Best Way to Import a Surface

[sarah_karan]

In the projects I am currently working on I am going to spatial data download and downloading the DEM files for my area. I then go to toolspace and insert my DEMs through the DEM files folder. I have found though that it slows my drawing down tremendously and even causes it to crash at times. It honestly makes the drawing almost unusable at times- I use the boundary feature and data clip it to as small as possible but even then it causes so many issues. I looked into downloading the contour data as a shapefile from nationalmap.gov but have found that the information is not near as accurate. Just wanted to see what others are doing and what the best way to import surfaces is? 

[cwr-pae]

I typically use a 3rd party program to trim dems down. Global Mapper is the one we purchased, but i understand there are free ones available. I also create an empty surface and then add the dem data as opposed to creating one from a dem. Though I'm not sure that has much effect on speed.

[sarah_karan]

Thanks for the advice about trimming outside of C3D, that could help. I believe that is also how I insert the DEMs as I right-click on Surfaces and click create Surface.

[Pointdump]

Hi Sarah,
DEM's are a derivitive product, once removed from the original LiDAR data.
LAS or LAZ files can either be run through ReCap or you can use DotSoft's excellent free >>>Lidar Tools<<<.
As you import a ReCap RCS file into Civil 3D, there is a step which allows you to decimate the points to any spacing, e.g., 1mm, 1 meter, etc. That way you can adjust the surface size to make sure it's under 2 million points, and you won't create the dreaded MMS file which is a death sentence for a surface.
Dave