The Use Of Google Earth For Map References

[Mike from North Queensland]

At long last I have started to catalogue my collection with latitude and longitude grid references for the more important specimens. Most of which I used my GPS to reference. There were a couple of localities that were a little of the beaten track that I did not get back to too mark. So when I got home I used Google earth for those reference marks. When I checked those references with those marks I obtained myself there were about 200 metres variance. I then cross referenced my marks against a geological map I had of the area and confirmed that my GPS marks were accurate and Google earths were not.

My question is how does the accuracy of Google Earth’s map coordinates correlate to actual grid references in your area?

Is this inaccuracy a military error or is it due to alignment error.

Another point to ponder is the quality of the image that is available where I fossick in central Queensland Australia compared to some of the images over some of the capital cities. This I assume is a user generated thing as everybody looks at his house and very few use Google earth to look for fossicking sites.

Mike

[mzkleen]

I'm going to be doing the same thing myself with Google Earth. As for the accuracy of Google Earth's map coordinates, I haven't had the time to check that yet. I would think the inaccuracy is due to an alignment error.

There are more people that are using Google Earth now to look for potential fossil sites, such as old quarries, strip mines, etc. I am going to start using it for that purpose myself. There are a few members here that are using it for that purpose. It's a great idea.

Happy hunting Mike!

Judy

[erose]

I use Google Earth to mark collecting locations. As far as the accuracy is concerned I m not too worried about a tolerance in the hundreds of yards. All of my sites are also notated in a book with detailed descriptions of location and stratigraphy. If anyone wanted to explore my sites or should I have found something important that would be more important than a pin on a map with Long and Lat.

In the early days of GPS the signals were dithered by the US government to keep them from being useful to the "enemy". You had to have the code to un-dither if you wanted accuracy. They don't do that anymore. The accuracy of this stuff is always somewhat suspect. By example my wife's new IPad has our location as the house next door. Maybe 200 feet NE. I'm still trying to figure out how to correct it.

The aerial photography they use can be dated and the resolution pretty bad depending on how old it is. Here in the US I can barely discern a house on some images of upstate New York and in others I can see chairs on decks. Obviously remote areas are not being re-imaged as often. One cool thing no is that the old maps can be selected so you can go back and see how the area has changed.

All this GPS stuff is fairly new but getting better day to day so I wouldn't get hung up on 200 meters yet. Now I do realize that in some localities and terrains that could make the coordinates worthless. So once again we need to be redundant and keep written notes made from real observations to back up our data files. Heaven forbid Google earth should ever shut down.

[Vordigern]

if anyone figures out how to correct this please post it, Ive been trying to use coordinates from some published papers to search for fossil sites (mostly in streams) but google maps seems to be far to inaccurate to be any real help

[erose]

if anyone figures out how to correct this please post it, Ive been trying to use coordinates from some published papers to search for fossil sites (mostly in streams) but google maps seems to be far to inaccurate to be any real help

There is a bit of a myth that the new electronic maps are going to be extremely accurate. All flat maps are a distortion of the truth (the earth is a sphere not a cube). All maps need to be ground-truthed and then are only as good as the original base point (or whatever they call it).

I would also suggest that coordinates published in older papers are probably just as questionable. USGS topo maps are/were not always accurate. Only a given percentage of the map was actually measured first hand. The rest is a best guess (SWAG) created from aerial photographs and whatever else they can gather to work from in the drafting room.

Same with geologic maps. The workers went out and took as many measurements as time and budget allowed and then stitched it together as best they could. They might assume a level of dip across a distance that in fact changes in between. You have to match what the map suggests against actual observations where you are standing.

As far as I know the us government is no longer dithering satellite signals. The accuracy is more a factor of how many satellites the GPS receiver is seeing and the quality of it's internal software. Some products are obviously better than others. We have Garmins in our autos and they can be spot on as best I can tell, or they can be totally confused not even being able to tell me what state I'm in!

[Herb]

What is Really cool about Google maps is the street view, where you can drive down the road and see the roadcuts.