Bing Aerial off 4-feet from our coordinate system?

[sbsomers]

I have a project that has proven that we know very little about how the coordinate systems work in Civil 3D. I've been reading up about how Civil 3D uses coordinate systems, but I haven't been able to nail down the problem in my particular case. Here's the situation:

We originally surveyed the project based on ground coordinates, but when a biologist got involved, they wanted our drawing in California State Plane II coordinates (our local coordinate system) so they could line up their wetlands correctly. Our surveyor translated and rotated his boundary and cogo points to State Plane and I subsequently shifted our aerial survey (XREF XPLN in the attached zip file). However, when the biologist tried to import our CAD work into their GIS system, they found that it was off by about 4'. And I'm getting the same result when I use the GEOMAP through BING (see the screenshot below where our building outline is purple and off by about 4').

But it gets more confusing. After some fiddling around, when they created a kmz file from our CAD linework and then imported it into Google Earth, it appeared to line up perfectly. Then exporting it from Google Earth back into their GIS software had everything line up perfectly on their end. They said the issue appeared to be in the difference between NAD83 and WGS84 which I know nothing about. Thinking we had it worked out, I had them export their wetlands with our boundary so I could bring them into our XPLN drawing. But when I did (even after switching their drawing to CA State Plane in the drawing settings), it still came in differently - in this case about 17' off (the yellow linework in the image below). 

I think I'm operating out of my league when it comes to coordinate systems, as I'm at a complete loss as to what's going on. Our surveyor said he's checked and double checked to ensure his coordinates are in State Plane II as they should be. Is there anyone who can offer a solution? Files attached below.

Thank you,

Shawn

[Pointdump]

Shawn,

The quality of Bing Live Maps has gone down recently. Read about it <<<Here>>>. As a check, you can add <<<ArcGIS for AutoCAD Plug-In>>>. The ESRI imagery is better, but it's slower than Bing. Another option is to see if you have imagery available for your area of interest on websites like <<<This One>>>. The point being, when things don't line up, have several checks to find out what is wrong.

There are several versions of State Plane -- NAD83 (1986), NAD83 (HARN), NAD83 (2007), NAD83 (2011). California Tectonic Plates are moving pretty fast, so Datum selection is important. So when your Surveyor says he's in "State Plane", ask him which one:

Dave

[rl_jackson]

Also, to add to what @Pointdump suggested, you can always download most aerial ortophotos from USGS at https://earthexplorer.usgs.gov/.

[Anonymous]

While there could be some error in conversion from StatePlane to LL, were the correct number of significant digits used for example, using a aerial, especially from Bing, as "correct" to check your survey against is poor practice.  Even a high quality image, in a correct spacial system still has many factors that could throw it off, such as skew and camera angle. 

The difference between matching in Google vs Bing could simply be better spacial calibration of the images by google.

Points are points and the math is the math.  If the math is done right, and the images don't line up, 99% of the time, it's the image.  Corps of Engineers has a tool called corpscon.  You could use it to double check the transformations being preformed.

As others have suggested, load images from various sources and compare.

[Mike.M.Carlson]

Hello Friend-

If I can chime in here.  I respectfully submit to the group that the issue SSOMER is having is dealing with units conversion between International Feet and US Survey Feet.  I noticed in his  "XREF XPLN-State Plane.dwg" he had the Civil 3D drawing settings\Units/Zone\Set AutoCAD variables to match option checked:

Furthermore, his XREFs for the Existing Site Feature XREF had the correct coordinate system defined, but his UNITS were set to International Feet. 

 

Therefore, when he attached this file to the XPLN-State Plane dwg, that drawing was doing a International Feet to US Feet conversion.  The difference between International foot and US Survey Foot is very small, but when you factor in State Plane Coordinates, that conversion could be significant.  Therefore, I think that is what is going on here.  The US Survey Foot Unit is new to ACAD 2017, so older drawings set to FEET (which refers to International Feet) could be affected when you attached to DWGs set up in US Survey Feet

.

When I set the Existing Site Feature XREF to no datum no projection and set ACAD units to unitless and re-attached to the XPLN-State Plane dwg and turned on Bing, it all lined up.

I have attached .zip file containing the files I used to get Bing to work. 

I hope this helps.

[BushW]

Hello @sbsomers

I'm just checking in to see if you need more help with this. Did the reply of @Mike.M.Carlson provided work for you?

If so, please hit the ‘Accept as Solution’ button if/when relevant so, that others can more easily benefit from the information and thank you for doing so. 

Best Regards,

Wendell

[fcernst]

found that it was off by about 4'...

Yes, we had this property below surveyed to State Plane last month, and Bing Maps comes in shifted 4' to the West:

[Pointdump]

Shawn,

To add to Mike's excellent post, one way to verify if you have an International/US Survey Foot problem is to multiply your coordinates by 2 PPM (.000002). That way you can tell exactly the length and azimuth of the shift.

I don't have any version of Civil 3D right now to check your attached drawing.

Dave

[sbsomers]

Hi All,

Perhaps I should have been a little more specific with the problem. The problem isn't really that I'm trying to get an aerial photo to line up with my linework (though that would be nice). The problem is that the projection for the wetlands drawing we received from our biological consultant is off from our coordinates (their file is the “BradyAtVineyard_Waters_Site” drawing).

Thank you to maroncarlson007 for pointing out an additional survey to int’l foot conversion that I missed (I thought I got all of those), and it does appear that now when I xref the wetland drawing it will come in right over the aerial imagery (if I could get that God-forsaken Bing aerial feature to work more than 10% of the time that is), but there’s still the issue of there being a 4’ discrepancy between our “XREF XPLN-State Plane” and the “BradyAtVineyard_Waters_Site” xref we received from the biologist. I’m trying to figure out where that difference is coming from, and I’m really confused. And I’m trying to determine whether there is a certain projection that takes this 4’ difference into account or whether we need to move our CAD linework to match.

As mentioned in my original post, the biologist said that 4’ seems related to the difference between NAD83 and WGS84. The biologist’s specific comment was: “We have re-projected our data in WAS-1984 for your use (attached).  It seems that (again according to my GIS Guru friend) in 1983/1984 these two projections were very close, but that every year they get farther apart do to corrections that occur on an annual basis.”

Like I said. I’m in over my head on this and we have another project with them that I need to be sure lines up correctly. If anyone can help me navigate this issue, I would be grateful.

[Mike.M.Carlson]

Hi-

Then it must be a datum transformation issue like Dave brought up earlier.  How was the Geometry in the XREF XPLN-State Plane drawing created?  Was that the linework the surveyor converted from Ground to SPC Grid?  You would need to know what his NAD83 Datum reference is (or specifically what  NAD83 epoch or realization he's using). 

Once you know that, you can also ask the biologist what their GIS mapping projection assumption was before they re-projected to WGS84.  There are actually a lot of WGS 84 realizations too, and ArcMap has a bunch of options to convert between datums.  The trick is to match up the GIS datum to your surveyor's NAD83 Datum, but without specific datum metadata, it will be hard to correlate.

[Mike.M.Carlson]

As a follow to my post about datum transformation issues and @Pointdump 's earlier post,   The following NGS white papers briefly discuss the evolution of ITRF / WGS 84 and NAD 83.  I hope this helps.

Snay, R.A. & T. Soler (1999). Part 1 - Modern Terrestrial Reference Systems. Professional Surveyor, 19(10), 32-33.

https://www.ngs.noaa.gov/CORS/Articles/Reference-Systems-Part-1.pdf 

Snay, R.A. & T. Soler (2000). Part 2 - The evolution of NAD83. Professional Surveyor, 20(2), 16, 18.

https://www.ngs.noaa.gov/CORS/Articles/Reference-Systems-Part-2.pdf

Snay, R.A. & T. Soler (2000). Part 3 - WGS 84 and ITRS. Professional Surveyor, 20(3), 24, 26, 28.

https://www.ngs.noaa.gov/CORS/Articles/Reference-Systems-Part-3.pdf

Snay, R.A. & T. Soler (2000). Part 4 - Practical considerations for accurate positioning. Professional Surveyor, 20(4), 32-34.

https://www.ngs.noaa.gov/CORS/Articles/Reference-Systems-Part-4.pdf

[sbsomers]

I will have to bring this to our surveyor and see how he ended up with his coordinates.

Thank you for the suggestions.

[Mike.M.Carlson]

Right on man...good luck.

Thanks,

[Pointdump]

Mike,

Thanks for the links. Good reading! I put on a pot of coffee and enjoyed reading all 4.

Dave

[Mike.M.Carlson]

Thanks Dave!  I had a feeling you would like that oldie, but goodie!  

Here's another night table reading option I have found helpful 🙂

Mike

[BushW]

Hello @sbsomers

Did @Mike.M.Carlson help resolve your issue with the great suggestions? If so, please reward the post that worked with an ‘Accepted as Solution’ and pleases also mark a post or posts as Accepted Solution(s) that resolved the issue or answered your question so, other Community members may benefit and thank you for doing so, and I'm here to help.

Best Regards,

Wendell

[sbsomers]

I have not been able to resolve the issue yet. I don't even know where the heart of the issue rests. I've forwarded these suggestions to our surveyor and I don't know if he's had time to look into it fully.

[fcernst]

More than likely due to the different datums used as you were told (see second image below), simple as that. 

As far as Bing Maps becoming degraded and shifted...Autodesk has already acknowledged that (first image below).

e

[BushW]

Hello @sbsomers

---

@Anonymous wrote:
I've forwarded these suggestions to our surveyor and I don't know if he's had time to look into it fully.

---

I just wanted to follow up here, any feedback on the issue from the surveyor. Did you have the opportunity to review @fcernst post on this issue? Please keep us updated on this problem. Thanks

Best Regards,

Wendell