Author Topic: google earth/survey overlay  (Read 577 times)

Offline woollydigger

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google earth/survey overlay
« on: August 14, 2018, 06:47:32 pm »
been trying to overlay the survey onto google earth from compass it state's to use UTM of which I've done but the survey is coming out about 20ish meters where it should be any help on what I'm doing wrong?
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Offline alastairgott

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Re: google earth/survey overlay
« Reply #1 on: August 14, 2018, 09:01:26 pm »
There was a similar request for help from Therion last year, have you used an accurate grid reference? would it be worth putting your grid reference into google earth or an online grid reference finder.

If it's coming out in the same (inaccurate) spot, it might be worth changing the coordinates to where the online grid reference finder thinks it should be?


https://ukcaving.com/board/index.php?topic=21946.0
"I can though see one big error. You need to use 5 digits on your grid ref. Using only 4 will put you cave miles away from where you want it. Also to make it fit GE you may have to fiddle around with the last numbers to place your entrance exactly where you want it. It seems GE images can be a bit distorted so quite often when you do surface surveys of roads, dry stream beds, and entrance to entrance etc they sometimes do not fit too well.

As for the code in your Th file I use this and it works.

survey ChurchPot

centreline

cs OSGB:SE
station 1.0 "main ent" entrance
fix 1.0 09959 76033 217
declination -1.4 degrees"

Offline woollydigger

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Re: google earth/survey overlay
« Reply #2 on: August 14, 2018, 10:26:12 pm »
Tried using a place pin on google earth and the coordinates of that both lat/long and also UTM but still giving me the wrong location I’m 9ish meters away from the entrance to the west
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Offline langcliffe

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Re: google earth/survey overlay
« Reply #3 on: August 14, 2018, 10:37:01 pm »
Tried using a place pin on google earth and the coordinates of that both lat/long and also UTM but still giving me the wrong location I’m 9ish meters away from the entrance to the west

I have had situations where a new version of a Google Earth set of images have displaced my pins by that amount. Since then, I haven't trusted Google Earth coordinates to be that accurate.

Offline mikem

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Re: google earth/survey overlay
« Reply #4 on: August 16, 2018, 06:07:28 am »
It also depends where the plane flew over, as distortion is greater towards the edges of the photos.

Mike

Offline MarkS

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Re: google earth/survey overlay
« Reply #5 on: August 19, 2018, 05:46:25 pm »
I've certainly seen big parralax issues in places. For example some vertical cliffs cover significant areas in the satellite images, which clearly isn't right, so cannot tie in correctly with any overlaid survey.

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