Google Earth UTM question

[gldnbrew]

I am using UTM for archaeology finds (no I am not one). When I transfer (from a Garmin) the data to Google Earth the entire location is there(ex:17T 450105.93) However when I open up the properties & change the push pin color or rename it, it changes the reading by changing the numbers following the decimal point to .00 (ex:17T 450105.00). Did not do this before, the older data is OK.This is a recent development and I would like to be able to change the push pin color and rename it without losing the numbers after the decimal point.

Thank you,

Paul

P.S. I tried to manually to put the correct numbers in, but it does the same thing, rounding to the nearest whole number.

 

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[Clay Diggins]

The UTM (Universal Transverse Mercator) location is expressed in meters distance from the reference datum. You are trying to express fractions of a meter on a mapping system that has an accuracy of less than 1/4 mile. The rounding is normal for most UTM mapping and expressing a location in sub meter accuracy is impossible with online mapping systems.

If you want more accuracy you could move to a projection in feet or move to a mapping system that has sub meter accuracy. Even then Google Earth is not equipped to do what you want. Even the meter accuracy is extremely suspect and should not be relied on.

What type of application are you using that requires sub meter accuracy? Your Garmin output is repeatable to 30 foot on a good day. Nine foot is the highest resolution possible with a modern Garmin and that would involve a good lock on several satellites along with a lock on two WAAS repeaters while in a southern setting with no tree cover on a clear dry day. The Saint Lawrence Seaway will never meet several of the requirements for GPS accuracy of that level. Nine foot is not sub meter and not repeatable on a consistent basis with commercial grade GPS even in the best of circumstances.

If you want to use Google Earth for your mapping you will need to understand that they simulate meter accuracy and get used to the idea that it will commonly vary depending on more factors than Google is willing to share with it's users.

 

[gldnbrew]

Thanks for the response. I am OK with with the way my Garmin plots my finds in Google Earth, but I am working with an archaeologist and I was just trying to preserve the sub meter data for him. He has a more sophisticated mapping system. My question is why does my older data (last year) retains the sub meter data after a naming change, but the new data will not keep the sub meter data. From the standpoint of my research, sub meter does not effect me. I am looking for the overall picture, which does seem to be relatively accurate in Google Earth, at least all that I need it to do. Note; I mark all my finds at +/- 9 feet so at least they are consistent as I can make them.

Paul

 

[AUVnav]

Have you tried just converting the data to LAT/LONG and using that? This is very, very accurate. GE uses WGS84, not UTM, so it is far better that you convert to WGS84 to avaoid the rounding errors.

You can also directly access the .kml file. Make a copy of it before you make any changes. You can save what you have as a .kmz file, then open it with a kml editor and make the changes , additions that you want.

the kml file is located on your computer at C:\users\username\appData\LocalLow\Google\GoogleEarth\myplaces.kml

 

[Clay Diggins]

Google Earth uses a Plate Carree projection. It is essentially a spherical projection.

WGS84 is not a projection it is a datum reference. It describes a set of points on a non round earth. WGS84 can be used with any projection with equal accuracy. Google Earth is projected to EPSG:4326. To convert to meters or back into degrees in Google Earth is trivial.

function latlng2xy($lat,$lng) { $x = $lng; $y = rad2deg(asinh(tan(deg2rad($lat)))); return Array($x,$y); }

function xy2latlng($x,$y) { $lat = rad2deg(atan(sinh(deg2rad($y)))); $lng = $x; return Array($lat,$lng); }

A rounding error in meters is a maximum of 18 inches. Google Earth does not support repeatable resolutions better than 1320 feet so the 18 inches is well within any margin of error. You can't improve the resolution of Google Earth but you can avoid introducing errors by turning off the "terrain" feature. The 3D features really mess up any accuracy Google Earth had in the first place.

Please read your Google Earth license to find what guarantees Google gives about Google Earth accuracy.

Google makes no claims as to the accuracy of the coordinates in Google Earth. These are provided for entertainment only and should not be used for any navigational or other purpose requiring any accuracy whatsoever.

I think the original post was addressing the loss of measurements resolutions below one meter resolution. This accuracy would not change whether it was meters, or lat/lon. The resolution will remain the same either way. Since the GPS system they are using has a maximum resolution of +/- 9 foot (within 18 foot or 6 meters) and a standard resolution of +/- 30 foot (60 foot or 20 meters) I'm unclear why either a rounding error of 1/2 meter or any error less that the resolution of the original input could possibly matter.

The ultimate user will be no better located with sub 1 meter resolution that with 3 meter resolution. Either one is just as an inaccurate representation of the original data as the other.

If you feel you must save the original data in it's original resolution just download the GPX file twice to two different locations on your hard drive. If you need to convert the GPX file to kml or kmz or some other format there are much better free tools that Google Earth to make that conversion.

I hope that helps.

 

[AUVnav]

Sorry, but I disagree. WGS84 is a spheroidal project and the EPSG:4326 is just the latest version.

Both the GPS systems and GE use WGS84 for horizontal and vertical datum. Why set the GPS to UTM, only to have to convert?
GE will use coordinates to 2 decimal places in seconds, this is relative. If you put it in at that accuracy, it will report that accuracy, and will find it again.

The original poster just wants to map the horizontal location, and with one sig digit in seconds, that is 3/2.4 meter accuracy (lat/long)

BUT, in placing the location in with 2 sig digits, it will be relatively accurate to about 1 foot. This way, any locations that are recorded by the GPS and placed in GE, will be relatively accurate to each other by a foot.

 

[Clay Diggins]

That's a common misunderstanding AUVnav.

The datum (WGS84 in this situation) can be applied to any projection (EPSG:4326 for Google Earth). The two are different aspects of presenting mapped representations.

I can apply the WGS84 datum to the Google maps non-standard 900913 UTM projection and the same points from the datum will be in the same spots on the UTM projection map.

HERE is a link to a fairly clear explanation of the differences between datum and projections.

 

[AUVnav]

In regards to GE, they use WGS84. Note: The latest revision is WGS 84 (aka WGS 1984, EPSG:4326) World Geodetic System - Wikipedia, the free encyclopedia

Okay, there are many ways to use the datum. Getting back to the op.

The GPS unit should be set to WGS 84, not UTM, correct? There is no need to convert.

The way to change the colors of the pushpin, and name can be done with a kml editor. You could even change the symbol from a pushpin to whatever you want in a kml editor.

 

[Clay Diggins]

The WGS4 datum and the EPSG:4326 projection when combined form the CRS (Coordinate Reference System) that is used for Google Earth (and elsewhere).

The WGS84 datum is not tied to the EPSG:4326 projection except when they are used together to form a particular Coordinate Reference System (CRS). A CRS is commonly misunderstood to be a projection but it is not.

Here is some more reading material to help clarify this common misunderstanding:

Coordinate Systems and Map Projections

Some people casually refer to any coordinate system as a "projection", but this is not strictly true. "Geographic" coordinates, latitude and longitude, are in fact not considered "projected."

On Map Projections and Geodetic Reference Systems

A map projection needs information about a reference surface.
A geodetic datum fixes the reference surface in space (superior coordinate reference system).
Changing map projection between countries normally need a geodetic datum transformation.

The accuracy of locational data on a projected map depends on the datum and not on the projection or the units used to express the location. The equivalent of one meter distance change at the original posters latitude is lat/lon expressed to the fifth decimal place. Neither is more accurate than the other.

The problem with lat/lon measurement is that angular measurement is not fixed. The same distance on the map is a different numbers of feet or meters depending on the orientation of the angle (Degrees Minutes Seconds). Lat/Lon is not a unit of linear measurement but UTM is. UTM location information is expressed as the number of meters from the zone reference. With UTM 10 meters in any direction from a single point on the map is 10 meters in real life unlike Lat/Lon.

That is why the original poster's Archaeologist friend is working in UTM. Since Lat/Lon is incapable of expressing linear measurement even the accuracy and resolution of Lat/Lon projections is expressed as meters.

As I wrote, it is trivial to convert between the projections. No accuracy is lost in the conversion and the time it takes to do the conversion, on a computer capable of running Google Earth, is not within the bounds of human time perception. There is no slow down no matter which system is returned as the result. That's why Google Earth offers UTM coordinates as an option.

 

[AUVnav]

Sorry, but again, I must disagree. UTM is based on a baseline offset, where WGS is absolute.

Every measurement, no matter what the datum, is not based on a straight 2D line, but based on the the reference to the datum. Straight line to straight line is easy, based on the approximation of the surface. Add a curve, and all bets are off.

I do not agree on the accuracy globally that you state. Once you take the first measurement, then the proceeding measurements are relative to the first, not globally. This is a distinct difference.

 

[Clay Diggins]

You might reasonably disagree but you are disagreeing with the standards organization itself.

If what you supposed were true the following would not be possible.

EPSG:32610

EPSG:32611

and about 120+ other WGS 84 datum / UTM projection pairs.

It's done all the time and there is no degradation of the WGS 84 datum accuracy.

That's why it is so important to understand that WGS 84 is a datum - UTM is a projection. Two very different things.

Notice what the projection scope is for this and all WGS 84/UTM projections:

Scope: Large and medium scale topographic mapping and engineering survey.

Specifically designed for precision mapping.

 

[AUVnav]

You must get lost quite often.

There is no need to go with the UTM projection. Each UTM zone has a baseline, the further you get away from the baseline, the more inaccurate the UTM reference will be.

Since WGS84 is absolute, you will get the exact point you are sitting other, rather than a projection from the gridline.

Since the WGS84 ellipsoid is what UTM is based, why bother?

With the UTM banding of the Earth, the zones get more distorted the further North/South you go...

This was the system before GPS was invented, so why not evolve?

I see no reason to overly complicate the issue and decrease the accuracy by using UTM

 

[Clay Diggins]

You must get lost quite often.

Although my facts may have disputed your theory AUVnav there is really no cause to question my ability. Making personal comments when you have no response to the facts is rather unproductive isn't it?

But to answer your query - no I do not get lost - ever. I'm a cartographer and I make maps that vary in accuracy from three meters down to sub-centimeter accuracy. Not your average road maps. I make these maps in several datum and many projections including custom projections designed by myself just for a projects particular needs. I know my way around both projections and datum better than most people know their way around their house.

It's obvious that you are not understanding that difference. That's OK - unless you are a cartographer and people rely on your maps. Let's just agree that you disagree with whatever I may have written and move on to:

Happy Thanksgiving to you and yours AUVnav.
May you relax and enjoy this holiday as your best ever!

 

[gldnbrew]

Amazinig ! All this out of, what I thought was an easy question. " I would like to be able to change the push pin color and rename it without losing the numbers after the decimal point." Like I was able to do last year.

I can see cartography is not in my future, my datum's are awry and my math skills are sadly lacking. I am having trouble just reading this;

function latlng2xy($lat,$lng) { $x = $lng; $y = rad2deg(asinh(tan(deg2rad($lat)))); return Array($x,$y); }

function xy2latlng($x,$y) { $lat = rad2deg(atan(sinh(deg2rad($y)))); $lng = $x; return Array($lat,$lng); }

But I did stay in a Holiday Inn Express last night.
By the way, I am taking on the challenge of mapping the Prussian incursion of 1807. Can I count you two

Paul

P.S. If you have never heard of Prussian incursion of 1807. Check it out

[/video]

 

[Clay Diggins]

Paul I could show you how to change the kml file in your text editor to change the pushpin color without loosing those extra decimal places but I'm guessing that would be more confusing than the math.

You really can't expect the script kids over at Google to keep some feature because it works and people like it. For them it's all about "change is good". Next they will only support matching colors for the pushpins.

As far as the Prussian Incursion map ... someone already beat you to it.

IEG-MAPS

Ain't the Internet wonderful!

 

[gldnbrew]

As far as the Prussian Incursion map ... someone already beat you to it.


DAMN ! Oh well at least the cargo survived.