If you are familiar with the coordinate systems in Civil 3D, you may be aware that the transformation tab allows you to transform a local coordinate system to a known coordinate system. In other words, Ground (project coordinates) to Grid (known coordinates). Now, how does this tab affect bringing survey data into the survey database? Well, it all depends on where the data is coming from.
<begin disclaimer>I am not a surveyor nor do I pretend to be one on TV. I’ve just learned a lot about this stuff in recent years. I’m by nature an engineer and engineers aren’t allowed to play with survey data so everything I have, I made myself.<end disclaimer>
So what happens when you have transformations set to your drawing and you import survey data from a point file? Well, point files typically don’t have coordinate systems assigned to them (can they ever?). When using the import survey command, the points come into the database as if they were collected using the same coordinate system as the survey database. Since I live in Colorado, I’ll use NAD83 Colorado State Planes, North Zone, US Foot as the coordinate system. I create a point file that has the following points in it:
The survey database has the same coordinate system as the drawing, NAD83 Colorado State Planes, North Zone, US Foot and has a very simple transformation assigned to it. Basically, it will translate the ground coordinate N=40,000 E=50,000 to the grid coordinate N=1,040,000 E=3,050,000. When the point file is imported into the survey database, the points are brought in and the transformation settings in the drawing are not honored. I don’t know exactly why but, this is my theory on what is happening. When you bring the points directly into the survey database, they don’t come into the drawing and then into the database, they are brought directly into the database from the point file bypassing the drawing altogether. Since the point file has no coordinate system (yet alone a transformation setting), they are simply brought directly into the database.
As you can see, the points coordinate match the points in the point file and do not reflect the transformation settings. If you need the points to honor the transformation settings, import the points into the drawing first, and then import the points into the survey database from the drawing. Since the points are in the drawing, the settings of the drawing will be used and the points will be transformed as they are brought into the database. In this image, you can see that the points in the drawing are in the project coordinates:
And after the points are brought into the survey database, they are in the known coordinate system:
Hopefully, this will help clarify some of the mystery of the survey database.