SURVEY DATABASE COORDINATES-EXPORTING-IMPORTING

[CADEngr2014]

Hello,

I am using Civil 3D 2015.

I was just made aware of the coordinate system settings inside the Survey Database module.  I was concerned with past survey point databses that did not have the coordinate system set properly.  So I re-imported all my survey points and deleted the old history from the databases.  The new imports were from source csv files from the surveyor, so I know they were not modified in any way.  Once re-imported, I compared the new point locations with the old dabase point locations and they appeared to be in the same location.  I did not have the same luck comparing exported (csv file format) non-coordinate survey database points to coordinate survey database points.  In conclusion it appears that the discrepancies with coordinates are occuring on exporting points from a non-coordinate survey databse rather than importing points.  It seems like errors should occur on import or export if the coordinate system is not set in the survey database.  Has anyone had a similar experience and know why exporting from a non-coordinate survey database would reflect error in point locations but not show error on point locations when import into same database?

[lucy.kuhns]

Take a close look at the coordinate value differences you are seeing and make sure that it is not a US Ft to International Ft error.

[CADEngr2014]

Lucy,

You are correct, the default survey database coordinate zone setting is "none" but the distance setting is international feet.  I believe what must be occuring, is the coordiantes in my case, are only set to 4 significant digits.  So 2 ppm will not show-up as a change in location between international feet and us survey feet.  So if I just toggle the survey data base to the correct coordinate, any shift or change in location will be negligible and not measurable given the level of accuracy in the native coordinate.  I tested this theory and found after toggling the database to the correct coordinate, the exported poinbnts had the same northing/easting values to 4 digits beyond the decimal.  Does that sound correct?

[lucy.kuhns · Accepted solution]

When you imported the CSV into your survey database there would be no effect of units settings - so values will be exactly the same. But if you take that same CSV and import it into a Civil 3D drawing first, then bring the points from the drawing into the survey database the units setting will have an effect. And it could show up as a very small difference as US SUrvey FT to International FT, or as a great difference such as feet to meters:)

[lucy.kuhns]

Thank you CADEngr2014.

[Pointdump · Accepted solution]

CE14,

In addition to Lucy's excellent points, also make sure the Transformation Tab in Drawing Settings is disabled whenever you are using the Survey Database.

Dave

[dcutter]

So... I'm working in Civil 3D 2017.

I just ran into this issue again with data that we are very familiar with.  We have a site that we have been monitoring for several years.  Every couple of years we conduct a survey.  We have surveyed in 2011, 2012, 2014 and 2017.  We started using the survey database for this project late in 2014.  We recently started to compare the 2017 data to the 2014 data and we saw a 4 foot shift.  

What we tried:

The coordinate system in the survey database was ID83-CF, survey feet.

The coordinate system in the target drawing was also set to ID83-CF, survey feet.

When we did this, we noticed the Northing and Easting did not match the Grid Northing and Grid Easting.

What worked:

We set the coordinate system in the survey database to ID83-CF, survey feet.

In the target drawing, we did not set a coordinate system, but we made sure the units in the drawing settings were set to survey feet.

We inserted points from the survey database into the target drawing.

Once we verified the points were located correctly, we assigned the ID83-CF coordinate system to the target drawing.

When we did it this way, the Northing and Easting matched the Grid Northing and Grid Easting and all the data matched the survey file we were given.

[Pointdump]

Denis,

"...compare the 2017 data to the 2014 data and we saw a 4 foot shift."

Details on data collection please. Total Station or GPS? Same NAD 83 Datum? HARN, NSRS?

"...the Northing and Easting did not match the Grid Northing and Grid Easting."

Best to always turn off the Transformation Tab when importing points from Data Base to Drawing.

Dave

[dcutter]

In this instance the data collection is irrelevant.  I'm starting with a simple txt file.  If I made up fake data in a CSV file and imported it through the survey database as prescribed, I would still get the shift in the data.

That said, on site they are using a Total Station tied to well established ground control in a local grid system.  Then they are transforming that local grid to State Plane NAD 83 U.S. feet. EPSG 2242.  We receive the data in the office as comma delimited txt file.

We don't use the transformation options from the Transformation tab of the Drawing Settings.  During my trouble shooting I ensured this was turned off in the active drawing during the initial survey import event and in the target drawing.

What we may be seeing is a difference between the way Civil 3D handles coordinate systems based on how they are assigned.  As a matter of course, we use MAPCASSIGN to assign coordinate systems.  I have had some users describe different results if they assign a coordinate system through the Drawing Settings.

[Pointdump]

Denis,

"...we use MAPCASSIGN to assign coordinate systems. I have had some users describe different results if they assign a coordinate system through the Drawing Settings."

I got schooled recently on the use of _MAPCSASSIGN, which is my preferred method of assigning a Coordinate System. Please see <<<This Post>>> from @Mike.M.Carlson for some subtle distinctions in how C3D handles International Feet and US Survey Feet.

Dave