grid surface shift?

[Anonymous]

Recently a client gave us a large adf file containing grid elevation data. The data are mean elevations per grid cell, and grid cells are defined by their southwestern corner. 

If we use the sdf function in MAP3d the grid is shown at the correct location.

When we try to make a surface from this data (create surface from dem) in CIVIL3d the result is a surface that has a correct southern and western border, but a northern and eastern border that is offset by the size of 1 gridcell.

We believe this to be the result of two issues:

1- CIVIL does not seem to interpret a grid surface as a surface made up from level areas (the grid cells) but rather as point elevation data with the points in a grid.

2- CIVIL uses the x,y coordinates from the adf file, wich in our case is a corner of the grid cell, where if need be we would prefer using the centerpoint.

My question here is:

Are we correct in our analysis, and is there a way to do this differently so that we can use the data better?

We tried moving the surface after creation (with the autocad move command) but that led to a crash. 

Cheers

Dale Rudrum

[ericcollins6932]

To start, it would depend on what you mean by - large number of points. Are we talking a few thousand or a few million?

My brute-force solution would be to bulk shift all the xy by the amount to shift the coordinates from grid corner to grid center and then import. Either while importing or bulk shift after loading (assuming these are being imported as C3D points) or by another third party solution (if being loaded as a point file).

You are correct, C3D takes pts as TIN nodes and creates its surfaces that way.

[Anonymous]

Hi Eric

Thanks for your reply.
Unfortunately adf is an Esri file format with which we cannot do anything besides what CIVIL can do. CIVIL does not import the points, but retains a link to the adf file as the source of surface data. We suspect that is also why shifting the entire surface does not work.
Large files in our case means tens of millions of points.

Met vriendelijke groet
Dale Rudrum
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[ericcollins6932]

Hey Dale,

Excuse my confusion - is your data source .sdf or .adf?

[sboon]

If it is adf then this link may be helpful.  I'm curious about exactly how you're getting this data into your surface definition.  Are you using the Add point file option or something else?  If it is a point file then it should be possible to set up a transformation in the drawing settings and then load the file as grid data.

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

[Anonymous]

For the surface we use the function.
adf is one of the fileformats that can be selected for this function.

Adf's can also be viewed using map3d functionality:
In Data Connect window choose

and find the adf
This gives a view of the data simmilar to elevation banding in a surface but has none of the other surface functionalities.

When using both methods in one drawing the results differ as I described in my first mail.