Assign Coordinate System - Grid & Ground

[riverdeer]

Do I assign a coordinate system? We have embankment drawings that we get from our land surveyor. They have both Grid and Ground point conversion table on it. The drawings are done in ground, which are derived by applying a scale factor to State Plane Grid. When I start a new drawing to insert these points, should I apply a coordinate system. The person drawing these(surveyors helper), are not assigning a coordinate system. He will start with a blank drawing and insert the ground points from the GPS. But if I assign our coordinate system(State Plane North Zone...) in Civil, isn't that Grid? 

So my question, do I assign a coordinate system to my drawing before inserting points? Do I insert the Grid or Ground points? I will want a final ground drawing to match the embankment drawings. But my GIS is all in Grid, so my final project I want to be in Grid. 

Thanks, 

Rich

[sboon]

Within the ACad environment all coordinates and distances are cartesian values (same as ground coordinates)  Everything that you draw is assumed to be ground based.  If you set a grid coordinate system, turn on the transformation tab and create an imort/export format that uses grid northing and easting values then you can import grid based survey data and have it scaled and translated to ground.

Note - you can also do everything above but leave the transformation tab off.  In that case grid coordinates are assumed to be the same as the local ground coordinates.

One other reason to set your coordinate system is if you plan to import data from other sources.  GIS, Lidar and shapefiles are all typically grid based coordinates so you need to tell the software what system the drawing is in.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

[antoniovinci]

I concur with Steve: said in simpler words, for Autocad the Earth is flat.

[sboon]

The earth is flat - and the universe is a cube.

[neilyj666]

The being flat would explain why get so many drawings with elevations of zero

[riverdeer]

I will have to look into the transformation. I always did it manaully later in the csv file by using the scale factor. 

So if this was your setup, would you assign it into a Grid coordinate? Or just draw it with no coordinate system(ground)? 

When I am using my GPS, I do all my work in Ground. But yes, all my GIS, LiDar, and photos are in Grid. So if I want to import/export into those, it's nice to have it with the same coordinate system. 

Thanks, Rich

[Pointdump]

Rich,

Here's some good videos on the subject of Coordinate Transformations by the late Richard "Sinc" Sincovec:
http://www.quuxsoft.com/Video_Tutorials.aspx

Dave

[riverdeer]

I thought I understood it but now more confused. When I assign the coordinate system I thought I was saying I was in Grid. But after watching this first video about transforming Project Coordinates, he is assigning a coordinate then telling CAD to giving him Grid. 

So the attached JPG, is that Grid or Ground? Here the scale factor from Grid to Ground is 1.000130347 and Ground to Grid is .99986967. 

The video was great help of what to do. But just confused on after I say I'm in ND State Plane North... if I'm in Grid or Ground. 

Sorry for the confusion. 

Rich

[sboon]

Coordinates within the ACad drawing environment are assumed to be ground.  If you set the Units and Zone tab to "No Datum, No Projection" then the software ignores this issue completely.  Grid and ground coordinates will be the same, and you can tell people that your drawing is using any coordinate system that you want.  The problem here is that you cannot use the Map tools to import data from outside sources and you cannot translate or scale survey data during the import/export process.

The second option is to set the Units and Zone tab to the appropriate system for your locale, but leave the Transformation tab turned off.  In this case ground and grid coordinates will be the same, and the Map tools will work correctly.  You can still tell people that your coordinates are grid or ground - whatever the surveyor supplied you with.  I use this option most of the time.

Third choice is to use the Transformation tab to apply a scale factor and optional transformation.  The scale factor you enter is ground -> grid.  If your import/export format specifies that you're using grid northing and easting then your survey points will be adjusted and your ground coordinates will be different than your grid values.  Please note however that this transformation only applies to survey points.  LandXML files and data transferred through add on tools like Trimble Link will not be adjusted.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

[rl_jackson]

I believe he was just demonstrating different ways to get the answer based on what was provided. In that particular case he had ground, and wanted grid.

However, if you have Grid coordinates. I would use those, and apply the local (published or calculated) scale factor for your site so that C3D scales your data for you to ground. (i.e. Let the software compute the ground coordinates on import)

A word of caution, you really should not use transforms on large sites over miles as the scale factor changes in a North South direction. In those instances you should really think about using other transform methods (low distortion) or keep everything on Grid (no scale). and export only Grid data.

[Pointdump]

Rich,

Attached, here is some reading material to go along with the videos.

Dave

[Crudkin]

I have a civil3D surface generated from a Lidar point cloud.  This Lidar data was defined using GRID coordinates.  However, our client has requested that all designs be done using GROUND coordinates.  

As Steve mentioned in an earlier post, the autocad environment assumes a GROUND coordinate system.  So, how do I use GRID-based Lidar points to produce a GROUND-based design?  Is there a tool within Civil3D to convert the Lidar surface to a Ground-based surface?

Thanks,

Caleb