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Google Earth imagery and “surveying”
About 6 months ago I prepared some R/W docs (from a field survey) and, at the last minute, discovered the scope of the run was larger than the W.O. indicated. It was a “fast track” and an hour west of here in the “gulag” of the service area I work in for a local rural electric coop. Rather than blow the entire next day for additional field work I did something I have always avoided. I placed a GE screen shot under my drawing and extended the proposed R/W form the “manufactured” field work. I reasoned I should be able to fit an existing pole line within a 30′ wide easement. Maybe not centered, but contained within a 30 foot wide swatch.
In my defense I am extremely familiar with the use of aerial data from my days with the Highway Dept. Getting an image scaled and rotated (I avoid “rubber-banding”) to fit ground data is truly half science and half art. My only suggestion to others attempting this would be to only work off known distinct points shot in the field that appear in the image.
Anyway, I was back out there earlier this week and took the time to actually shoot everything I avoided six months ago. I was happy to find there was only about a 3 minute error which equated to a positional difference of less than 2 feet in a 2000′ run. It worked out this time.
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8 Replies
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Ah…The Black Arts of Surveying
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A month ago I got a job to split a W2 of a section north and south of a county road. I knew the area, and I figured it’s a piece of cake. Then I groaned when I saw where it actually was. It contains a series of curves to avoid the head of a valley where a ridge creates a watershed divide. Of all the spots along that road it is the worst possible place. I figured looking at Google there are 6 curves. So I sat down on Google one Saturday and plotted them up. Put it into my TBC, then into my ACAD drawing and sent the crew out to stake it,,,,,,,,if it worked. I didn’t have all that much hope, PC came back and said he couldn’t use it and had located all the centerline and fences. Turns out the Google plot was very close, I didn’t adjust hardly any of it except the 2 larger curves. The Google plot was better than expected and easier than I thought once I figured out how to move from Google to ACAD. His CL shots were often within a foot of my Google plotted points.
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I used Google Earth extensively for checking photogrammetrically derived topo mapping. Dive in to “Street View” and walk down the road, looking left & right, up & down for missing manholes, overhead wires, ditches, water valves, structures, electric vaults, hydrants, drainage inlets, gates in fences, low walls, et. al. It was surprising how much “stuff” the photo boys missed, much of which was plainly visible on the ortho-rectified photos.
Needless to say, I was not well liked by the photogrammetry dept., as my time and their revision costs were charged to their budget. They even had the gall to complain to corporate that I was spending too much time checking their work (that I was “slow”), compared to my predecessor. Well, he found very few errors, 10-20 per project while I’d find 100s. You get what you pay for.
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???
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Along with that philosophical question is one I’ve often pondered over. Should you improve a bad situation and become responsible for it when you can’t make it really right?
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Along with that philosophical question is one I’ve often pondered over. Should you improve a bad situation and become responsible for it when you can’t make it really right?
I’ve learned in my old age to avoid stepping in ‘survey’ dookie. You can’t make a silk purse out of a sow’s ear. All you can do is show what’s out there and where and why you set YOUR pins.
PS -I have noted on survey plats something to the effect “This area is all screwed up. If you think you can come up with a better solution get after it.” 😉
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Yup. The only concern I have is ancillary maps where a valid Record of Survey (or equivalent) is overlaid on Google Earth/GIS/local non-orthorectified imagery and purports to show local topography (fences, ditches, roads) where the imagery is distorted sometimes by dozens of feet, mostly due to uncorrected relief, or the survey was not registered against the imagery accurately, so the boundary lines are shifted or rotated in a gross manner so the situs is not shown correctly.
Official maps with precise bearings and distances and ties to State Plane Coordinates should never be overlaid with imagery unless a photogrammetrist is involved who can assert accuracy standards (or a bullshit disclaimer is on the map). That being said, Google Earth, etc., is a fantastic reconnaissance tool for land surveyors to get into the ballpark. Clearly most states require 2bit black&white only map submissions for filing. Grayscale, dithering, etc is not permitted which means no imagery allowed. That’s fair; I’ve requested .tiff files of record maps that got through with imagery overlays which blacked out all the annotations along the lines and were useless. The Recorder threw up her hands and said the original was lost (poorly digitized by some clown contractor), deal with it.
Frankly, I think an ink on Mylar submission of record maps should be the law immemorial. Yah, photocopy it, digitize if for distribution, etc., but in the courthouse vaults there should be the original, unalterable even by devious means (electric erasers leave traces) in clear linework and plain English annotation that can be read by eyes on a piece of Mylar or vellum.. There’s “modernization” efforts in many Counties afoot, ACAD & MicroStation submittals allowed, but I want to see the actual original, with wet stamps and imprints from my actual stamp, if the sh*t hits the fan.
Sorry,I’m old school.
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You can go back and forth between Google Earth and TBC. From TBC go to Google Earth with a kml file. You can shift the kml to fit the Google Earth image. Just shoot a few distinct points that you can see in Google Earth (fence corner, curb corner). Shift the kml output until it matches over your “control points”. Once you do that things usually fit up very well (maybe not so good in very steep country). Once you are fit up you can also draw in Google earth and then export back into TBC. These are great tools.
If you use the full capability of TBC you can get rid of your ACAD. Full drafting can be done in TBC now. I don’t own or use any current version of a CAD program. All I need is TBC.
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