Jump to content
Sign in to follow this  
Followers 2
traildad

Looking for Benchmark

Recommended Posts

I would like to test my GPSr against a known verified spot. How can I find a Benchmark near my home that I can use? I live near here N 38° 21.718 W 121° 57.088 and I would like to find one close to me. What should I be searching for to be sure it is a verified GPS accurate Benchmark?

Share this post


Link to post

What you want to look for is one with adjusted coordinates (as oposed to scaled coordinates). A nearby example is JS3866. Should be a short drive from you down to the airport parking lot. Best yet people have found it and posted pictures for you on the geocaching website.

 

Most commercial handheld GPSrs won't do much better then 12-15 feet of accuracy given an unobstructed view of the sky. The military and certain government entities are the only ones that have full access to the GPS system that allows them to get subfoot accuracy.

 

Happy hunting and welcome to benchmarking!

Share this post


Link to post

What you want to look for is one with adjusted coordinates (as oposed to scaled coordinates). A nearby example is JS3866. Should be a short drive from you down to the airport parking lot. Best yet people have found it and posted pictures for you on the geocaching website.

 

Most commercial handheld GPSrs won't do much better then 12-15 feet of accuracy given an unobstructed view of the sky. The military and certain government entities are the only ones that have full access to the GPS system that allows them to get subfoot accuracy.

 

Happy hunting and welcome to benchmarking!

Ok great. I have a Magellan Meridian Gold and it lost WAAS recently. There was some discussion about WAAS and if it makes a difference in accuracy. A fix for this problem has been found now and I am curious to see what difference it makes. I have two Meridian Golds and only one has been fixed. I plan to place both of them on the Benchmark and see how their readings compare. Thanks for the help on the Benchmark. That is near my house. I also have my one and only Benchmark find (a FTF) near there. Thanks again.

Share this post


Link to post
What you want to look for is one with adjusted coordinates (as oposed to scaled coordinates). A nearby example is JS3866. Should be a short drive from you down to the airport parking lot. Best yet people have found it and posted pictures for you on the geocaching website.

Having an easy-to-find benchmark with adjusted coordinates is good, but what's even better is that he'll be within easy walking distance of Fenton's. :angry: On the other hand, he apparently lives just across 80 from the Nut Tree anyway, so a visit to Fenton's probably isn't a special event for him.

 

Patty

(who still hasn't made it to the new Nut Tree yet)

Share this post


Link to post

I would like to test my GPSr against a known verified spot. How can I find a Benchmark near my home that I can use? I live near here N 38° 21.718 W 121° 57.088 and I would like to find one close to me. What should I be searching for to be sure it is a verified GPS accurate Benchmark?

 

In our part of the state, its my understanding that certain benchmarks with PIDs that begin with an "A" (e.g., AC9891) will refer you to benchmarks which have been "occupied as part of a California HPGN Densification Survey".

 

Data generated from those types of 'stations' were processed in such a way as to "obtain the highest precision possible" and the coordinate data were obtained by satellite observations. The HPGN benchmark disks that I've recovered (discovered) have all been of Aluminum construction instead of the ubiquitous "brass" type. Here is an example image of such a disk...

b966b9e8-ced6-436a-830a-571c6b8613ad.jpg

 

Here is an example of one geocache that utilizes such a survey station, note all of the log entries include individual GPS readings so that you can see how our 'general purpose' GPS devices compare to the 'professional grade' systems.

Share this post


Link to post
What you want to look for is one with adjusted coordinates (as oposed to scaled coordinates). A nearby example is JS3866. Should be a short drive from you down to the airport parking lot. Best yet people have found it and posted pictures for you on the geocaching website.

Having an easy-to-find benchmark with adjusted coordinates is good, but what's even better is that he'll be within easy walking distance of Fenton's. :angry: On the other hand, he apparently lives just across 80 from the Nut Tree anyway, so a visit to Fenton's probably isn't a special event for him.

 

Patty

(who still hasn't made it to the new Nut Tree yet)

I think I heard that the Old Nut Tree part of the New Nut Tree went out of business already. :D

Share this post


Link to post

 

In our part of the state, its my understanding that certain benchmarks with PIDs that begin with an "A" (e.g., AC9891) will refer you to benchmarks which have been "occupied as part of a California HPGN Densification Survey".

 

 

Interesting observation.

 

There are 2,535 marks in the NGS database in the state of California that have a PID that begins with the letter A. Only 1,118 of those have adjusted positions.

 

However your odds improve if you narrow the search to marks whose PIDS start with AC. There are 119 of those of which 103 have adjusted positions.

Share this post


Link to post
I think I heard that the Old Nut Tree part of the New Nut Tree went out of business already. :angry:

By "Old Nut Tree part," you mean the rides area, right? I knew about that, but aren't the shops and restaurants (including Fenton's ice cream) still open?

 

Patty

Share this post


Link to post
I have two Meridian Golds and only one has been fixed. I plan to place both of them on the Benchmark and see how their readings compare.

 

Hi, TrailDad,

 

Instead of placing the units on top of the disk, hold one in each hand, while standing over the benchmark. Keep them at least one foot apart. (Two feet is better.) Visualize the GPS unit as a radio receiver. It needs a clear view of the sky in order to receive the maximum number of satellites and workable signal strengths.

 

Don't worry about being exactly over the disk. Distances of several inches will have no impact upon your results.

 

You can obtain more precise results by starting the test about 15 feet from the benchmark. Allow the GPS readings to stabilize. Then walk over to the disk and stop. Note the readings, and then repeat this from another direction--at least 90 degrees from the first. This tests the units for their abilities to reproduce results. (This also is a good method for determing the coordinates of a cache you have just placed.)

 

I'm curious about the WAAS problem. Did your individual units fail, or is this something related to that particular brand of GPS receiver?

 

-Paul-

Share this post


Link to post

Ok great. I have a Magellan Meridian Gold and it lost WAAS recently. There was some discussion about WAAS and if it makes a difference in accuracy. A fix for this problem has been found now and I am curious to see what difference it makes. I have two Meridian Golds and only one has been fixed. I plan to place both of them on the Benchmark and see how their readings compare. Thanks for the help on the Benchmark. That is near my house. I also have my one and only Benchmark find (a FTF) near there. Thanks again.

 

If you have a clear view of the sky you can set the GPSr on the disk.

 

The picture shown has the GPSr showing the distance to go. We did a goto for the given coordinates of that benchmark to see how accurate our unit would be. It shows we are 2 feet from the benchmark. We found that walking at a slow pace allows the GPSr to accurately show our position and when we reach the target our units show very good accuracy.

 

8731629d-b748-45dc-83fa-60de0ac6ce6e.jpg

 

FQ0581

 

John

Share this post


Link to post
I think I heard that the Old Nut Tree part of the New Nut Tree went out of business already. :)

By "Old Nut Tree part," you mean the rides area, right? I knew about that, but aren't the shops and restaurants (including Fenton's ice cream) still open?

 

Patty

Yes I mean the rides. I just might check out Fentons when I go to the Airport.

Share this post


Link to post
I have two Meridian Golds and only one has been fixed. I plan to place both of them on the Benchmark and see how their readings compare.

 

Hi, TrailDad,

 

I'm curious about the WAAS problem. Did your individual units fail, or is this something related to that particular brand of GPS receiver?

 

-Paul-

When they changed WAAS Satellites the GPSr was automatically updated to use the new ones. With a lot of the older Magellan units you were good to go unless you, didn't turn your unit on while the changes were being broadcast, or if you did a clear all memory, or if you reinstalled your firmware. The unit would default back to the satellite numbers written in the firmware code. Some people figured out where the numbers were written in the firmware code and were able to help everyone fix the problem permanently. With two easy changes with a text editor I was able to code in the correct WAAS sattelites numbers. Thanks to Trainlove and qwert1515 in the Magellan Meridian Yahoo Group for helping us.

Share this post


Link to post

Just as a trivial aside: I think it has been established that the WAAS corrections are actually ITRF values. In some areas of the country those have shifted up to several meters from NAD83(86) published values. Now usually those 1-2 meters are indistinguishable with recreational grade GPS units. You may be able to pick it up with long time averages, AND if you can get a more precise position out of your receiver than is usually displayed. So your WAAS position theortically will not match the published control coordinates.

 

There must be a transformation tool on the NGS site to convert. ITRF positions are time dependent.

 

- jlw

Share this post


Link to post
...ITRF values. In some areas of the country those have shifted up to several meters from NAD83(86) published values.

Got an example?

Share this post


Link to post

How far off is a scaled bench mark? I am knew to geo-c and I thought i would go out and locate a few bench marks close to my house this afternoon.. But i couldn't find either one.. I chalked it up to being a rookie till i read this thread and come to find out both of the ones i was looking for today are SCALED...

 

One of the ones i was looking for the coordinates were about two city block off of the description.. the other i gave up on early because it look dangerous to take the kids with me across the territory so we left and went looking for a easy cache at a local park...

Share this post


Link to post

Hi tleslie79072:

Welcome to Benchmark hunting. Scaled benchmarks are very often, even usually, not accurately located in horizontal position (Latitude & Longitude). They can easily be 600 feet off. They ARE accurate in elevation (vertical location). The GPS will just get you in the general neighborhood.

 

For checking a GPS accuracy you must have a Triangulation Station, which have adjusted positions. In the NGS terminology, adjusted means it is an accurate position.

Share this post


Link to post

Hi, tleslie79072,

 

As previously stated, you must rely on the description to get you to a benchmark with SCALED horizonal coordinates. Once you become accustomed to the unusual sentence structure and terminology, looking for the "clues" becomes a lot of fun. And it forces the hunter to stop and "get his/her bearings", so to speak, rather than rushing into a situation. It's a great concept to convey to children, and in truth, we adults could benefit from applying this in our daily lives!

 

Here are some of the clues, and what they look like, physically:

 

*Reference Tag. An aluminum triangle attached to an object such as a fence post or power pole.

 

*PP and TP. Power pole or telephone pole. (Xfmr is a pole-mounted transformer on a power pole.)

 

*Brace Pole. A pole erected to serve as an above-ground anchor for a guy wire.

 

*Drop Pole. A pole with telephone or electrical wires arriving on one side, but not leaving; or a pole erected for the sole purpose of supporting a long run of wire from a pole to a distant building.

 

*Guy Wire. A slanting wire from a pole to an anchor buried in the ground. (Measurements are from the point where the wire meets the ground.)

 

*C/L. Centerline of the road. It is not necessarily where the "yellow line" is, especially if there are turn lanes present. Look up and down the road to visualize where the center would be without turn lanes and medians.

 

*Other references generally are obvious, but it is very helpful to have a compass to determine which corner of a building is the southwest corner. Watch for subtle changes in the color or composition of building materials, which might indicate an addition. (Look for the original southwest corner.)

 

*Hint: Reference tags fall off of trees as the tree grows.

 

*Witness Post. A small metal sign on a pole, reading "Do not disturb nearby survey marker", or the newer version which is a 4-foot tall, slender, flexible marker--usually orange or yellow. The term also is applied to those vertical orange plastic pipes you see near underground telephone and cable television wiring. (It is common to find that the metal witness post has fallen or is gone. Over many years, the pole rusts and breaks, or mowers hit it.)

 

*Hint: Wooden power poles get replaced, over long periods of time. Often, this involves a significant repositioning to accommodate road widening. Double-pole supports for high-voltage lines may have been replaced by a single metallic monopole. Any change to a pole affects the reference in some way.

 

Here are some time-tested techniques: When you get out of the vehicle, pause and check your compass to determine North. Then begin reading the description and looking around to see which objects still exist. Read the descriptions from the bottom, where the newest ones are found. Also, read the descriptions "backward", since the closest objects usually are listed last.

 

I hope this is helpful. Finding SCALED benchmarks can be the most interesting part of the hobby!

 

-Paul-

Share this post


Link to post

 

I'm curious about the WAAS problem. Did your individual units fail, or is this something related to that particular brand of GPS receiver?

 

-Paul-

 

Magellan Problem

 

I was unaware there was a fix for this so appreciate the thread.

Share this post


Link to post

I'll be another to move off topic.

I haven't heard of the Old or New or New/Old parts of the Nut Tree - I haven't been there in over 20 years.

When I was a kid in the Bay Area my father would venture to Reno a lot on Army Reserve Duty. He would always stop and buy us gingerbread men from Nut Tree. Fond memories of that.

 

So, with the new and old etc I suppose it's had development like my other favorite roadside stand turned into a near mega corporation - Casa de Fruta.

 

I've got two Magellan Meridians, a gold and a platinum. I'll have to check into andy WASS problems.

Share this post


Link to post

Rumpled (or anyone else):

 

PM me if any problem with getting your Meridian re-WAAS'd. My Meridian is all better now.

 

Also, if you still have WAAS, check your time vs another unit or WWV, or USNO on line. If more than a minute or so off, you have the Meridian "time warp" problem, which will effect accuracy. The fix is a 'Reset All". Then you loose WAAS, and need the re-WAAS fix. Ahhh... The joys of supporting a "legacy" Magellan unit, which is anything from Magellan more than 6 months old, right? :D

Share this post


Link to post

I'll be another to move off topic.

I haven't heard of the Old or New or New/Old parts of the Nut Tree - I haven't been there in over 20 years.

When I was a kid in the Bay Area my father would venture to Reno a lot on Army Reserve Duty. He would always stop and buy us gingerbread men from Nut Tree. Fond memories of that.

 

So, with the new and old etc I suppose it's had development like my other favorite roadside stand turned into a near mega corporation - Casa de Fruta.

 

I've got two Magellan Meridians, a gold and a platinum. I'll have to check into andy WASS problems.

The original Nut Tree closed long ago. Recently it has been redone as a large shopping center with a few rides left over from the original. Now it is Best Buy, Borders Books, Sports Authority etc. along with several restaurants.

Share this post


Link to post

I did a quickie test Sunday. I was having some difficultly getting WAAS to work. I am not sure how exactly NAD83 affected what I was trying to do. I figure to make a good job of it I will need to try this several times with WAAS activated on first one then the other unit to eliminate possible errors from the individual unit. Test one started out showing the non WAAS as being about 6 feet off and the WAAS unit around 13 feet off. I am not sure how long I would need to stand there to get a true WAAS average, but for Geocaching we don't stand at the cache all day so I will keep it short.

Share this post


Link to post

NAD 83 gives us the coordinates of a control point where it was 26 years ago. Due to slow continental drift, wouldn't today's coordinates differ by as much as a few feet, depending on your location?

Edited by wbf pls

Share this post


Link to post

wbf pls:

 

Simple answers:

1) NAD83 is a Datum (a "reference system" if you will). It does not mean that the positions taken using it are from 1983.

2) NGS benchmark positions are periodically adjusted to improve their locations, based on newer data taken nearby. This is a gross simplification, but the point is that they are kept up to date.

3) I think NGS benchmarks are adjusted to take into consideration continental drift (not sure - experts?)

4) Regardless of 3) above, our handheld GPS receivers are not anywhere near accurate to be concerned about continental drift, unless you plan to be around in 10,000 years or so.

 

I have a suspicion there are others out there who may want to amplify on the above very simple summary. Have at it!

Share this post


Link to post

What wbf pls is saying is basically what I tried to say in my post of a few days ago. It is more like plate tectonics that are starting to be taken into account in the various geodetic reference systems.

 

There is always a tension between the ability to measure and quantify the actual precise global relationship between points which is now possible with high precision GPS techniques, and having accurate relative positions and stable positions and coordinates of points on the ground.

 

In the old days such as NAD27 the coordinates were tied to lower precision coordinate determination methods and constrained to the derivation of coordinates based solely on terrestrial conventional observations. They never changed.

 

About the time NAD83 was first published, the ability to detect drifts in local areas was starting to be ovservable with GPS measuring technology and was creating problems in defining coordinates that were scientifically accurate over large distances woth the advent of modern GPS technology.

 

We now know that the earth moves at various rates in various parts of the country and globally with respect to other continents.

 

Until recently a station with NAD83 coordinates would remain fixed, but with respect to global reference systems like ITRF it was changing. If you did a GPS Opus session or used the CORS stations to process survey grade GPS you would see reports in the two systems where the ITRF was moving away from the NAD83 values.

 

We now have datum and epoch. That is the datum which represents the reference system ellipsoid and base, and the epoch represents the date that the point or local network coordinate was computed. Most of CORS is NAD83(96) I think. So that means as of the adjustment of 1996.

 

NGS made the decision recently to cut NAD83 loose and let it move with the earth, so there may be future data sheets with newer epochs reported, or surveys with newer epochs reported.

 

The movement is on the order of a few mm's per year but over time adds up to a few feet and depends on where you are.

 

The basic recreational grade GPS unit is NOT usually able to detect these small changes. It's solution would be based on the native almanacs that the satellites transmit and the assumptions about that coded into your receiver.

 

WAAS provides differential corrections based upon stations that were positioned to ITRF coordinates at a certain point in time, and thus those corrections will end up changing the coordinates your receiver computes ever so slightly due to the fact that ITRF coordinates shifted with time based on the plate tectonics shifts as of the date that the WAAS stations were positioned.

 

So if you had the perfect GPS receiver that could accurately compute and report position to 0.01 of a second or better, the WAAS position would differ from the data sheet by a small amount, generally no worse than a few feet off from NAD83 positions as represented by the data sheets.

 

That is about the limit of my comprehension of the subject.

 

It would be very hard to really check your GPS except in the most crude way by sitting on an existent monumented horizontal control point. If you try to do that with say 4 minute averages over several hours or days you will see that although your GPS receiver may report that it is good to 5 feet or so, you will find that your positions actually vary by up to several meters even with WAAS on. In the woods it can be 3 or 4 times worse. WAAS cannot model local conditions and errors which affect your receiver.

 

= jlw

Edited by jwahl

Share this post


Link to post
WAAS cannot model local conditions and errors which affect your receiver.

Very well said......and one of the "local conditions" we tend to overlook is signal reflection from nearby objects--especially large, flat metallic surfaces such as highway signs, bridge abutment warning markers, steel-supported buildings, etc. When possible, position yourself at an angle, or perpendicular to the metal object, when taking a GPS reading.

 

-Paul-

Share this post


Link to post

Here's a collection of info about Horizontal Time Dependent Positioning. It would appear urgent that you understand this stuff if you are a surveyor in California, and probably required all over the US at the finest levels of accuracy.

 

Probably irrelevant to recreational (consumer) grade GPS even in California, over a span of 26 years.

 

I've gotten headaches from trying to read other stuff about datum shifts and plan to attack this list next to see if it makes things any clearer. Jerry's comments in plain English may help me understand some of what I've read on the next pass through it.

 

Here's are articles that may be of interest about getting the best results from your handheld.

Edited by Bill93

Share this post


Link to post

Wow! I'm moving Northwest faster than I thought! 35 to 40mm per year. Whew. I thought it was a couple mm per year. Wow. And if the San Andreas faults lets loose, it could be many feet all at once (if I'm still alive to talk about it)!

Share this post


Link to post

 

That is about the limit of my comprehension of the subject.

 

It would be very hard to really check your GPS except in the most crude way by sitting on an existent monumented horizontal control point. If you try to do that with say 4 minute averages over several hours or days you will see that although your GPS receiver may report that it is good to 5 feet or so, you will find that your positions actually vary by up to several meters even with WAAS on. In the woods it can be 3 or 4 times worse. WAAS cannot model local conditions and errors which affect your receiver.

 

= jlw

I am not so much trying to check my GPSr as much as I am comparing the results with and without WAAS. When WAAS was broken I wondered if I has lost anything as far as accuracy goes. Now that it is working again I thought I would try to figure out what if any benefit WAAS has when Geocaching. My first test showed WAAS to be less accurate.

Share this post


Link to post

Well I gave the test another try. This time I simply switched the WAAS on and off with the secret menu. The short of it is that there was no meaningful difference.

Share this post


Link to post

HH2 at best is likely really +/- 50 foot diameter, DATASHEET maybe 400 ft diameter. Get close, get out the tape, look for subtle clues such as old fence line berms with no barbed wire, newer road or RR alignments and have fun being out there - or invest in survey grade GPS. MEL

Share this post


Link to post

Usually better than 50 feet, but the advice is good - use the To Reach information.

 

I conducted an experiment recently with averaging to find the ultimate accuracy I could achieve. I set my Garmin 76s to User UTM with a scale factor of 3.28083 to get a readout in feet so I could see past the display rounding of lat-lon formats. The reference meridian was near my location and the false northing and easting were set to something that gets display values that fit in 9 digits.

 

I averaged a waypoint with WAAS on for typically over an hour, getting indicated accuracy values of 1.3 to 2.4 feet on the unit. I recorded the position in feet. I ran an averaged waypoint 12 times at various times on several days and plotted the results in a spreadsheet. Sorry that I don't know how to convert it to a jpg to display the graph directly.

 

Individual points were spread over 6 feet east and west by 12 feet north and south with a standard deviations 2.0 x 3.8 feet (radius 4.3 feet). For 95% confidence, double those values. This was for a less than ideal site, in my driveway 50 feet from the house with aluminum siding and with a leafless tree looming in part of the sky. I used that point because I am also using it as part of a triangulation network and it was easy to go check on it every hour.

 

I explain the discrepancy of the standard deviation versus the displayed Indicated Accuracy (unknown if intended to be sigma or 95% conf) by assuming the unit makes no allowance for multipath reflections, but only considers the noise in the signal and the display roundoff.

 

As you can see from this data, multipath or other ionospheric effects don't average out in an hour.

 

I know the unit has internal computational errors of 2 to 4 feet because when I ask it the distance between combinations of points on a line the sums and differences disagree by that amount. That says that getting below the 1 foot level in display precision would gain nothing.

 

To convert from the feet values, I enter four round-number Lat-Lon waypoints in roughly cardinal directions from the unknown points and assume the GPS unit represents them within its internal computational precision in any format. I average the displayed feet coordinates for those four waypoints and equate those values in feet to the center of the values in Lat-Lon. That gets me a little averaging of computational error. I figure the offset of the unknown point (average of many sessions) from the center of the four points.

 

The averaged position would be in WGS84 (I think G1150). The average shift around here to NAD83(1996) is 3.7 feet (NAD values smaller west and north) according to HTDP. Individual points in the horizontal control network may differ from the average value given by HTDP.

 

The result doesn't fit well with my triangulation, but that's another saga.

 

If anyone is interested, I'll try to clean up my working paper on this subject and make it available. It discusses all the tricks I have tried in this quest. The one described above requires the least work in the field, but it took me a long time to discover it.

Share this post


Link to post

Maybe I am just lucky but I sure get excellent readings within 2 or less feet usually.

 

I have often wondered about the GPS timing.

They are all on the same time aren't they?

 

GPS TIME TRANSFER

 

GPS is at the present time the most competent system for time transfer , the distribution of Precise Time and Time Interval (PTTI).

The system uses time of arrival (TOA) measurements for the determination of user position.

A precisely timed clock is not essential for the user because time is obtained in addition to position by the measurement of TOA of FOUR satellites simultaneously in view.

 

If altitude is known (i.e. for a surface user), then THREE satellites are sufficient.

(Everyone always asks me why I like to have the closest altitude along with the coordinates,maybe this is the real answer).

If time is being kept by a stable clock (say, since the last complete coverage), then TWO satellites in view are sufficient for a fix at known altitude. If the user is, in addition, stationary or has a known speed then, in principle, the position can be obtained by the observation of a complete pass of a SINGLE satellite.

This could be called the "transit" mode, because the old TRANSIT system uses this method. In the case of GPS, however, the apparent motion of the satellite is much slower, requiring much more stability of the user clock.

 

Now if you read more into this you will find some very interesting facts.

USNO NAVSTAR

 

I guess it all depends on how satified you are with the accuracy of your handheld.

I am keeping mine and am very satified with the results I get and have been getting.

 

If I was to make a career out of it I would invest in one that has the L1 and L2.

Then there is that other qualification as well.

Share this post


Link to post

I'd be interested to know what model you have, and the actual readings for several different times/days at the same point.

Share this post


Link to post

1995-6

Well way back when I started learning and I had the only GPS in this area I use to keep track and do readings at precisely noon each day.

I kept logs and would sit and calculate for hours trying to figure out all the answers.

This was when SA was still turned on and I was learning with a GPS that only had 2 decimal places,so I used angles.

This is also when I came up with my GEOID like ideas.

 

I used Stations on the ground and Historic Monuments to calculate a Triangle with a Base Line of 3 Miles using Triangulation Stations for control.

I still have all that mapped out on some charts and break downs into the second of time both North South and East and West.

 

2008-9

Now I wish I would have kept all that data I looked up and have and would have to go through to recompile the massive amount of time I spent doing all kinds of experiments and I do not have the time to sit and get it all uploaded to the forums.

 

I am basing all my logic off of real time experience,study and trying to keep fairly accurate details but there became a place for me where it became a mute point because I do not have any type of Official authority.

 

I have several units but use the Garmin Rino 120 the most with WAAS on now.

And with a great program that will pull more decimal places than the unit will display.

I also and you can use your Laptop at some stations now days,in fact I have driven right up to several using that device.

 

Here it is at a benchmark in my front yard, one of the many 2nd and 3rd Order Control I need to add to Waymarking.

862bd446-e7fa-4212-9666-e5803674364e.jpg

 

WM44N 5 HBS 1973

 

I could probably go out anytime and get that average at this Benchmark.

I could set up my laptop post process the ephemeris and what is all that other stuff.

 

The EDM Base Line Tests I have posted somewhere are not as much data as I was going to get but when it told me at 150 meters I was 150 meters from Ground Zero and to the 400 and end I think it was 1380 and 1240 or on that order I said for me that was close enough.

 

Now I still try to time things and probably do not take the time I should to write down everything but I feel that if I found what I was looking for putting a numerical value to the imf point is irrelevant.

 

It is like me trying to convince some one else.Only one I have to really convince is me and I am.

 

I have to remember also and for others I am just a Volunteer.

Share this post


Link to post

I am using two Magellan Meridian Gold units. I was getting around 6 ft. from ground zero at best, while standing on top of the Benchmark that was used for my waypoint. I am only comparing WAAS for use in Geocaching. Under normal Geocaching conditions I only stand near ground zero for a fairly short period of time. Which way is more accurate under normal Geocaching use is what I am curious about.

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  
Followers 2

×