CAD Northing-Easting Values
Dear Sir or Madam,
I recently came across a comment by Autodesk that the N_E values are "local" type. Perhaps this explains why they do not update when the coordinate changes, unless the point is moved. But at the same time, if the software only imports grid data, it seems to be a conflict with this concept. It seems that the only way to calculate grid northing-easting and therefore, read the datum and projection, is to use the survey database or the transformation tools. Without engaging those tools, it seems that Civil 3D is not making use of the coordinate system, even if it is set up.
Does anyone have an idea that can explain better Civil 3D behavior?
If you import a N, E, autocad will display the Lat, Long, coordinate value associated with that N. E. as defined by the projection you set in the parameters. If you change the datum, it will display the Lat. Long coordinate value associated with that same N. E. by the new projection you just picked.
If you wish it to behave differently in some way you probably should purchase a different program such as Trimble TBC which can be geographically based. However, you will still need to relate the position you want while using the different projections you wish to keep switching back and forth from and to. Why you want to do this is the much bigger question.
Hi @cturlington,
"N_E values are 'local' type." Northings and Eastings only indicate a rectangular coordinate system.
"they do not update when the coordinate changes, unless the point is moved."
What do you mean "when the coordinate changes"?
"if the software only imports grid data, it seems to be a conflict with this concept."
What do you mean by "grid data"?
"the only way to calculate grid northing-easting and therefore, read the datum and projection, is to use the survey database or the transformation tools."
In Civil 3D the coordinate reference system is assigned, not read. You need to know about your data before doing anything with it.
"Does anyone have an idea that can explain better Civil 3D behavior?"
I'd like to suggest a college course. There's also books available, YouTubes, this forum, the Civil 3D Forum...
https://forums.autodesk.com/t5/civil-3d-forum/bd-p/66
Dave
davidgstoll,
What do you mean "when the coordinate changes"? There are some designers and engineers in my department who do not set coordinates or set the incorrect coordinates in the file, and I wonder, as an academic exercise for my own understanding, if this lack of concern for coordinates really has had any impact since the software does not seem to update it anyway. As engineers and designers, I know we do not report or show lat-long values, only northing-easting values. So if the northing-easting is not updating, there is no way to know if they are incorrect or not, and they will remain as imported. Unfortunately, as non-survey practitioners, we do not subscribe to the Trimble Business Center.
What do you mean by "grid data"? Projected, flat, on the grid as opposed to on the ground.
My purpose is not to change coordinates/datums and projections but to understand the behavior of the Civil 3D software and get feedback from surveyor practitioners who likely know more about the subject than I do. I have read many books and watched many webinars over the years, but there are always small areas that still do not make a lot of sense.
"get feedback from surveyor practitioners who likely know more about the subject than I do."
...you'd be surprised.
I always point to some of Van Sickle's lecture notes (specifically Lesson 5 & 6) as a great primer for coordinate/datum questions:
