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dave and jaime

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Everything posted by dave and jaime

  1. To the best of my knowledge, this Sony GPS was one of the first "consumer" handheld GPS units on the market! (circa 1990) It does not have all the bells and wistles of todays GPS units, but it is an extreemly well built unit. IMO Also, it has always amazed me what the prices are for "NEW" technology when it first hits the market place!!! Here is an article that lists the price for my dinosaur GPS. Where Am I? No matter where in the world you are, the $1,195 hand-held Sony Pyxis GPS (Global Positioning System) can identify your precise position within about 100 feet. The Pyxis communicates with four satellites to identify your longitude, latitude, and altitude. With Pyxis you may still get lost, but at least you'll know exactly where you are. (Sony: 201-930-7669) http://www.wired.com/wired/archive/1.01/fetish.html I purchased this Sony GPS'r (NIB) at a yard sale quite a few years ago! not quite, magellan introduced the first handheld gps unit in 1989 and it was the nav1000. for history, try searching wikipedia for thalles.
  2. I used a GPS300 (a very similar model), and they are not very sensitive. Mine would take up to ten minutes to get an initial fix, and woud be next to useless on really overcast days. Using really fresh alkaline batteries seemed to help a bit. the gps 300 wasnt a close relative of the 315/320/330 family. the gps 310 was a relative of the 315 etc, the gps 300 wasnt a 12 channel parallel unit and was far below the 12 chan units such as the 315/320/330. as for the orginal posters 315, it could be a couple of things. assuming you have given it enough time to initialize(~10-15 minutes), it might be worth your while to do a system check by pressing: MENU; <RIGHT>; <LEFT>; <RIGHT>. there are options here to check the flash, display etc. failing that, it is also possible that the backup battery has failed and that has caused some units to cease functioning. you can access some of the undocumented tech stuff at gpsinformation.net.
  3. since you list cad as an occupation the easiest way is to use grid coordinates(utm, mtm etc) from the gps to create a pline in autocad and then select the properties and area bounded by the line is listed.
  4. checking out your page (http://www.mtgc.org/robertlipe/myfaq/Magellan_FAQ.shtml), you have the following section: "Cables/Cabling Are the serial/power cables for all units mechanically identical? Almost. The head on the cables for the SporTrak and Meridian families are identical. The housing of the 330 (and 315 and predecessors not covered by this FAQ) has a flat back while the newer models have a curve to them. The pinouts are the same and it's possible, if you're patient enough, to use the cable from one family on the other if you bend the "fingers" on the cable out to increase their reach a little." are you sure of the models with the curved and flat rear housing? i think you have it reversed.
  5. http://www.lyngsat.com/tracker/g15.html According to that site, the Galaxy 15 (Garmin 48) is below the horizon, right below the equator. It really doesn't appear you are helping much if any in this discussion, and just hear to bash Garmin handhelds. This was about someone asking if differential data is even needed for caching, which it clearly is not. i think the reference to garmins handling of waas is reasonable, at least in my non-waas area. the little 'd's' reference only the fact that the garmin unit is picking up signals from the waas sats, it doesnt consider whether there is an active base station in the area providing valid corrections and thus whether it should apply the corrections. in short waas is greatly overblown and to my mind provides little advantage for geocaching. the handheld units in use here are little more than toys. they have no way of knowing what their accuracy is at any given time, no way of assessing system health, and due to various manufacturer algorithms different units may give different results when side-by-side at the same time.
  6. check out the 'device manager/hardware' setting under control panel. under 'ports(com & lpt)' there should be a listing for the serial port generator, if windows recognizes it. if not, there may be a windows issue to be resolved. to me having usb connectivity wouldnt be sufficient reason to upgrade a gps.
  7. yes. infact some surveying equipment also only have a 6 digit northing and the seventh digit has to be added by the postprocessing software,(user has to have knowledge of thezone setup though).
  8. i guess theres nothing like a good old rs232 serial connection and its screws/bolts.
  9. Looks like next year as per the SatNav News is the goose bay station actually installed and tested for operation. my info from a contractor working on the job was the installation was incomplete and as a result the station was inoperable, the job was to be completed this summer. the gander station was installed and then operated for a couple of weeks last fall for commissioning.
  10. I don't know of a status page but SatNav News has articles about the new stations (link) what im looking for is an update on the new station installed in gander, and when waas will be 'acive' within my area.
  11. sorta related, where can you find the current operating status of the waas ground reference stations?
  12. not directly employed in gis, im an engineer that started as a young lad pulling the chains for surveyors etc. and graduated to being an instrument man. now my time is spent doing geology prospecting as a hobby and geotechncial research as i work in a large(5.5m boom arm centrifuge,one of the top facilities in the world) and the like. as for gis platforms, mapinfo gets very high reviews from the people here. is you need a cad/gis interface mscad works well.
  13. I am under the impression that the spheres (3 satellites and 1 earth) do not meet at one point because of factors like atmospheric distubances, signal reflection from buildings/trees/rocks/etc, the internal clock of the GPSr not being exact to the nanosecond, incorrect almanacs, etc. If I am not mistaken, the calculations are not the problem but just the factors that influence it. If we got rid of all the things throwing the calculations off, it could tell us our exact place on earth. Probably there is some function in the GPSr with plus or minuses thrown everywhere to account for the errors it finds. Standing in an open field and a link to all the satelites and WAAS available, I wouldn't be suprised if I saw 1m accuracy. But I can only dream... best I seen is 6 feet due to the precision (at best using utm its 1m in either direction, waas or not) gps cannot provide a fix better than about 2m. the errors you mention arent accounted(save for some atmospherice disturbances), even with waas corrections, for in calculation and further degrade accuracy. i would view any greater accuracy estimate as rubbish. as for the calculations, id think that due to the complexity of code used in our gps(being somewhat simplified) that this number would be slightly greater(~3-4m) as a best case accuracy when compared to survey data. this accuracy would also be further degraded when the calculations for datums are introduced. can anyone prove this wrong with other than ancedotal evidence?
  14. Hmmm... So that surveyor I was talking to, who told me he was out over the weekend and getting 3 centimeter error, is full of it? The difference is, he was using a PROFESSIONAL TOOL (receiver), and not a CONSUMER TOY (receiver). They both use the same satellites. the original post wasnt totally incorrect. professional gear such as trimble, sokkia etc uses more than just the sat signals we use in our handheld for position fixes of acceptable accuracy/precision. the professional tool, im unsure of model you reference, is more than just a reciever--it also transmits from base station to roamers for corrections, alternatively the corrections can legimately be applied after the fact provided only one instrument setup is used. while i havent used every piece of gear, i do believe there are units using the p codes previously only used by the amercian(correction anyone?) military. as for the epe reding, it is a pretty useless number, it is only an estimate of how much error the gps thinks it picked up during its calculations and modeling of datums, and does not reflect conditions, sat errors etc.
  15. that is about right for the northing difference in nad27-nad83 in newfoundland(48n 52w). the difference in the easting is only about 10-20 meters and you may not notice it on your gps unless you check against known coordinates.
  16. peter: i think we ust have crossed wires somehow. i knew that i could send my position on one rhino to another unit, but is their a way for the units to do this automatically and record the data in any meaningful fashion? are there any other recreation units that can automatically track each other? in rereading your previous post, it gives me the impression that you mean that part of the issue was that different sats would in fact make the positioning fix less accurate. in leading a engineering geomatics course, there is an exercise given to the students to introduce them to the idea of dgps. while not scientific the results i found to be interesting. the exercise is setup such that each groups has 2 identical non-waas units. one unit is placed over a horizontal control point and the roamer then cycles several points over a closed survey loop. this is repeated for several averaging times ranging from 1 min to 10 min at each station. generally, the results showed that using a simple shift equal to the error at the base station recording brought the roamer into better alignment with the station. this is an excerise in exploiting the consistancy of the system, and the most important variable appeared to be the averaging time at each station---averaging beyond 5minutes seemed to offer little benefit but averaging of less than a minute provided no worthwhile correlation. the results seemed to suggest a reliable 3-4 meter range of accuracy. ive run this exercise for several years and the results seem to be fairly consistant and at least as reliable as the gps itself.
  17. The technique you're describing is sometimes called "poor man's DGPS" and generally doesn't work well at all. The problem is that even with two receivers in reasonable proximity there's still no assurance that they'll be using the same set of satellites in performing their position calculation. If different satellites are being seen by the roaming unit then its errors may not be at all correlated with those of the fixed unit. I.e. one may be showing a position too far to the west while the other is off to the east and applying the 'correction' in that case will only make the position worse. Various averaging and similar techniques used by the Kalman filter algorithms in the receivers further uncorrelate their errors. Use of WAAS would be far superior and also more convenient in areas where it's available. True DGPS determines corrections for each satellite separately so the roaming receiver can apply them properly to the satellites it is seeing at the time. When post-processing is used the roaming receiver records information separately for each satellite so the per-satellite corrections can be properly applied and corrected positions determined. One application for sending the NMEA stream from one GPS receiver to another is to have the second receiver display the position of the first on its screen. Of course you need a communication link between the two to make this useful. It's sometimes used in combination with APRS Ham radio networks to display the positions of multiple GPS receivers. I don't know if the Legend model in particular supports that application. (The Garmin Rino models use the FRS/GMRS radio channels to send this information and display the positions of other compatible models.) granted, the sat group used for calculations may not be the same but the if using 'similar' gps units the errors introduced by the algorithims would infact be nearly eliminated, not magnified. also by using a time sync, enviromental errors, save for multipath, would largely be eliminated. that leaves errors introduced by using different sats, since the gps system is only generally accurate, in practice use confirms that you dont get any better accuracy using sats 8, 11, 15, 24, 25 as opposed to 13, 17, 6, 28, 30. one thing i never mentioned in my original post is that allowing sufficient averaging time for the gps to gain an accurate fix is critical--whether the unit is a consumer or professional unit. i guess my point is that this system, as used here, was never meant to give meter accuracy and further to that, in situ experience shows that the system is reasonably consistant and using this type of procedure doesnt markedly degrade accuracy. sorry for being ignorant/uniformed, but do the rhinos send their positional data over the gmrs/frs bands to other rhino units?
  18. In Appendix F it talks about the wiring diagram and it says this: Interface formats are selected from teh Setup 'Interface Page' on page 46 of this manual. The input/output lines on your eTrex Legend unit are RS-232 compatible, allowing easy interface to a wide range of external devices, including PC's, differential beacons receivers, marine autopilots and/or a second GPS receiver. The NMEA 0183 version 3.0 interface format is supported by the eTrex Legend and enables the unit to drive up to three NMEA devices. Ok, so how does one go about hooking up two GPS'? And again what would be the benifit of doing so? i think that maybe connecting to a second gps would be similar to connecting 2 graphic calculators together to transfer data from one to the other. i dont think that 2 gps can be connected directly to give improved accuracy.
  19. while you wont be able to get 'survey' type accuracy, it is common practice to place one unit over a known point and do the roaming with another reciever. the base station display would be recorded at the same time as the roamer and corrections(the corrections being the difference between the base station and the known coordinate) would be applied after the fact to the roamer recordings, this would be the post-processing mentioned earlier. obviously this wont give you accuracy as obtained by commercial gear, as precision of recreational units is limited to 1 meter at best, but is frequently done in many geomatics/cartographic university programs to introduce students to the process. if you are using similar(read same manufacturer) units for the base and roamer you can be reasonably assured that the corrections are valid and would probably provide a better set of coordinates than can be achieved by current waas corrections. using a process like this would be essentially 'tying to a control'. if accuracy is your goal, it would also be worthwhile to checkout one of the mission planning software packages, leica makes a very good one.
  20. this isnt a new phenomna(sp??), but the chemicial(s) generally blamed are the hydrocarbons. some news hogs around may recall incidents of 'gas' sniffing in some northern canadian cities and the public outcry from about 5-10 years ago. this is also similar to the starting fluid used for diesel engines and most heavy mechanics can attest to the buzz if using the stuff in confined spaces.
  21. not really. however most gps manufacturers refer to pois as waypoints that cannot be erased from the gps. so, essentially waypoints are user entered/erasable pois and pois are permanant waypoints entered into the firmware by the manufacturer. having said that it is possible with some advanced skills, or software, to replace the hard coded pois with user points. it is also often possible to replace the pois of an 'landbased' gps with the 'marine' poi database for the same unit.
  22. safety is a definate issue for a pace car. if safety for brake pull is your concern, maybe you misunderstood my thought...i was thinking more along the lines of a lead pace car as in a horse/car race, safety is definately a concern regardless.
  23. the best thing about the onstar in my 3/4 ton gmc truck is that it can be 'hacked' to output a nema stream to my laptop for the gis software to do the real navigating. problem with these type of products is that you typically have either hybrid products(which rarely do both thing exceptionally) and or companies that are out of their typicial product base(pioneer make decent stereo gear, gps i kinda wonder).
  24. i have 2 initial suggestions, neither of which involve gps that may interest you. 1)you could use a pace car if there are no safety concerns, space becomes an issue. for our event we were using an abandoned amercian air force base and the space/safety issue wasnt a concern except that we were traveling at 250 km/hr. 2)local law enforcement. here, for similar type of events, weve been able to get local law enforcement to 'donate' their radar guns for use by a retired member of the force. by 'donate', it did tale a donation to a local charity for them to agree, they also provide some very good safety seminars for the contestants and they also got the opportunity for an off duty officer to liason with public in a fun event. my suggestion for a gps unit wuld be nearly any basic unit. my experience with gps primarily involves magellan/thalles unit (though a new member is the garmin 276c). the magellan units as notes contain a large display screen feature with 3/4" high digits specifically designed for use while driving. otherwise my reccomendation would be to research your purchase and buy what unit you feel youd like---im sure youll find other uses for it. i dont really think it would be necessary to have identical units as the data being feed into the units is the same and the computation process varies very little between manufacturers. gps may pose some troulbes as some vehiciles have metallic laminated glass which may impair signal reception.
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