8 October 2007 6:54 AM To: Richard Polivka, N6NKO Cc: Jim Tolbert; XASTIR Subject: Re: [Xastir] Question about APRS GPS position precision Richard Polivka, N6NKO wrote: Jim, Most GPS units are good to 4 decimals. Any higher precision requires post-processing or L1/L2 reception (not avail in consumer equipment). When you factor in multipath and all the other variables, 4 decimals is quite good but it takes time and patience - think searching for a geocache in a forest. Plus, at four decimals, on a patch antenna minus ground plane, it is quite unstable. 9 cm more or less should be plenty good enough for most of our users. That's 4 decimal-place precision. That said, an L1 signal (L5 won't be available for some time still) position assuming really good geometry and a stable antenna platform is likely to be good only to ~6m horizontal and ~13.7m vertical... at best. Plus, I have a feeling that when Bob B. designed APRS, he was not looking at this being used for what we are doing. Until the data output is smoother and better accuracy, five decimals in - broadcast 4 - rewrite the standard, this may be the best for now. The limitations in precision are in rank order, the spec and the spec. For accuracy the limitations are: User equipment antenna configuration Ionosphere Troposphere Multipath GPS Signal Specification for L1 When I resolve cm accuracy, or better, I do it using dual-frequency (L1/L2) receivers, multiple stable baseline processing on ground-plane or choke-ring antennas, at a fixed and measured height about the ground, and post-process the data to include a least-squares adjustment of the position. The process is as much statistical as matrix-mathematical in accomplishment. gerry Jim Tolbert wrote: Hi, all.. I have been told that the limiting factor in position precision is the APRS system transmission standard-- that transmissions are limited to 1/1000th of a degree or approximately +/- 60 feet. Is this true? If so, why? If not, what is the limiting element in the final display of tracker position on Xastir? For those of you using Xastir for Search & Rescue, do you run on the APRS frequency or a different (quiet) frequency? What are the arguments for each school of thought? We are going to be running some field tests in the near future with a variety of equipment setups does anyone have suggestions of things we should test? We have a list, but new ideas and comments would be appreciated from those that have already taken the stumbles. Many thanx.. jt ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir -- Gerry Creager -- [EMAIL PROTECTED] Texas Mesonet -- AATLT, Texas A&M University Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983 Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843 ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir -- Gerry Creager -- [EMAIL PROTECTED] Texas Mesonet -- AATLT, Texas A&M University Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983 Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843 ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Question about APRS GPS position precision
Andrew Rich wrote: Yeah but in the real world, it still puts me off the road or runway. Andrew Rich VK4TEC [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> http://www.tech-software.net -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Gerry Creager Sent: Monday, 8 October 2007 6:54 AM To: Richard Polivka, N6NKO Cc: Jim Tolbert; XASTIR Subject: Re: [Xastir] Question about APRS GPS position precision Richard Polivka, N6NKO wrote: Jim, Most GPS units are good to 4 decimals. Any higher precision requires post-processing or L1/L2 reception (not avail in consumer equipment). When you factor in multipath and all the other variables, 4 decimals is quite good but it takes time and patience - think searching for a geocache in a forest. Plus, at four decimals, on a patch antenna minus ground plane, it is quite unstable. 9 cm more or less should be plenty good enough for most of our users. That's 4 decimal-place precision. That said, an L1 signal (L5 won't be available for some time still) position assuming really good geometry and a stable antenna platform is likely to be good only to ~6m horizontal and ~13.7m vertical... at best. Plus, I have a feeling that when Bob B. designed APRS, he was not looking at this being used for what we are doing. Until the data output is smoother and better accuracy, five decimals in - broadcast 4 - rewrite the standard, this may be the best for now. The limitations in precision are in rank order, the spec and the spec. For accuracy the limitations are: User equipment antenna configuration Ionosphere Troposphere Multipath GPS Signal Specification for L1 When I resolve cm accuracy, or better, I do it using dual-frequency (L1/L2) receivers, multiple stable baseline processing on ground-plane or choke-ring antennas, at a fixed and measured height about the ground, and post-process the data to include a least-squares adjustment of the position. The process is as much statistical as matrix-mathematical in accomplishment. gerry Well, worst case is I am still within shouting distance. Not bad by any means. Steve/WM5Z ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Question about APRS GPS position precision
On Sun, Oct 07, 2007 at 10:09:42AM -0700, we recorded a bogon-computron collision of the <[EMAIL PROTECTED]> flavor, containing: > > Bob Bruninga came up with yet another method of adding precision, > called DAO. With this method you add some extra characters to the > comment field that give you the extra precision _and_ specify the > datum for the posit. Very few APRS clients have implemented DAO at > this time. Bob likes it because it doesn't make the Kenwood radios > obsolete I think. As I recall the Kenwoods can handle Base-91 just > fine for posits, but have a problem with Base-91 "Objects" or maybe > it was just Base-91 "Items". The kenwood D7&D700 don't understand Items at all, and can't deal with base-91 objects. They handle base-91 posits Just Fine. I don't quite understand why they'd do that in the firmware --- if they're going to bother writing code to handle base-91, why not let it apply to all types of position reports? But there you have it. I don't know if the D710 supports base-91 fully. Since Bob is so down on base-91 now and he had Kenwood's ear, I suppose not. The big advantage of DAO is that stations that don't understand it just ignore the extra digits of precision it offers, and treat the packet as a regular un-compressed posit. There are numerous statements flying around in APRSSIG that Xastir supports DAO, but as far as I can tell this is incorrect, and Xastir knows nothing about DAO. -- Tom RussoKM5VY SAR502 DM64ux http://www.swcp.com/~russo/ Tijeras, NM QRPL#1592 K2#398 SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM "And, isn't sanity really just a one-trick pony anyway? I mean all you get is one trick, rational thinking, but when you're good and crazy, oooh, oooh, oooh, the sky is the limit!" --- The Tick ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
RE: [Xastir] Question about APRS GPS position precision
Yeah but in the real world, it still puts me off the road or runway. Andrew Rich VK4TEC [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> http://www.tech-software.net -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Gerry Creager Sent: Monday, 8 October 2007 6:54 AM To: Richard Polivka, N6NKO Cc: Jim Tolbert; XASTIR Subject: Re: [Xastir] Question about APRS GPS position precision Richard Polivka, N6NKO wrote: > Jim, > > Most GPS units are good to 4 decimals. Any higher precision requires > post-processing or L1/L2 reception (not avail in consumer equipment). > When you factor in multipath and all the other variables, 4 decimals is > quite good but it takes time and patience - think searching for a > geocache in a forest. Plus, at four decimals, on a patch antenna minus > ground plane, it is quite unstable. 9 cm more or less should be plenty good enough for most of our users. That's 4 decimal-place precision. That said, an L1 signal (L5 won't be available for some time still) position assuming really good geometry and a stable antenna platform is likely to be good only to ~6m horizontal and ~13.7m vertical... at best. > Plus, I have a feeling that when Bob B. designed APRS, he was not > looking at this being used for what we are doing. > > Until the data output is smoother and better accuracy, five decimals in > - broadcast 4 - rewrite the standard, this may be the best for now. The limitations in precision are in rank order, the spec and the spec. For accuracy the limitations are: User equipment antenna configuration Ionosphere Troposphere Multipath GPS Signal Specification for L1 When I resolve cm accuracy, or better, I do it using dual-frequency (L1/L2) receivers, multiple stable baseline processing on ground-plane or choke-ring antennas, at a fixed and measured height about the ground, and post-process the data to include a least-squares adjustment of the position. The process is as much statistical as matrix-mathematical in accomplishment. gerry > Jim Tolbert wrote: >> Hi, all.. >> >> I have been told that the limiting factor in position precision is the >> APRS system transmission standard-- that transmissions are limited to >> 1/1000th of a degree or approximately +/- 60 feet. Is this true? If >> so, why? >> >> If not, what is the limiting element in the final display of tracker >> position on Xastir? >> >> For those of you using Xastir for Search & Rescue, do you run on the >> APRS frequency or a different (quiet) frequency? What are the >> arguments for each school of thought? We are going to be running >> some field tests in the near future with a variety of equipment >> setups does anyone have suggestions of things we should test? We >> have a list, but new ideas and comments would be appreciated from >> those that have already taken the stumbles. >> >> Many thanx.. jt >> > ___ > Xastir mailing list > Xastir@xastir.org > http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir -- Gerry Creager -- [EMAIL PROTECTED] Texas Mesonet -- AATLT, Texas A&M University Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983 Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843 ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Question about APRS GPS position precision
Richard Polivka, N6NKO wrote: Jim, Most GPS units are good to 4 decimals. Any higher precision requires post-processing or L1/L2 reception (not avail in consumer equipment). When you factor in multipath and all the other variables, 4 decimals is quite good but it takes time and patience - think searching for a geocache in a forest. Plus, at four decimals, on a patch antenna minus ground plane, it is quite unstable. 9 cm more or less should be plenty good enough for most of our users. That's 4 decimal-place precision. That said, an L1 signal (L5 won't be available for some time still) position assuming really good geometry and a stable antenna platform is likely to be good only to ~6m horizontal and ~13.7m vertical... at best. Plus, I have a feeling that when Bob B. designed APRS, he was not looking at this being used for what we are doing. Until the data output is smoother and better accuracy, five decimals in - broadcast 4 - rewrite the standard, this may be the best for now. The limitations in precision are in rank order, the spec and the spec. For accuracy the limitations are: User equipment antenna configuration Ionosphere Troposphere Multipath GPS Signal Specification for L1 When I resolve cm accuracy, or better, I do it using dual-frequency (L1/L2) receivers, multiple stable baseline processing on ground-plane or choke-ring antennas, at a fixed and measured height about the ground, and post-process the data to include a least-squares adjustment of the position. The process is as much statistical as matrix-mathematical in accomplishment. gerry Jim Tolbert wrote: Hi, all.. I have been told that the limiting factor in position precision is the APRS system transmission standard-- that transmissions are limited to 1/1000th of a degree or approximately +/- 60 feet. Is this true? If so, why? If not, what is the limiting element in the final display of tracker position on Xastir? For those of you using Xastir for Search & Rescue, do you run on the APRS frequency or a different (quiet) frequency? What are the arguments for each school of thought? We are going to be running some field tests in the near future with a variety of equipment setups does anyone have suggestions of things we should test? We have a list, but new ideas and comments would be appreciated from those that have already taken the stumbles. Many thanx.. jt ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir -- Gerry Creager -- [EMAIL PROTECTED] Texas Mesonet -- AATLT, Texas A&M University Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983 Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843 ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Question about APRS GPS position precision
On Sun, 7 Oct 2007, Jim Tolbert wrote: > I have been told that the limiting factor in position precision is the > APRS system transmission standard-- that transmissions are limited to > 1/1000th of a degree or approximately +/- 60 feet. Is this true? If > so, why? Mic-E format or "standard" APRS format, yes. In my neck of the woods it describes a box of about 60' by 40'. Xastir users can zoom way in on a station and (perhaps) see a white box. That describes the precision they are transmitting. Stations that are transmitting NMEA sentences directly that have 3 or 4 digits after the decimal will display a smaller box. So will stations that are transmitting Base-91 packets, which Xastir and OpenTrackers are capable of sending. For Base-91 it's something like a 2' by 3' box (in my area). Look at any D700/D710/D7A station to see the larger box. The box in Xastir shows where they _might_ be based on what they are transmitting, and the box is oriented in the correct direction for the truncated digits in each hemisphere. Bob Bruninga came up with yet another method of adding precision, called DAO. With this method you add some extra characters to the comment field that give you the extra precision _and_ specify the datum for the posit. Very few APRS clients have implemented DAO at this time. Bob likes it because it doesn't make the Kenwood radios obsolete I think. As I recall the Kenwoods can handle Base-91 just fine for posits, but have a problem with Base-91 "Objects" or maybe it was just Base-91 "Items". > If not, what is the limiting element in the final display of tracker > position on Xastir? *) Accuracy of the GPS position of the tracker. *) Precision transmitted across the air. *) Accuracy of your base maps. *) Registration of your base maps. *) Datum of your maps vs. what you mapping software can do. *) Projection of your maps vs. what your mapping software can do. *) Accuracy of your mapping software in displaying those maps. > For those of you using Xastir for Search & Rescue, do you run on the > APRS frequency or a different (quiet) frequency? What are the > arguments for each school of thought? We are going to be running some > field tests in the near future with a variety of equipment setups > does anyone have suggestions of things we should test? We have a list, > but new ideas and comments would be appreciated from those that have > already taken the stumbles. I have a lot to say on this subject but have said much of it before on the SAR_APRS list. Perhaps read up on it there and then discuss more about it there? -- Curt, WE7U: XASTIR: "Lotto: A tax on people who are bad at math." -- unknown "Windows: Microsoft's tax on computer illiterates." -- WE7U The world DOES revolve around me: I picked the coordinate system! ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Question about APRS GPS position precision
Jim, Most GPS units are good to 4 decimals. Any higher precision requires post-processing or L1/L2 reception (not avail in consumer equipment). When you factor in multipath and all the other variables, 4 decimals is quite good but it takes time and patience - think searching for a geocache in a forest. Plus, at four decimals, on a patch antenna minus ground plane, it is quite unstable. Plus, I have a feeling that when Bob B. designed APRS, he was not looking at this being used for what we are doing. Until the data output is smoother and better accuracy, five decimals in - broadcast 4 - rewrite the standard, this may be the best for now. 73 from 807, Richard, N6NKO Jim Tolbert wrote: Hi, all.. I have been told that the limiting factor in position precision is the APRS system transmission standard-- that transmissions are limited to 1/1000th of a degree or approximately +/- 60 feet. Is this true? If so, why? If not, what is the limiting element in the final display of tracker position on Xastir? For those of you using Xastir for Search & Rescue, do you run on the APRS frequency or a different (quiet) frequency? What are the arguments for each school of thought? We are going to be running some field tests in the near future with a variety of equipment setups does anyone have suggestions of things we should test? We have a list, but new ideas and comments would be appreciated from those that have already taken the stumbles. Many thanx.. jt ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
[Xastir] Question about APRS GPS position precision
Hi, all.. I have been told that the limiting factor in position precision is the APRS system transmission standard-- that transmissions are limited to 1/1000th of a degree or approximately +/- 60 feet. Is this true? If so, why? If not, what is the limiting element in the final display of tracker position on Xastir? For those of you using Xastir for Search & Rescue, do you run on the APRS frequency or a different (quiet) frequency? What are the arguments for each school of thought? We are going to be running some field tests in the near future with a variety of equipment setups does anyone have suggestions of things we should test? We have a list, but new ideas and comments would be appreciated from those that have already taken the stumbles. Many thanx.. jt -- Jim Tolbert RiverRidge Consulting, LLC PO Box 536 Webster, WI 54893 715-866-4398 home office 715-349-8993 fax [EMAIL PROTECTED] ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
