GPS/Delorme street atlas 7.0

[shoveljunk]

I saw an article in TDR issue 38 about traveling with street Atlas in conjunction with a laptop. I am trying to track my currant position while traveling. For now I am able to get a 3D fix, but it is 0. 26 tenths of a mile off of my actual position. I am using a Garmin E-Trex with interface adapter. A Belkin serial adapter to USB into a IBM thinkpad with the Street Atlas USA 7. 0. Can this error be corrected? I like the laptop despite it's size. SA 7. 0 is a great tool and would like to keep it. what other software are any of you using (if any). I get the feeling this is a rare subject.

While traveling with my wife, we used the map program to calculate distance and mileage, find groceries and laundry service. It a great tool. It would be better if I could track my position. I would also feel better about my wife navigating on her own with this tool. THANK for any help!

 

[vinceharris]

GPS/ Delorme SA 7.0

I have the same program you have and I love it . for my anttina i use is Delorme's Earthmate and it is always on track. i used it this past weekend going up to Lansing, MI. had to use my old lap top to run using the serial port and mouse port. my new lap top will be using the usb port for faster run's but delorme is out of stock.

so try changing antinnas to see if it works.



Vince Harris

member GLTDR



p. s. don't use Rand Mc Nalley's GPS it crash's.

p. s. s. sorry i use Street Atlas 2003 USA with split sceen GPS tracking





99 2500 4x4 24v ISB white/driftwood

 

[TowPro]

. 26 Tenths, I assume you have the dot in the right place.

1 miles is 5500', so 1 tenth is 550 feet, so . 1 tenth is 55', so you are off around 143'



GPS should get you down closer then that, maybe 35 feet on a bad day. BUT delorme was using maps that were older then GPS, and not sure how exact they are.



Version 7 is OK, but has some problems, Version 8 they went to a different company for map data, it was real bad. I even returned it and got my money back. Road named wrong, extra roads, missing roads, etc.



I have version 9 now. For 9 I was told they went back to version 7 maps, plus added changes users reported to them. I Can't get the voice to work, but the maps seem better. I used it to go to GA (with many programed stops) at Thanksgiving with no problems.



What I want is the new version they sell now, it has this feature where you can put map overlays on it. With the overlay companies like Walmart make an overlay that show where all the walmarts are located.



Just drive around with it, see if it stay on the road most of the time (some times it gets off even major highways a good bit)



Keep in mine when using GPS, at 55mph you are moving faster then the GPS records on the map at times, its easy to miss exits!



Besides that, Delorme and GPS are the best thing that ever was made to keep me married while traveling in the RV No more "Map Fights"

Originally posted by shoveljunk

For now I am able to get a 3D fix, but it is 0. 26 tenths of a mile off of my actual position. . THANK for any help!

 

[Dennis Garrett]

Here are some good GPS info links that might be of use.



http://gpsinformation.net/

http://www.gpsinformation.org/dale/wgarmin.htm

http://www.gpsinformation.net/etrexlegend.htm

 

[Thomas]

"it is 0. 26 tenths of a mile off of my actual position"



. 26 tenths is 26/1000 of a mile, a bit over 137 feet. Is this what you mean?



I've been playing GPS for a number of years and have yet to encounter a situation where a GPS receiver gives a consistent error. What are you using as your reference to determine that you have an error? The data bases that mapping software uses to display maps can have errors in street location and the like. Can you give a better description of how your error shows itself?

 

[jponder]

I use a Garmin etrek with Map tech software. When using the 1:24000 topo maps that show section lines I am right on the money. I am looking for section lines on timberland so I dont care about up to date road inf. It works great I can calculate areas which is a big advantage. I bought the etrek Legend this year for 198 - 50 rebate for $148 cost and it has a base map and can calculate areas on its own. The only downside is the garmins go to a decimal at . 1 miles so instead of feet you get decimal miles. One side of my property is . 75 miles and you loose some accuracy with that, of course you can always correct by just using the lat/lon coordinates. GPS SURE IS FUN!

 

[Kingram]

I also use the Delorme Earthmate GPS unit with my Street Atlas, so I don't have your exact setup. But, I do agree with others, the acuracy of the base mapping combined with the error you WILL get from the GPS receiver will add up.



Back in the days of SA (selective availability, when the Gov scrambled the GPS signals), it wasn't uncommon to get +/- 100 meters. As a matter of fact, that was the advertised error with any receiver unless you used base station data and post processed (differential corrected) the data. Then you can get MM accuracy. Actually, I got much less than 100 meter errors, but that was the "advertised" rate.



Also, most of the street data that these mapping companies use is Tiger data used during census collection. So, it isn't terribly accurate.



I wonder if the GOV is messing with the GPS accuracy due to the upcoming conflicts. I'm not sure if that is something that would happen or not.



Again, my thoughts and advice ain't worth much,



Chris

 

[HC]

Check the Map Datum

The DeLorme map datum in version 7. 0 is automatically set to WGS 84. If you're getting a consistent error, the most likely reason is that your GPS is most likely set to a different map datum. The most common with Topo maps (lower 48) is the Continental US, North American Datum of 1927. In the Legend it will be abbreviated as NAD 27 CONUS. If your Garmin is similar to mine, then follow this sequence:

Main Menu

Setup

Units

Map Datum

Highlight and change to WGS 84

(If not, look up Map datums in the Owner's manual and follow the equivalent steps to change it. )



After you've done this, report back and let us know how far off you are, in which direction, etc.



Another cause of BIG errors can be if you used the GPS at high altitude (like especially in an airplane), turned it off, and then upon landing it get's a new "fix" while incorrectly believing it is still at high altitude. The cure to that one is to look at the altitude shown BEFORE it gets a fix, and change it to the approximately correct number before the unit gets a fix. By approximately correct, I mean +/- 500 feet.

 

[shoveljunk]

GPS

I am set to wgs84. The error is a constant 2 tenth of a mile to the South East. I used the draw tool to determine the distance. I have tried all settings on the e-trex. Magnetic north, Grid, etc. No changes occured. I went and bought the SA 2003. I came up with the same error exactly. SA 2003 was returned because it was vary compicated to use and the lack of point of interrest in city limits. At my location; Street atlas N 37. 38. 76749

W 120. 55. 9490

E-trex N 37. 38. 768

W 120. 55. 954

It may be the reciever. Any way. I still like map and GPS.

 

[JHerrlich]

Just as a side note, I don't think that the government would try turning SA back on because of the potential conflict. Back when the Iraq thing first happened, they turned SA off because they didn't have enough PLGRs (military GPS). Many units in the field were relying on civilian GPSs to find their way. Honestly I don't think they have any more PLGRs than they used to.



BTW, yeah, it's probably the map datum.



PS. I remember the day they turned SA off, I didn't know they did it, but I noticed the accuracy change and no drift when sitting still.

 

[HC]

When I input those coordinates into the "lat/long" calculator I found, it said they were only 0. 0050 miles apart, or about 26 feet.



If you've got the map datums set the same, then I'd almost bet this is one of those relatively rare but quite annoying cases where the map is wrong.



Streets, especially suburban developments, are sometimes not placed exactly where planners originally mapped them out, and Street Atlas sometimes gets data from inaccurate sources. I've seen specific streets be off by a quarter mile; there's one place in Tennessee where Street Altlas clearly shows the clearing through the forest where the freeway is located as a "non-green" path. The forest cover was probably based on satellite photos. Only problem is, Street Atlas shows the freeway as being 1/2 mile North of this location, while Map Quest shows the freeway as having been relocated about 1 mile South of this location. Clearly there was some planning controversy and the map-makers got maps that showed "proposed" locations; the final location agrees with the satellite photos that you can even look at yourself on MSN's TerraServer page. Bottom line: the GPS was "right", the map was "wrong".



Try going to a geographical feature, like where two creeks join together, or where a major road crosses a creek, and see if your GPS + Delorme combo isn't right on the money. You might even see it just by getting out on a different set of roads, because maybe there's one city map or county map that had messed up coordinates and was used as an input by Delorme.



Now that I've been using a GPS for several years and seen how often the maps are wrong, I've decided that I never was lost before GPS. It's just that the maps were always wrong!

 

[shoveljunk]

My misyake.

I realized that I have not given all of you enough info. O. K. lets see if we can decipher this information.



Co-ordinance at McDonald's (Hatch & Mitchell Rd, Ceres Ca. ).

ETREX N 37. 36. 517

W 120. 56. 303

Delorme co-ordinance (using crosshair). at McDonalds

N 37. 36. 653

W 120. 56. 486



Delorme location of plot (green) tracking arrow is showing my location as Charlottesville Ln. 2 tenths of a mile South East of McDonalds. Delorme says (using crosshair).



N 37. 36. 514

W 120. 56. 3030 Same as ETREX location shown above.



I drove over to Charlottesville and the ETREX put me at,



N 37. 36. 435

W 120. 56. 142



I hope this makes sense. .

When I tried using SA 2003 the error was the same all over town. Can anyone chech these locations on their software? Thanks.

 

[HC]

Well, the good news is I don't think you're crazy.



The bad news is, I think you've identified one of those rare errors in the map databases, and you're lucky enough that it is right in your hometown. When I enter the coordinates you gave me into MapQuest, it shows me at the correct street intersection. But all of the roads on DeLorme near Ceres, and even down the road in Keyes, appear to be in error by the ~0. 25 miles you reported.



I tried to find a location where the MapQuest and DeLorme maps agreed - the first one I found was up in Manteca, at the corner of Yosemite and Main. If you start driving around, I'm sure at some point you'll find you're tracking right on the road; but since I have to make multiple map comparisons it's harder for me to see exactly how far the region of "incorrect locations" extends.



I've sent an e-mail to DeLorme to notify them of the problem; if there is a downloadable "patch" I'll let you know.



I guess the bright side is, you're not doing anything wrong, and when you go on a longer trip, the problem will "self correct" as soon as you leave the Twilight Zone where you now live.

 

[shoveljunk]

Message to HC

Did you get the PM I sent you at the time of the globle crash on the eve of the 24th?