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Discussion Starter #1
Lat/Long differences between Google Earth and my GPS

I used my GPS to get a location fix to make sure I was looking at the right area on Google Earth. The two were different by at least 200-300 yards. Is this normal? I've noticed tha same between my GPS and DeLorme software.
 

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Re: Lat/Long differences between Google Earth and my GPS

Dave

what model GPS? How old is it?

There may be a datum issue going on. WGS-84 and its many refinements, or NAD83 and its many refinements.

However, it shouldn't be 200 yards.

As far as DeLorme, and Google Earth, I've never checked their accuracy compared to survey grade data. I might try that just to check.

jeff
 

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Re: Lat/Long differences between Google Earth and my GPS

Also,
make sure you have the same units

decimal degrees
versus
degree minute seconds
versus
degree decimal minutes.
 

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Re: Lat/Long differences between Google Earth and my GPS

Dave, I am glad that you picked up on the difference. I find Google Earth to be three or four hundred feet off. I was putting some landmarks into a CAD system, and then taking the Lat/Long and viewing it in Google Earth. Google Earth is close but a ballpark away.

Outfit called NorthTree Fire has done a lot of wildland fire mapping and has noted the accuracy issue. I did not look to see if they have resolved the issue with Google but here is an interesting link from a tactical standpoint. http://www.northtreefire.com/gis/virtual.php

When I transfer Tracks to Google Earth I find the results satisfying.

I believe the allowable error on a USGS Topo is twenty feet.

As an example using USGS State Series Topo I determined the Lat/Long of an isolated spring box. Not far from the box is a nice little flat that people camp in. On occasions emergency services have to respond to that location. The information entered in the CAD was field checked later by a field unit.

One problem we had with DeLorme was that it showed roads where roads do not existed. It showed a road on the wall of a steep canyon where it was not practical to build a road. But DeLorme has been helpful in other situations. A few years ago I used DeLorme on a problem and the results were very satisfying. I would consider the results mixed but in favor of DeLorme. I have not used DeLorme much of late.

I do not have the most current version of DeLorme but in the past maps from the USGS State Topo Series have taken care of my needs. DeLorme, Garmin, MapTech scan USGS topo data and create their software product. Most of USGS data is over twenty years old, and with the current budget problems in the government they will not be updated for a long time.
 

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Re: Lat/Long differences between Google Earth and my GPS

I have a Garmin 60c and I've had it two years or so. Thanks for the replies. I'll check on the units. That's a good point.
 

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Re: Lat/Long differences between Google Earth and my GPS

ncsurveyor, you are right on. I changed the units to (hddd 'deg' mm 'min' ss.s 'sec' ) and it fixed it. Note: on my GPS there are the degrees, minutes, and seconds symbols on the selection.
 

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Re: Lat/Long differences between Google Earth and my GPS

Dave said:
ncsurveyor, you are right on. I changed the units to (hddd 'deg' mm 'min' ss.s 'sec' ) and it fixed it. Note: on my GPS there are the degrees, minutes, and seconds symbolys on the selection.
I once processed a survey for some guys, and we had a mild units issue.

I was only off by 257 miles, and change.

Glad to help.

jeff
 

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Re: Lat/Long differences between Google Earth and my GPS

ncsurveyor said:
Dave said:
ncsurveyor, you are right on. I changed the units to (hddd 'deg' mm 'min' ss.s 'sec' ) and it fixed it. Note: on my GPS there are the degrees, minutes, and seconds symbolys on the selection.
I once processed a survey for some guys, and we had a mild units issue.

I was only off by 257 miles, and change.
I had this happen once and it turned out to be a case of one units corrdinance being in Decimal degrees while mine was set for decimal minuets (or vice versa)
I forgot how to do the conversion but maybe Siskiyou could explain it if deemed nessary.

I am basically using an older Garmin Gps 12 and a 1996 copy of the Delorme Street atlas which covers rural areas. (I know, gotta get an update) I also use a navigational program meant for pilots. The thing is that these two programs and my GPS seem to agree to the penny on a good day, which most of them are.
 

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Re: Lat/Long differences between Google Earth and my GPS

Whoop's, I should have been paying more attention to the above posting.

ncsurveyor, I think that you straightened this out for me on the coordinates for the first Michigan shoot that happened near Grayling Michigan?
This happened at least three years ago and the shoot has evolved into the Mark Severans (sic) memorial shoot.
 

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Re: Lat/Long differences between Google Earth and my GPS

glanceblamm said:
Whoop's, I should have been paying more attention to the above posting.

ncsurveyor, I think that you straightened this out for me on the coordinates for the first Michigan shoot that happened near Grayling Michigan?
This happened at least three years ago and the shoot has evolved into the Mark Severans (sic) memorial shoot.
If it was me, it wasn't here. I've only been on GB for a half-year or so. But the scenario does sound familiar, because decimal degrees is fairly odd these days.

That being said, I did live in Michigan, but that was years ago. Before I became a surveyor.
 

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Re: Lat/Long differences between Google Earth and my GPS

When using Google Earth along side your Garmin or Magellan gps unit they must be set on the same unit of measurement. In Google Earth select tools, options, show Lat/Long. Select the unit of measurement that you are using on your gps.

If you are a Garmin gps user select Main Menu, Setup, units, and select from the drop down the appropriate measurement.

While some use UTM others use other measurements. Most of the surveys in my part of the country were done in hddd°mm.mmm’ format. And when finding “K” tags out in the woods I find this format in use. Federal agencies also use this format in fire reports. It is modified for aircraft dispatching because older aircraft guidance units will not except the last three digits. But to confuse things the same agency uses hddd°mm’ss.s when documenting law enforcement incidents. The nice thing about the CAD system I am familiar with is that the dispatcher enters the location in the format given and then system generates the lat/long is several formats allowing compatibility with a number of systems.
If I create a lat/long in by gps as N41°43.894 W122°38.139 and I need to covert it to UTM UPS in the field I can easily go to Main Menu, Setup, Units, and scroll down the options until I find UTM UPS. UTM UPS is commonly referred to as UTM. Your gps does the conversion for you automatically. It is not a math problem for the user. The same location becomes 10T 05303000 4620037 . Looking at a number of Forest Service and BLM maps I have the units of measurement used are hddd mm.mmm' , UTM, and Township, Range, Section, and Meridian. For an old duffer like myself

http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system

Dave in WV sent me some Google Images that he created before and after changing units. From the results of his imaging, and a little I did this morning it appears that now having both Google and your gps set on the same units gets the same result. I would not be surprised that Google reacted to the concerns that North Tree had regarding disaster mapping accuracy.

Google Earth is a neat tool. A while back I was given the location of a smoke from a citizen. The citizen was looking at the mountains about twenty miles from his location. The citizen provided a compass bearing and an estimated location. When I put the estimated location on a Google Earth Image and rotated it I immediately realized that the location was not correct. Because it was a thousand feet in elevation behind a peak from the reporting party. But using Map Source I created a route using the bearing, and viewed it in Google Earth. This displayed the search path for the smoke.

Units of measurement on a map can cause a lot of problems. As an example a lady calls an emergency dispatch center and says she has a problem. She tells the dispatcher that she is located at A-12.

The dispatcher quickly types A-12 in the computer. And does not get a result.

The dispatcher ask for additional information.

The woman becomes angry and says she is at #@%& A-12 on the map she bought from the service station.

Unfortunately A-12 can be a different location depending on the map being used.

In one County A-12 is a road number, in another it is meaningless.

The bottom line is that we need to be consistent when using units of measurement. Just remember that there are 66 feet to a chain, and 80 chains to mile.

Glanceblamm if I failed to answer your question please let me know.

;D
 

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Re: Lat/Long differences between Google Earth and my GPS

Pole: You have me going on this one. It could be the North Pole, South Pole, the Magnetic North Pole, Magnetic South Pole, Swedish Pole (Survey), or a 12-foot Composlite Prism Pole. Then there could be the Pole Man or in the politically correct world Pole Person.

Help me on this, is there a standard measurement for a survey pole. I suspect the measurements of the pole are in parts of and inch or defined in metric measurements.

http://celebrating200years.noaa.gov/survey_towers/swedish_pole.html

http://en.wikipedia.org/wiki/Earth's_magnetic_field

A point of interest is that if you go to the Main Menu Page, select Setup, and Heading. The Heading page gives you a number of options, starting at the top is Display. Display gives you the option of displaying your heading in Cardinal Letters (NEWS), Degrees, or Mils.

In this example the units of measurement in his gps should match the unit of measurement on his paper map. Otherwise it does not make a big difference.

Your next option is North Reference. There are four options; the two I have worked with are North, and Magnetic. The factory default is North.

And there is the Magnetic Variation screen. It will display the degrees to Magnetic North in degrees E or W. This display is important because you can adjust your compass declination with this information. Normally at the bottom of a USGS Topo map you will find the UTM Grid and the Magnetic North Declination at the center of the sheet.

Does this information mean a great deal to the to the average gps user, I think not. But for the hunter with a backpack on his back and he is looking at a distant rock point. He goes to the FIND page, selects the Geographic Points Page, and his gps starts searching for different points. A screen pops up and gives him a number of locations. The direction and mileage to Buck Mountain appears correct, he selects the Map option and Buck Mountain again appears to be correct. He hits the Quit button what takes him back to the earlier screen, and he has two more options. Save or Go To. At this point I would select the Save option, it saves Buck Mt as a waypoint. And it has brought up the Waypoint screen with the Go To option; I would then select the Go To option. In this case the gps tells the hunter that Buck Mt is six miles away. Those are air miles or map miles, not boot miles in the mountains. Just to be sure the hunter pulls out his magnetic compass and shoots a bearing to Buck Mt. The hunter also creates a waypoint for his vehicle so he can find it in the dark. And records the back reading on his compass.

The hunter takes a buck on his way to Buck Mountain, cuts the buck in half and hangs the other half. He creates a waypoint so he can find it on a return trip.



* Must have Topo software or other software loaded for the points of interest function to work.

I recommend that users of Google Earth Plus go to Google Earth and transfer the Tracks and Waypoints generated from their hunts. I printed out Google Earth Images and carry the approiate one in my daypack.
 

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Re: Lat/Long differences between Google Earth and my GPS

4 poles to a chain.

1 pole = 16.5 feet

depending on your part of the country, poles are called rods and are the same
 

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Re: Lat/Long differences between Google Earth and my GPS

My Dad was raised in Michigan and used the terms Rods and chains, but I cannot recall ever hearing the term Pole in relationship to land measurements. Thank-you for the vocabulary word.
 

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Re: Lat/Long differences between Google Earth and my GPS

Siskiyou said:
http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system


Glanceblamm if I failed to answer your question please let me know.

;D
Siskiyou
Ya did very well. I followed your instructions and found that mine was setup as hddd mm.mmm (I dont remember how to make the degree symbol)

I could not find the UTM UPS though...
I found Map datum (which reads WGS 84)
I found Cdi (which reads 20.25)
And Units (which say's statute)

I think that my Garmin GPS 12 is at least 7 years old. The setup menu contains...
System
Navigation
Alarms
Interface
Language
I dont know if this description helps you any or perhaps can tell you if the UTM UPS is something that mine might not have?

I do know how to operate it very well and it has been a great source of function and entertainment.
 

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Re: Lat/Long differences between Google Earth and my GPS

I have no experience with the GPS-12. I took a look the manual for the GPS-12 and it appears that Garmin may have dropped or changed some terminology in later models. The CDI scale is used on the Highway Page. I must admit that while I have played with the Highway Page, I have not used it. A friend of mine who sails the Sea of Cortez uses it a lot.

CDI stands for Course Deviation Indicator. Page 34 of the GPS-12 manual explains how this works.

I have paid some attention to CDI when using the Garmin Legend, 76C and 76Cx. If you are using the Course Pointer on the Compass page you will see a Pointer, and a Compass Ring, which work independently of each other. If you are navigating to a waypoint you will also see a broken dash line on the face of the compass. This will indicate the direction you need to be traveling to be on course.

The best environment for using the highway page and taking advantage of CDI is open water. Navigating the Great Lakes would be a good location.

Page 44 tells me that UTM UPS is an option on your unit and how to change it.

The default map datum is WGS 84. Using the incorrect datum can affect the accuracy of you data if your paper map datum is different then your gps datum. NAD27 is commonly used on many USGS topo maps.

You can find the manual for the GPS-12 at Garmin.com under support.

The GPS-12 was an early 12-channel gps unit. It was widely used by S&R groups, law enforcement, and outdoors folks.
 

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Re: Lat/Long differences between Google Earth and my GPS

Thanks!
It has been lots of fun as said. I did know what the CDI was for. Have seen it work on the highway. This unit does have a highway on it but it does not know which one!. It is simply a matter of how many markers that one has on a route and how big of a curve there is in the road ahead. During testing, the overpasses were great places to place a mark that was pre-programmed using the Delorme, They are right on the money for the most part as is a Delorme reading for an old cemetary or a way out bridge.
For highway usage it is great for getting the right exit, specially when those tall tractor trailors are blocking the overhead signs!!

I have also had this on aircraft. Our little turbo-prop was clipping right along as it was doing 288mph @ 7,000ft. The landing was a procedure approach. If you dont know what this is, the aircraft overflys the runway from the opposite direction and proceeds six or seven miles to the outer marker. At that point, a 45degree turn is made for one minuet then a 180degree turn is made and the pilot is watching for the needle to sweep across the vor so he can turn on final. My Gps 12 drew a beautiful picture of this. The pilot was taken by surprise though when we were on the ground and I ask why we had overflown the outer marker by seven miles! Traffic issues. was his reply.

I also had it on a commercial flight. 520mph @ 33,000ft is kind of sobering to think about if something should go wrong!
Highlights of this trip were watching how the pilots were doing. For the most part they were right on the line, sometimes a degree to the right or left but the plane was flying beautifully according to the route on the gps.
I was able to see town lights way down there on this night flight and would mark them. I was able to find the exact course when I transferred this to the Delorme at home.

Special Note: In Today's Air Industry They will probably make you SHUT OFF ALL ELECTRONIC DEVICES when the seatbelt lights come on for the landing. This is because of possible interference of the so called fly by wire controls.

I get the most usage out of my gps on foot or in an auto. This can range from city to woods as it is quite versitile..In the woods, I will usually make marks every 1/2-3/4 mile and shoot compass courses in between. The thing works just as well in simulator mode as in real mode providing that you are at a known marker which is easy enough to identify. One thing is for sure, when this one quits, I will purchase another.
 

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Re: Lat/Long differences between Google Earth and my GPS

A few years back I carried my Garmin Legend on Southwest. Security checked, turned it on, and I showed them the batteries and they let me go. On board I had a window seat, and was playing with it in plainview because I felt the I would be questioned about it. It did not take long and a polite steward was asking what I had and I explained a gps, and showed it to him. No problem, no guarantee that it will always go that way on another flight.

I carried a gps with me on AMTRAK this summer. I made a comment the train was going 82 miles per hour. The conductor told me I was incorrect, we were doing 78 mph. (The speed limit on the track is 78 MPH for safety reasons.) I thought it was strange the gps has always given me the correct speed in the car. I think he gave me the legal response, not the correct response.

At times I take the opportunity to expound on different terms or subjects brought up in a post related to gps in case the information will help other users.

I have you found the UTM option on your GPS-12?
 

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Discussion Starter #20
Re: Lat/Long differences between Google Earth and my GPS

Your speedometer reads different than the locomotive's. :eek: ;) ;D
 
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