HELP! Need to import accurate Coords in to Google Earth? how

[3dmax]

Hi All

great little forum here! can anybody help.... must say i'm a real Newbee to GPS stuff but it seems like a lot of fun

I have a Garmin Vista .... I take some waypoints in South island download to a *.GPX file or excel

but tried importing the points into Google Earth? and all points seem about 50m out by SE direction?

I have been told ? that its because Google Earth sattilite pics works on WGS84 and not on the kiwi way???

How do i convert coords to WGS84 to import into google earth to make sence? or is there something else amiss?

How accurate do you guys think the Garmin Vista is ?? it never gets less than 5m Accuracy it states but how real is that and any tips to get Max Accuracy?

any Help much appriciated

3dmax

[BaldEd]

Hi All

I have a Garmin Vista .... I take some waypoints in South island download to a *.GPX file or excel

but tried importing the points into Google Earth? and all points seem about 50m out by SE direction?

I have been told ? that its because Google Earth sattilite pics works on WGS84 and not on the kiwi way???

How do i convert coords to WGS84 to import into google earth to make sence? or is there something else amiss?

How accurate do you guys think the Garmin Vista is ?? it never gets less than 5m Accuracy it states but how real is that and any tips to get Max Accuracy?

any Help much appriciated

3dmax

Hi 3dmax,
The most commonly used gps datum is WSG84 and you will need to change your vista to that. It is quite easily done. Although I don't have a Vista it is probably something like: Goto SETUP MENU > NAV SETUP. On this page scroll down to MAP DATUM and highlight whatever datum is displayed there then using the up/down buttons scroll through the list until WSG84 is displayed. Press ENTER and youve done it. If you have any difficulty then go read the Vista's manual, it will be all explained in there.

Geocaching, aircraft navigation etc all use WSG84. All the other datums are used mainly by paper maps/charts. If you want your gps to align with a particular map/chart then change your gps to the map/chart datum - this is usually specified on one the borders of the map/chart.
Cheers,
Eddie

[BrentC]

and all points seem about 50m out by SE direction?

What are the co-ords

Probably be that Google Earth pics are off by 50m

[kiwilegend]

How accurate do you guys think the Garmin Vista is ?? it never gets less than 5m Accuracy it states but how real is that and any tips to get Max Accuracy?

As accurate as any other if it has a good view of the sky. It hasn't got a great antenna, so if you are in a restricted sky-view area, you won't get as good a value as other recievers with better antennas.
Although it says 5m it is probably really 2/3 of that, based on typical accuracies you get when geocaching.
There are no real tips - other than getting a clear view of a lot of sky.
All Garmins also appear do some 'averaging' to remove noise. So sometimes there can be an accumulated error. I'd suggest that if you want to mark an accurate coordinate, you do a bit of a 'cross' pattern movement of a few metres before marking the point. And check it a bit later too, by doing a 'goto'.

[3dmax]

wow thanks Guys for the quick responce

@kiwilegend - thanks for the advice I try a bit of this to test it? i once saw a website or programme that gave you the best time of day to take a reading of a Coord to get the best accurate reading from a satti overhead??

@BrentC - i will dig out the Coord out and post them I have head that once you have a *.gpx a programme will adjust all the Coords to one way or another then create a new *.GPX that will tie up with Google Earth pictures? a germany proggie? nh-toptrans???

@BaldEd - thanks
So if I upload the original waypoints into the GPS and adjust it to WSG84 the download the *.GPX file this should be correct ? is that what you are say BaldEd?? ...or are you saying i have to take the readings again with the GPS in WSG84 mode then download the new *.gpx file?? ( this is prob not possible)

thanks

3dmax

[rediguana]

A couple of points...

1. When downloading co-ordinates from a GPS (consumer at least, not sure about commercial survey GPS) - they are always downloaded as WGS84. Selecting an alternate representation such as NZMG only affects how it is displayed on the GPS itself. If you want them converted to something other than WGS84 when downloaded, you'll have us special software like DNRGarmin to convert them to NZMG. If it was a NZMG error, you'd be out by 200-300m.

2. You may be experiencing the 50m from a multitude of errors. I've noted that there is a 10-20m error in the new Google Earth imagery - it needs to be shifted about this far SSE-SE to be correct (noted from multiple tracks biking, on different days, different GPS (including friends 60/sirf) and on good clear ground) - hence the tracks are consistently out (I'll post some images at some point to show what I mean). You may also have had an error from poor signal - the combination of the two may have produced this larger error. It is also possible that the georeferencing error of GE imagery varies over the country and may be 50m where you live. I'd be interested to hear from others what sort of errors they are getting when overlaying GPX tracks in GE.

Cheers Gav

[BaldEd]

I just checked where the latest GE image displays my Silica City cache. It pinpoints the cache approx 4 to 5m NE of the actual physical location. Certainly that error is within gps tolerance but cachers had still better read the hint anyway.

[BaldEd]

@BaldEd - thanks
So if I upload the original waypoints into the GPS and adjust it to WSG84 the download the *.GPX file this should be correct ? is that what you are say BaldEd?? ...or are you saying i have to take the readings again with the GPS in WSG84 mode then download the new *.gpx file?? ( this is prob not possible)

I would suggest that before you upload the gpx file to your gps that you set the gps datum to match the datum that is in the gpx file i.e. the datum used when the waypoints were recorded. After you have loaded the gpx file then just change the gps datum to the datum you require and all the waypoints will be changed to reflect the new datum automatically.

[3dmax]

I would suggest that before you upload the gpx file to your gps that you set the gps datum to match the datum that is in the gpx file i.e. the datum used when the waypoints were recorded. After you have loaded the gpx file then just change the gps datum to the datum you require and all the waypoints will be changed to reflect the new datum automatically.[/quote]

HI BaldEd & others

tryied this one and still no Go!!! GPS based on "Geod datum 49" on Garmin Vista download waypoints into a *.gpx file in MapToatster in PC up load this file to GPS then changed garmin to WGS84 then downloaded the *gpx file then imported into GE still out by about the same 50m to the SE of the points it seem reasonable constant for a GPS???

Is there away of caputre a waypoint that you can see the actual point and the adjust the rest of the waypoints to correct them to get a better fix?

you have got to be able to get a better fix in GE?

thanks

3dmax

[tgsnoopy]

I'm pretty sure, I read somewhere that no matter what datum your GPS is set to, the waypoints are always uploaded and downloaded in WGS84.

Based on that theory, the procedure just described wouldn't change any of the locations when the datum was changed to Geod49.

[GraemeWi]

I've found some of the GE images a bit off against accurate tracklogs I have - they are fine against LINZ data, but show a variance when in GE. As it stands I wouldn't use GE for this kind of work until the calibration is alot better. It is still an awesome tool for exploration and more macro level stuff!

[rediguana]

I'm pretty sure, I read somewhere that no matter what datum your GPS is set to, the waypoints are always uploaded and downloaded in WGS84.

Correct. When you change the datum on the GPS, that is only changing the way it is displayed, i.e. the GPS takes the default internal representation, and converts it to the desired grid just for display.

Hence if you want to download it and convert it, you need a tool like DNR Garmin to download, and then reproject the co-ordinates to the grid system of choice.

[3dmax]

So........wise Ones


If I can visually see the spot of where the Waypiont on GE should be then....how can I adjust my *.gpx file data to correct all the rest of the waypoints to what i belive should represent the Coods in GE?????

Any clues?

Thanks

3dmax

[rediguana]

If I can visually see the spot of where the Waypiont on GE should be then....how can I adjust my *.gpx file data to correct all the rest of the waypoints to what i belive should represent the Coods in GE?

I don't think it will be that simple unfortunately. The error in Google Earth imagery appears to vary depending upon the tile, and source of the imagery. This means that it isn't a consistent error that can easily be calculated and corrected for. Also, I'd personally have relatively more correct GPX co-ordinates than have it appear correctly on the imagery. One day they will likely update the imagery on GE, and it will be correctly geo-referenced and all you GPX will be inaccurate.

Cheers Gav

[rediguana]

I've started a related thread here.