Is one GPS receiver enough to get the precise position? Or we need to use multiple GPS receivers, for instance, four GPS receivers installed on bow, tail, port and starboard, respectively? If we use four GPS receivers, how to manipulate the GPS information collected by these four receivers to get the precise position of the ship?
GPS Navigation for Ship - Single Receiver or Multiple Receivers?
Started by ●June 9, 2004
Reply by ●June 9, 20042004-06-09
The system you are describing is a GPS based attitude indication system to replace (augment?) gyros in a ship that is used as a sonar platform to correct for ship attitude in the data. I'm not sure how many companies are making such systems now, but a flip through any Oceanographic oriented (oil industry) magazine will yield vendors. Adding GPS recievers will not yield (much) better position accuracy, but if used as in the systems above will yield accurate and timely attitude measurements. Al... "Yan.L" <waters@starhub.net.sg> wrote in message news:df850db4.0406090812.4e8f7865@posting.google.com...> Is one GPS receiver enough to get the precise position? Or we need to > use multiple GPS receivers, for instance, four GPS receivers installed > on bow, tail, port and starboard, respectively? > > If we use four GPS receivers, how to manipulate the GPS information > collected by these four receivers to get the precise position of the > ship?
Reply by ●June 9, 20042004-06-09
Yan.L wrote:> Is one GPS receiver enough to get the precise position? Or we need to > use multiple GPS receivers, for instance, four GPS receivers installed > on bow, tail, port and starboard, respectively? > > If we use four GPS receivers, how to manipulate the GPS information > collected by these four receivers to get the precise position of the > ship?A GPS on the bridge will give you the location of the bridge. One each on bow and stern will provide enough information to correct the compass. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 9, 20042004-06-09
"Yan.L" schrieb:> If we use four GPS receivers, how to manipulate the GPS information > collected by these four receivers to get the precise position of the > ship?Two receivers would usually be sufficient, on bow and tail (however, most people get away with one - because using a compass will give you the necessary information). You can setup such a system yourself - there are products on the market which do the integration of the two signals. It would probably be not too complicated to add dual receiver support to a Windows application. But I guess most people can get away with a GPS with integrated compass. - Carsten -- Audio Visual Systems fon: +49 (0)2234 601886 Carsten Kurz fax: +49 (0)2234 601887 Von-Werth-Stra�e 111 email: audiovisual@t-online.de 50259 Pulheim / Germany WGS84:N50�57'50.2" E06�47'28.5"
Reply by ●June 9, 20042004-06-09
In order to improve on the raw GPS accuracy, you have two options I am aware of, neither of which fits the bill in this case. The first is time averaging over an extended interval, which is used for surveying. This obviously is not compatible with a moving vehicle or ship. The second involves placing a second GPS at a known fixed location somewhat near the area of the GPS on the moving platform and using the errors in its readings to correct the moving GPS position. This is differential GPS, which is usable for things like precision approaches to airports (there are two versions of that, a wide area version covers a larger area but at reduced precision, a local area one that needs the second receiver fairly close by but is only effective for a relatively small local area). You could use other sensors (inertial or Loran) combined with the GPS current position and recent history to get some of the advantages of the time averaging at the expense of more processing. "Yan.L" wrote:> Is one GPS receiver enough to get the precise position? Or we need to > use multiple GPS receivers, for instance, four GPS receivers installed > on bow, tail, port and starboard, respectively? > > If we use four GPS receivers, how to manipulate the GPS information > collected by these four receivers to get the precise position of the > ship?-- --Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 email ray@andraka.com http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759
Reply by ●June 9, 20042004-06-09
I have two bottom-of-the-line eTrex's on my bicycle (result of an unexpectedly permanent temporary repair of one with electrical tape and balled-up packing peanut); they read very close but not always in the last digit; and altitudes typically differ by ten feet. Obviously averaging would do something here. On the other hand, on a bicycle the signal received is not always good, and the GPS's differ in what satellites my body blocks. Actual usefulness is displaying different scales of the breadcrumb dropping maps at the same time. -- Ron Hardin rhhardin@mindspring.com On the internet, nobody knows you're a jerk.
Reply by ●June 9, 20042004-06-09
Ron Hardin schrieb:> > I have two bottom-of-the-line eTrex's on my bicycle (result of an > unexpectedly permanent temporary repair of one with electrical tape > and balled-up packing peanut); they read very close but not always in > the last digit; and altitudes typically differ by ten feet. Obviously > averaging would do something here. On the other hand, on a bicycle > the signal received is not always good, and the GPS's differ in what > satellites my body blocks.What the OP paster was after is a GPS based attitude indicator. Ships and planes have the ability to drift to a different direction than they are heading. A GPS will only show the travel direction of the receiver, not the heading of the vehicle. If you have two receivers on opposite ends of the vehicle (or simply spaced apart as much as possible), their positions can be calculated into the heading of the vehicle across the axis between both receivers. A compass, of course, can do the same, but compasses need to be adjusted to the magnetic declination for specific areas of the world, and such a GPS based attitude measurement can aid in making the heading data more precise. - Carsten -- Audio Visual Systems fon: +49 (0)2234 601886 Carsten Kurz fax: +49 (0)2234 601887 Von-Werth-Stra�e 111 email: audiovisual@t-online.de 50259 Pulheim / Germany WGS84:N50�57'50.2" E06�47'28.5"
Reply by ●June 9, 20042004-06-09
Hello Ray and others, The U.S. Coast Guard is currently working on a Nationwide Differential GPS network. Some info here: http://www.tfhrc.gov/its/ndgps/02072.htm http://www.navcen.uscg.gov/dgps/ndgps/default.htm http://www.uscg.mil/hq/g-cp/comrel/factfile/Factcards/DGPS.html I hope this helps, Clay "Ray Andraka" <ray@andraka.com> wrote in message news:40C74F5F.378AA0EB@andraka.com...> In order to improve on the raw GPS accuracy, you have two options I am > aware of, neither of which fits the bill in this case. The first is time > averaging over an extended interval, which is used for surveying. This > obviously is not compatible with a moving vehicle or ship. The second > involves placing a second GPS at a known fixed location somewhat near the > area of the GPS on the moving platform and using the errors in its > readings to correct the moving GPS position. This is differential GPS, > which is usable for things like precision approaches to airports (there > are two versions of that, a wide area version covers a larger area but at > reduced precision, a local area one that needs the second receiver fairly > close by but is only effective for a relatively small local area). You > could use other sensors (inertial or Loran) combined with the GPS current > position and recent history to get some of the advantages of the time > averaging at the expense of more processing. > > "Yan.L" wrote: > > > Is one GPS receiver enough to get the precise position? Or we need to > > use multiple GPS receivers, for instance, four GPS receivers installed > > on bow, tail, port and starboard, respectively? > > > > If we use four GPS receivers, how to manipulate the GPS information > > collected by these four receivers to get the precise position of the > > ship? > > -- > --Ray Andraka, P.E. > President, the Andraka Consulting Group, Inc. > 401/884-7930 Fax 401/884-7950 > email ray@andraka.com > http://www.andraka.com > > "They that give up essential liberty to obtain a little > temporary safety deserve neither liberty nor safety." > -Benjamin Franklin, 1759 > >
Reply by ●June 9, 20042004-06-09
Ray Andraka wrote:> In order to improve on the raw GPS accuracy, you have two options I am > aware of, neither of which fits the bill in this case. The first is time > averaging over an extended interval, which is used for surveying. This > obviously is not compatible with a moving vehicle or ship. The second > involves placing a second GPS at a known fixed location somewhat near the > area of the GPS on the moving platform and using the errors in its > readings to correct the moving GPS position. This is differential GPS, > which is usable for things like precision approaches to airports (there > are two versions of that, a wide area version covers a larger area but at > reduced precision, a local area one that needs the second receiver fairly > close by but is only effective for a relatively small local area). You > could use other sensors (inertial or Loran) combined with the GPS current > position and recent history to get some of the advantages of the time > averaging at the expense of more processing.Because the bow and stern receivers are subject to the same positional errors, heading accuracy is not improved even with a short-range differential system. Heading accuracy depends on differences of large numbers, but the errors of both numbers are highly correlated. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 9, 20042004-06-09
Clay Turner wrote:> Hello Ray and others, > > The U.S. Coast Guard is currently working on a Nationwide Differential GPS > network. > > Some info here: > > http://www.tfhrc.gov/its/ndgps/02072.htm > > http://www.navcen.uscg.gov/dgps/ndgps/default.htm > > http://www.uscg.mil/hq/g-cp/comrel/factfile/Factcards/DGPS.html > > > I hope this helps, > > Clay > > > "Ray Andraka" <ray@andraka.com> wrote in message > news:40C74F5F.378AA0EB@andraka.com... > >>In order to improve on the raw GPS accuracy, you have two options I am >>aware of, neither of which fits the bill in this case. The first is time >>averaging over an extended interval, which is used for surveying. This >>obviously is not compatible with a moving vehicle or ship. The second >>involves placing a second GPS at a known fixed location somewhat near the >>area of the GPS on the moving platform and using the errors in its >>readings to correct the moving GPS position. This is differential GPS, >>which is usable for things like precision approaches to airports (there >>are two versions of that, a wide area version covers a larger area but at >>reduced precision, a local area one that needs the second receiver fairly >>close by but is only effective for a relatively small local area). You >>could use other sensors (inertial or Loran) combined with the GPS current >>position and recent history to get some of the advantages of the time >>averaging at the expense of more processing. >> >>"Yan.L" wrote: >> >> >>>Is one GPS receiver enough to get the precise position? Or we need to >>>use multiple GPS receivers, for instance, four GPS receivers installed >>>on bow, tail, port and starboard, respectively? >>> >>>If we use four GPS receivers, how to manipulate the GPS information >>>collected by these four receivers to get the precise position of the >>>ship? >> >>-- >>--Ray Andraka, P.E. >>President, the Andraka Consulting Group, Inc. >>401/884-7930 Fax 401/884-7950 >>email ray@andraka.com >>http://www.andraka.com >> >> "They that give up essential liberty to obtain a little >> temporary safety deserve neither liberty nor safety." >> -Benjamin Franklin, 1759 >> >> > > >The USCG DGPS service has been operational around the coasts of the US for about 5 years now. In 1989 I designed and built what my thesis adviser claimed was the 3rd datalink receiver for that service. It was used for several years in investigating various FEC algorithms etc., so the USCG could decide on the best modulation strategy. According to their website the USCG DGPS service will locate you to a 2 meter circle (with selective availability turned off). I have no idea if other countries support DGPS, but there's no reason they couldn't. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
