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My control is WAY off of orthophotos, why?

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(@mightymoe)
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@dave-karoly

This is similar to the datasheets I have for control nearby. One thing I've noticed with new datasheet downloads is that under superseded control values the NAD27 no longer shows. I was recently looking at one, in fact it was one of the base points for the triangulation network and NAD27 was not there. 

 
Posted : 03/02/2020 8:59 am
(@dallas-morlan)
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@sapperpels

Welcome to rplstoday.com!! As you may have noticed this is a helpful group.  However, be warned there are a few jokers in the deck!

 
Posted : 03/02/2020 9:01 am
(@bill93)
Posts: 9834
 
Posted by: @mightymoe

@dave-karoly

One thing I've noticed with new datasheet downloads is that under superseded control values the NAD27 no longer shows. I was recently looking at one, in fact it was one of the base points for the triangulation network and NAD27 was not there.?ÿ

Which one?

Note that NAD27 is given on the one discussed above.

You can also go to https://www.geocaching.com/mark/ ?ÿ?ÿ Enter the PID, fetch the geocaching page, and then click on "Original Data Sheet" to find a snapshot of the NGS sheet from about 2000.?ÿ That's sometimes handy to see what what the updates have done for a mark.

 
Posted : 03/02/2020 9:23 am
(@mightymoe)
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@bill93

The PID is PW0582, it is the SE base point, not sure why but the datasheet shows it as third order. 

 
Posted : 03/02/2020 9:47 am
(@dave-karoly)
Posts: 12001
 

@larry-scott

It is also a 3rd order Tri station.  Those often have several feet of error (at least here in Plate Boundary Land).

 
Posted : 03/02/2020 10:26 am
(@dave-karoly)
Posts: 12001
 

@mightymoe

PW0582                          SUPERSEDED SURVEY CONTROL
 PW0582
 PW0582  NAD 83(1986)-  44 54 45.71582(N)    107 10 23.21701(W) AD(       ) 3
 PW0582.No superseded survey control is available for this station.

Wow, I've never seen that before.
 
Posted : 03/02/2020 10:27 am
(@bill93)
Posts: 9834
 
Posted by: @mightymoe

The PID is PW0582, it is the SE base point, not sure why but the datasheet shows it as third order.

Oh, but note that PW0502, less than a hundred yards north, has the same name, is 1st order, and has superseded NAD27 data. It was monumented in 1925.

Note that PW0582 was monumented by USGS.?ÿ I'm guessing it didn't have a designation or coordinates in the CGS system until it got tied in much later.

 
Posted : 03/02/2020 11:01 am
(@mightymoe)
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@bill93

You are correct Bill, that's odd, not sure what that point is. Either RM 2 or one of the bench marks along the highway. 

There is a story for that, but I don't know what it is.

SE base is a point used by everyone during the NAD27 days, it's one of the two base point for all the surveying. 

It isn't a great point for GPS but I think we may have located it RTK at some point.

This is the only datasheet I've ever used for it:

 
Posted : 03/02/2020 12:56 pm
(@geeoddmike)
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The NGS provides a tool to solve the forward problem: solving for an unknown pointƒ??s given starting geographic coordinates, geodetic azimuths and ellipsoid distance here:
https://www.ngs.noaa.gov/cgi-bin/Inv_Fwd/forward2.pol

?ÿ

12FA1D76 0F8F 4A71 B2DD 8EDE8BB78BF0

Also the old 1984 standards and specifications document give the following tabulation of horizontal accuracy for points determined by what are now known as ƒ??classical geodetic methods.ƒ?

73243792 3A75 4868 BCDF D45467B2853B

?ÿ

 
Posted : 03/02/2020 6:24 pm
(@whh114)
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From the information that you provided, you are using two different datums (NAD83 and NAD27).?ÿ You would have to convert the NAD27 to NAD83 and that is not accurate. As far as your orthophotos not lining up, I see this all the time.?ÿ Our orthophotos are on the Grid (NAD83) and they line up when I have scale factor in the Data Collector. If you come off of two GNSS points and then traverse with a total station on the ground, and over long distances, you will come off the orthophotos significantly. In order to correct this problem, one possible solution is to get another surveyor to set GPS control on your job site. You can even get inexpensive receivers to collect data and then send to OPUS. I don't see a solution at this point by manipulating your data. I wrote an article about the Grid to Ground Correction and you can find it here if you want to read it for reference: https://www.xyht.com/surveying/grid-ground-project/.?ÿ Best of luck to you.

 
Posted : 04/02/2020 8:01 am
(@larry-scott)
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@whh114

he didnƒ??t make a huge mistake. He accidentally used geodetic azimuth. He found that out, used the proper grid az and the pub NAD83 position. Just a simple input error, that was apparently (to me imo) the most likely issue, in his first post. Iƒ??m sure heƒ??s applying the proper SF. He only traversed 1200 feet.?ÿ

?ÿ

 
Posted : 04/02/2020 10:27 am
(@nate-the-surveyor)
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Many surveyors are NOT familiar with things they do not use every day. Recently, I observed a surveyor, who was not familiar with an area he practiced in. He blundered, in procedure, and caused havoc. I have my blind spots too.

N

 
Posted : 04/02/2020 3:22 pm
(@larry-scott)
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@nate-the-surveyor

Traversing 1200 ft from a pub disc in SPC is not exotic. Not in the 21st c. 

He had a brain fart. 

 

 
Posted : 04/02/2020 3:41 pm
(@nate-the-surveyor)
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@Larry Scott, brain fart @10:00 noted.

Sometimes another set of eyes is beneficial. It's even more of a problem for solo practioners.

Nate

 
Posted : 05/02/2020 4:52 am
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