Lat/long from google earth on 2 visible objects roughly 100' apart, or lat/long from Garmin hand held gps to .001 minute on same objects? Which would you rather trust If thats all you had? Not for anything exact, just to get close to something you can calculate from those 2 points about 500' away, to locate with the garmin to start looking.
Doing some quick math I came up with about 6 feet error on the garmin. Isn't google earth like 30 feet per pixel? I dunno, I'd go with the garmin I guess.
Should add theres about 15' difference in the 2, and the garmin locations are skewed slightly from GE. And object being looked for is under about 60' of water.
eddycreek, post: 453993, member: 501 wrote: And object being looked for is under about 60' of water.
[SARCASM]Oh, this oughta' be good![/SARCASM] 😀
R.J. Schneider, post: 453995, member: 409 wrote: [SARCASM]Oh, this oughta' be good![/SARCASM] 😀
Yeah, guy I know works for a diving company and they sre looking for the upper end of an old pipe that was used as a bypass while a dam was constructed. It was capped off and covered with dirt when the dam was finished, now its leaking and they need to find the upper end and seal it up. Lower end is capped too, so they know about where that is and about where it starts under the dam. Just trying to figure out about where to start looking. They have a drawing showing the pipe stations with several deflections, but it apparently wasnt tied to the control for the dam.
eddycreek, post: 453997, member: 501 wrote: Yeah, guy I know works for a diving company and they sre looking for the upper end of an old pipe that was used as a bypass while a dam was constructed.
ah! okay, i had a flashback of setting points in water last week. I thought this was some kind of boundary exercise.
Many of the photos in GE are not Ortho's - so height plays a part in locations - a GPS reading would not have this bias
You are probably saying 60ft from shore and not 60ft deep.
I've used my Shonstedt off the bow of an aluminum boat and found things several feet deep.
I pick fence corners and scaled distances off GE to plug into my handheld Garmin to get me close enough to scan a 50ft circle if necessary and usually am within 10ft.
Be sure to set your handheld to WGS84 to correspond with GE.
Depends.
Does your state or local GIS have rectified orthos?
Does the Garmin have waas? 6 feet sounds good unless the quality is still +/- 30.
What about opening the cap on the down hill end and looking for the whirlpool? Might not work for a slow leak.
What about calling a septic service to run a tracer up the pipe? We use a sanitarian who has one and he can find pipes under 6 to 8 feet of dirt. Probably could do better through water.
I had an intern who was making autonomous robots for a school project. Servo motors and other sensors could map the pipe location to the cap... you know, for a small fortune of r&d...
No
A Harris, post: 454012, member: 81 wrote: You are probably saying 60ft from shore and not 60ft deep.
I've used my Shonstedt off the bow of an aluminum boat and found things several feet deep.
I pick fence corners and scaled distances off GE to plug into my handheld Garmin to get me close enough to scan a 50ft circle if necessary and usually am within 10ft.
Be sure to set your handheld to WGS84 to correspond with GE.
No, Water is 60' deep and another 15-20' of earth over that. The outlet end was covered with a concrete cap some time ago, so it is inaccessible and approximate. Leaking about 100 gal/minute.
How big is the pipe?
Can they plug from inside?
We use Garmins with wass at work extensively. Compared to RTK surveyed points I have very rarely seen them over 10?? off. Most of the time they are within 5??.
GE he has gotten very good in some places and might be better, but you'd need to check the specific area.
Set the Garmin to decimal degrees to get the best resolution, and average a waypoint for as long as practical. I did a lot of testing several years ago and found this gave results more often within a few ft but occasionally still 20 ft off. Very long averages approached a granularity of 2.5 ft in those models due to some internal computation precision.
Unless recent models have improved the datum transformation, it won't matter whether you set WGS84 or NAD83, you'll get WGS84 because they used a null transform in the ones I played with. Check by setting a few waypoints in one datum and then switching to display them in the other datum.
What works for me is etrex and use the averaging option on Dave waypoint. I let it average for an hour. And that's better than google earth.
In the Portland area there is lots of historical photography on GE. or the last 20 years of so there is photography at least every 2 years and sometimes more than once in a year. And I use GE as a poor man's GIS to track my jobs and control points.
But if you set a placemark/waypoints at a specific lat/long and then step through the historic photos you can watch the background dance around. On some photos a control point in the corner of a sidewalk will be in the sidewalk, in the next it will be out in the middle of the street, the next inside an adjacent building. And if you didn't have any landmarks to go by you would never know how imperfect the one you are looking at now is.
Some sets of GE photos are well rectified, others are little more than cartoons. There is no metadata on GE. So I'd be going with the Garmin. At least then you have some reasonable idea of the error you've got at any given time.
eddycreek, post: 453987, member: 501 wrote: Lat/long from google earth on 2 visible objects roughly 100' apart, or lat/long from Garmin hand held gps to .001 minute on same objects? Which would you rather trust If thats all you had? Not for anything exact, just to get close to something you can calculate from those 2 points about 500' away, to locate with the garmin to start looking.
Distances and bearings on the legal description, or locating the monuments on the ground? (Or maybe both.)...oh wait, that wasn't the question...sorry.
I don't have an educated answer to your question, but this is an interesting project. I would love to here the final outcome.
eddycreek, post: 453987, member: 501 wrote: calculate from those 2 points about 500' away, to locate with the garmin to start looking.
I didn't pay enough attention to this part of the OP. If you measure 3 points with the Garmin with say a 2 or 4 minute average on each and as little delay as possible between, the relative positions will be much better than the absolute positions. If you measure a couple points, go home and calculate, and come back later to stake out a search position, you won't do so well in relative positioning.
eddycreek, post: 453993, member: 501 wrote: Should add theres about 15' difference in the 2, and the garmin locations are skewed slightly from GE. And object being looked for is under about 60' of water.
So you are taking positions 100' apart and extrapolating in a straight line 500' away? So the error in azimuth (direction) will be multipled fivefold.
Isn't diving really expensive relative to using some basic survey equipment like a total station or RTK GPS?
I would have thought it would be worth the extra cost to start looking as close as you could?
