Accuracy

[Buggy5151]

I have a Garmin Vista and I'm always 20 to 30 feet away from the Cache

that I'm hunting for.

Is this normal or is my Gps set up wrong ?

[WH]

Many things can effect GPS accuracy. The first thing you should check is to make sure the datum is set to WGS84. Accuracy issues can also be caused by tree cover and how accurate the hider was with their coordinates.

 

On the other hand 20' - 30' accuracy isnt all that bad.

[+New England n00b]

I have the step down version (Legend) and get that kind of accuracy routinely. (By step down, I don't mean lesser ability - the Vista has some extra stuff like a compass, altimeter and more memory, the rest of the guts are the same...)

Edited August 20, 2004 by New England n00b

[+YuccaPatrol]

If you are 20-30 feet from the cache, then your GPS is working perfectly.

[+Robespierre]

Today, the lock was good for my Vista, and no tree cover, for a micro. I was down to about 8' accuracy, but a bad day would be 50', and a normal day, 25-30'. Relax.

[Tahosa and Sons]

Normal lock on is around 15ft. with wass I've done 6 ft.

[+briansnat]

And remember, even if your unit is perfectly accurate, the placer's unit may have had an error. Anything under 50 feet is normal for a consumer grade GPS.

Edited August 20, 2004 by briansnat

[+strikeforce1]

  Anything under 50 feet is normal for a consumer grade GPS.

Except for hunting Micros (in the dark) Night Caching. It's a whole new deal then. You can up the difficulty about 10 stars.

 

I avg. 13-25 ft with a Garmin 12 and Etrex Legend, side by side 9/10 x's . SF1

[+Thot]

I have a Garmin Vista and I'm always 20 to 30 feet away from the Cache that I'm hunting for.

 

Is this normal or is my Gps set up wrong ?

Recently I asked people here to estimate the average distance their GPS puts them from the cache. Averaging the nearly 25 replies as best I could, I concluded if you're normally getting within 18-25 feet you're about typical. I assume you understand that the distance can be greater or less than the average and under some conditions the distance can fairly large. If you run into a distance of more than about 50 feet then somebody probably made a mistake.

Edited August 21, 2004 by Thot

[+Sam Stone]

I am very new to GPSing and geocaching and I am glad I stumbled upon this neat sport, however I too have troubles with my Vista leading me down the wrong garden path every so aften.

 

I was wondering if this next example was normal for a gps. I marked a waypoint, walked away a few feet, went back to the same spot and marked another one, and did this 5 times. When I used the "find nearest waypoint" and "goto" feature it didnt pick the same waypoint every time, in fact it went through them all and I was at least 50 feet in error. The next day I did a "goto nearest waypoint" and it was 400 feet away. Any ideas?

[+Robespierre]

Do you have a cockatoo named Misty?

[+briansnat]

I am very new to GPSing and geocaching and I am glad I stumbled upon this neat sport, however I too have troubles with my Vista leading me down the wrong garden path every so aften.

 

I was wondering if this next example was normal for a gps. I marked a waypoint, walked away a few feet, went back to the same spot and marked another one, and did this 5 times. When I used the "find nearest waypoint" and "goto" feature it didnt pick the same waypoint every time, in fact it went through them all and I was at least 50 feet in error. The next day I did a "goto nearest waypoint" and it was 400 feet away. Any ideas?

50 feet away is normal. 400, no. Did you have a good sat lock each time?

[+AtoZ]

YES IT IS NORMAL. The GPS is not that accurate unless you make a big investment, like 5 to 10k. So 20 to 30 feet is good. If you have WAAS then maybe down to 10ft if the wind is blowing the right way, LOL. But 20 to 30 feet is pretty good.

cheers

[+Thot]

I marked a waypoint, walked away a few feet, went back to the same spot and marked another one, and did this 5 times. When I used the "find nearest waypoint" and "goto" feature it didnt pick the same waypoint every time, in fact it went through them all and I was at least 50 feet in error. The next day I did a "goto nearest waypoint" and it was 400 feet away.

Something is clearly wrong with 400 ft difference. Are you allowing the device to have a little time to settle after you get near the target?

 

Soon after I started blindleader & EScout suggested I find some stable benchmarks near me and go to them a few times to see how the gadget behaves when you know you have accurate coordinates.

 

Here are EScout's comments:

 

"[T]here are super accurate benchmarks that are listed to one-hundred thousandths of a second. They are called adjusted (they are GPS adjusted.) This is an excellent way to test your GPSr and get confidence on its accuracy. (The stated "accuracy" on some GPSrs is really an "estimated position error." I think you may be pleasantly surprised when you go to one of these marks, like I have been when testing my GPSrs.

 

Datasheets

 

Go to this website, choose your state, county, GPS sites only. Sort by Lat or Long and then choose a disk or rod (not a CORS.) Lots of these are on public streets and other easily accessible areas ( Remember, if you enter the coords of the benchmark into your GPSr, you need to round off, so you will be within about a 3 foot diameter of the mark. Simple geometry will let you find the position of your rounded coords (one thousandth of a minute is about 6 feet in latitude.)"

 

I think this is good advice. Lower accuracy benchmarks can be way off. I looked for benchmarks that were stability class A, if you don't find any try B. Hoping it is near you, go to it a few times so you see how things vary from time to time.

 

I was surprised how close my unit came to the real coordinates. A friend with an identical unit went with me once and got almost the same reading as I did.

 

This exercise gave me a feeling of confidence about how to use the gadget.

 

Then, when on a hunt you must remember the person who placed the cache may not have been careful in measuring the location.

Edited August 23, 2004 by Thot

[+Sam Stone]

Thanks for the tips everyone and no, I don't have a bird called Misty, lol. Thot, I was excited to try that benchmark idea but unfortunately it doesn't list any places in Canada. Do you know if there is such a website?

[+ShowStop]

  Anything under 50 feet is normal for a consumer grade GPS.

Except for hunting Micros (in the dark) Night Caching. It's a whole new deal then. You can up the difficulty about 10 stars.

 

I avg. 13-25 ft with a Garmin 12 and Etrex Legend, side by side 9/10 x's . SF1

What are you trying to say? I night cache all the time. One you get into the groove, it becomes much easier to find the caches. Now micros hidden in a bush or tree are a real PITA...

[+Kai Team]

I have the eTrex Vista and agree with all of the earlier comments (20 ft is normal, 6-7 feet is best with WAAS enabled and a clear sky). I wanted to add two things that I've found helpful:

 

1) You can display the GPS accuracy on the Vista's navigation screen, which is very helpful when caching (it tells you how far off you might be!). Choose the navigation screen from the menu. Once on the navigation screen, use the "Click Stick" to go down to one of the two little windows at the bottom of the screen. With either of the little windows highlighted, click the click stick and use it to choose and select "GPS Accuracy". The accuracy of your unit, which changes with different terrain conditions, will now show in that little window (I keep "GPS Accuracy" in the lower left window and "Speed" in the lower right, since speed determines whether you are getting an accurate bearing from the GPS or are relying on the electronic compass, which I find rather unreliable).

 

2) What Sam Stone was talking about a few posts up is almost what's called "waypoint averaging" - i.e. I marked a waypoint, walked away...went back to the same spot and marked another one, and did this 5 times. It is a very good practice when you place a cache, to reduce the error in your posted coordinates (mark 3-5 waypoints, walking away and coming back between each one, then average them by adding the numbers to the right of the last decimal point together and dividing by the number of waypoints you're averaging).

 

If the person who hid the cache used waypoint averaging and you know how accurate your GPSr is at the moment you're approaching the posted coordinates, you'll have a much better idea of how close (or far away) the cache could be!

[+Sam Stone]

Thanks for the tip Kai team, I'll try averaging next time.

[+Hard Oiler]

Thanks for the tips everyone and no, I don't have a bird called Misty, lol. Thot, I was excited to try that benchmark idea but unfortunately it doesn't list any places in Canada. Do you know if there is such a website?

Lots in Canada (and a few with caches at them for checking your GPS). Let me know where you are in Canada and we'll find one for you.

[+fly46]

Another thing, Sam, GPSrs need a chance to 'settle' - that is... it's almost like they need to catch up to your movement. It's fine to triangulate when placing a cache, but you shouldn't just run up to the spot, save the cords, and rush to the next direction... In fact, even better than triangulating - wait for a good, clear day, take the GPS to the spot you want it in, and then leave it there, nice and flat, for about five minutes. You'll have better cords with patience than with anything else.

 

If you're out on the trail and off, just stand still for a little bit - watch the numbers - when they quit moving while you're standing still, it's 'settled'.

[+AtoZ]

I went to a cache I placed this week end and it seemed I was way off but I had full WAAS and when I measured the distance it was only 2.65 meters. That is pretty good but when your looking it seemed a long ways off. But 20 to 30 feet is normal without WAAS.

Cheers

[Major Catastrophe]

I know someone's gonna disagree, but IMO all consumer-grade GPS receivers are practically identical. They all use (obviously) the same satellites, along with similar algorithms to process the information and suffer from similar problems. With some minor differences due to antenna construction and bells and whistles, they are functionally the same. On a good day with an ideal satellite constellation any of them will take you to within a couple of feet of a spot. On a bad day you might as well be looking in the next county because it will take you there anyway!

[kayaman]

 

Go to this website, choose your state, county, GPS sites only. Sort by Lat or Long and then choose a disk or rod (not a CORS.)

how do you know if it is a disk or rod ????

[+EScout]

Accuracy is how close you are to a known place on earth. What is shown on your GPSr screen is "Estimated Position Error", which is what it sounds like, and called "Accuracy" on Garmins.

I recommend the Adjusted Benchmarks because you can see how accurate your GPSr is, and compare it to what it says on the screen.

Here is a listing for one, the type of mark is after the word,"Marker:

The coords are in minutes and seconds.

 

National Geodetic Survey, Retrieval Date = AUGUST 24, 2004

DY1768 ***********************************************************************

DY1768 DESIGNATION - Z 50 RESET

DY1768 PID - DY1768

DY1768 STATE/COUNTY- CA/LOS ANGELES

DY1768 USGS QUAD - TORRANCE (1981)

DY1768

DY1768 *CURRENT SURVEY CONTROL

DY1768 ___________________________________________________________________

DY1768* NAD 83(1994)- 33 46 52.89299(N) 118 17 47.04124(W) ADJUSTED

DY1768* NAVD 88 - 21.030 (meters) 69.00 (feet) ADJUSTED

DY1768 ___________________________________________________________________

DY1768 EPOCH DATE - 1995.00

DY1768 X - -2,515,583.035 (meters) COMP

DY1768 Y - -4,672,647.944 (meters) COMP

DY1768 Z - 3,526,306.861 (meters) COMP

DY1768 LAPLACE CORR- 1.62 (seconds) DEFLEC99

DY1768 ELLIP HEIGHT- -14.89 (meters) (11/30/95) GPS OBS

DY1768 GEOID HEIGHT- -35.90 (meters) GEOID03

DY1768 DYNAMIC HT - 21.008 (meters) 68.92 (feet) COMP

DY1768 MODELED GRAV- 979,605.8 (mgal) NAVD 88

DY1768

DY1768 HORZ ORDER - FIRST

DY1768 VERT ORDER - FIRST CLASS II

DY1768 ELLP ORDER - FOURTH CLASS II

DY1768

DY1768.The horizontal coordinates were established by GPS observations

DY1768.and adjusted by the National Geodetic Survey in November 1995.

DY1768.This is a SPECIAL STATUS position. See SPECIAL STATUS under the

DY1768.DATUM ITEM on the data sheet items page.

DY1768.The horizontal coordinates are valid at the epoch date displayed above.

DY1768.The epoch date for horizontal control is a decimal equivalence

DY1768.of Year/Month/Day.

DY1768

DY1768.The orthometric height was determined by differential leveling

DY1768.and adjusted by the National Geodetic Survey in June 1995.

DY1768.WARNING-Repeat measurements at this control monument indicate possible

DY1768.vertical movement.

DY1768

DY1768.The X, Y, and Z were computed from the position and the ellipsoidal ht.

DY1768

DY1768.The Laplace correction was computed from DEFLEC99 derived deflections.

DY1768

DY1768.The ellipsoidal height was determined by GPS observations

DY1768.and is referenced to NAD 83.

DY1768

DY1768.The geoid height was determined by GEOID03.

DY1768

DY1768.The dynamic height is computed by dividing the NAVD 88

DY1768.geopotential number by the normal gravity value computed on the

DY1768.Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45

DY1768.degrees latitude (g = 980.6199 gals.).

DY1768

DY1768.The modeled gravity was interpolated from observed gravity values.

DY1768

DY1768; North East Units Scale Factor Converg.

DY1768;SPC CA 5 - 531,251.096 1,972,545.440 MT 1.00006414 -0 10 08.2

DY1768;SPC CA 5 - 1,742,946.30 6,471,592.83 sFT 1.00006414 -0 10 08.2

DY1768;UTM 11 - 3,738,669.062 379,970.442 MT 0.99977761 -0 43 15.3

DY1768

DY1768! - Elev Factor x Scale Factor = Combined Factor

DY1768!SPC CA 5 - 1.00000234 x 1.00006414 = 1.00006648

DY1768!UTM 11 - 1.00000234 x 0.99977761 = 0.99977995

DY1768

DY1768 SUPERSEDED SURVEY CONTROL

DY1768

DY1768 NAVD 88 (06/15/91) 21.044 (m) 69.04 (f) UNKNOWN 1 2

DY1768 NGVD 29 (??/??/92) 20.305 (m) 66.62 (f) ADJ UNCH 1 2

DY1768

DY1768.Superseded values are not recommended for survey control.

DY1768.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums.

DY1768.See file dsdata.txt to determine how the superseded data were derived.

DY1768

DY1768_U.S. NATIONAL GRID SPATIAL ADDRESS: 11SLT7997038669(NAD 83)

DY1768_MARKER: DB = BENCH MARK DISK

DY1768_SETTING: 31 = CURB

DY1768_STAMPING: Z 50 1926 RESET 1945

DY1768_MARK LOGO: CGS

DY1768_MAGNETIC: N = NO MAGNETIC MATERIAL

DY1768_STABILITY: D = MARK OF QUESTIONABLE OR UNKNOWN STABILITY

DY1768_SATELLITE: THE SITE LOCATION WAS REPORTED AS SUITABLE FOR

DY1768+SATELLITE: SATELLITE OBSERVATIONS - April 28, 1999

DY1768

DY1768 HISTORY - Date Condition Report By

DY1768 HISTORY - 1945 MONUMENTED CGS

DY1768 HISTORY - 1946 GOOD NGS

DY1768 HISTORY - 1968 GOOD CA-037

DY1768 HISTORY - 1978 GOOD NGS

DY1768 HISTORY - 19890601 GOOD NGS

DY1768 HISTORY - 19940722 GOOD NGS

DY1768 HISTORY - 19941116 GOOD MWDSC

DY1768 HISTORY - 19950406 GOOD MWDSC

DY1768 HISTORY - 19990428 GOOD NGS

DY1768

DY1768 STATION DESCRIPTION

DY1768

DY1768'DESCRIBED BY NATIONAL GEODETIC SURVEY 1946

DY1768'AT WILMINGTON.

DY1768'AT WILMINGTON, NEAR THE INTERSECTION OF GAFFEY STREET AND

DY1768'ANAHEIM STREET, IN LARGE CONCRETE BRIDGE OVER STREET CAR TRACKS,

DY1768'AT THE SOUTH-WEST CORNER OF THE BRIDGE, 0.5 FOOT SOUTHWEST

DY1768'OF THE SOUTHWEST CURB OF BRIDGE, ON TOP OF THE SIDEWALK.

DY1768'A STANDARD DISK, STAMPED Z 50 1926 RESET 1945.

DY1768

DY1768 STATION RECOVERY (1968)

DY1768

DY1768'RECOVERY NOTE BY LOS ANGELES COUNTY CALIFORNIA 1968

DY1768'RECOVERED IN GOOD CONDITION.

DY1768

DY1768 STATION RECOVERY (1978)

DY1768

DY1768'RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1978

DY1768'RECOVERED IN GOOD CONDITION.

DY1768

DY1768 STATION RECOVERY (1989)

DY1768

DY1768'RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1989

DY1768'RECOVERED IN GOOD CONDITION.

DY1768

DY1768 STATION RECOVERY (1994)

DY1768

DY1768'RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1994 (SDD)

DY1768'IN LOS ANGELES (HARBOR CITY AREA) , AT THE INTERSECTION OF GAFFEY AND

DY1768'ANAHEIM STREETS, IN TOP OF AND 0.3 M (1.0 FT) SOUTHEAST OF THE

DY1768'NORTHWEST END OF THE SOUTHWEST CONCRETE CURB OF THE ANAHEIM STREET

DY1768'BRIDGE SPANNING A CREEK, 49.5 M (162.4 FT) NORTHEAST OF THE CENTERLINE

DY1768'OF THE NORTHBOUND LANES OF GAFFEY STREET, 7.3 M (24.0 FT) SOUTHWEST OF

DY1768'THE CENTERLINE OF ANAHEIM STREET, 0.6 M (2.0 FT) NORTHEAST OF THE

DY1768'NORTHWEST END OF THE BRIDGE GUARDRAIL, AND 0.2 M (0.7 FT) ABOVE THE

DY1768'LEVEL OF ANAHEIM STREET.

DY1768

DY1768 STATION RECOVERY (1994)

DY1768

DY1768'RECOVERY NOTE BY METRO WATER DISTR SO. CALIFORNIA 1994 (DEL)

DY1768'LOMITA, NEAR THE INTERSECTION OF ANAHEIM ST, PALOS VERDES DRIVE NORTH,

DY1768'GAFFEY ST AND VERMONT AVE. ON ANAHEIM ST 350 FEET (106.7 M) EASTERLY

DY1768'OF VERMONT AVE, 27 FEET (8.2 M) SOUTHERLY OF ANAHEIM ST, 0.7 FEET

DY1768'(21.3 CM) EASTERLY OF THE WEST END OF THE BRIDGE WALKWAY THAT LIES ON

DY1768'THE SOUTHERLY SIDE OF ANAHEIM ST, A 3-1/2 INCH BRASS DISK STAMPED

DY1768'RESET Z-50 1926 SET FLUSH IN CONCRETE CURB OF BRIDGE SPANNING CREEK.

DY1768'REF MWD FB 2519 02 024, TB 794 A6.

DY1768

DY1768 STATION RECOVERY (1995)

DY1768

DY1768'RECOVERY NOTE BY METRO WATER DISTR SO. CALIFORNIA 1995 (DEL)

DY1768'RECOVERED AS DESCRIBED.

DY1768

DY1768 STATION RECOVERY (1999)

DY1768

DY1768'RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1999 (GAS)

DY1768'IN HARBOR CITY, AT THE INTERSECTION OF GAFFEY AND ANAHEIM STREETS, IN

DY1768'TOP OF AND 0.3 M (1.0 FT) SOUTHEAST OF THE NORTHWEST END OF THE

DY1768'SOUTHWEST CONCRETE CURB OF THE ANAHEIM STREET BRIDGE SPANNING A CREEK,

DY1768'49.5 M (162.4 FT) NORTHEAST OF THE CENTERLINE OF THE NORTHBOUND LANES

DY1768'OF GAFFEY, 7.3 M (24.0 FT) SOUTHWEST OF THE CENTERLINE OF ANAHEIM, 0.1

DY1768'M (0.3 FT) NORTHEAST OF THE NORTHWEST END OF THE BRIDGE RAIL, AND 0.2

DY1768'M (0.7 FT) ABOVE THE LEVEL OF THE STREET. NOTE--THE MARK IS ON STREET

DY1768'RIGHT-OF-WAY.