A surface has a limit to the number of points it can contain before caching its definition to an external file. The only way to prevent this is to reduce the amount of data in the surface definition. If this is not an option, the cache file will be created in the same folder where the drawing file has been saved. This file must remain in the folder with the drawing file for the surface definition to remain in the drawing. If the cache file is deleted, moved, or renamed, the surface will no longer appear in the Prospector or function in the drawing. What will remain in the drawing will be a proxy entity.The cache file will bear the name of the drawing file along with its AutoCAD object handle ( <drawing_name>_<surface object handle> ). For grid surfaces, the limit for the number of points is about 1 million, and the file extension of the cache file will be .grs. For TIN surfaces, the limit is about 2 million, and the file extension of the cache file will be .mms. There are several options for working with large surfaces depending on the situation:
- Data Clip Boundaries
- As discussed earlier, a data clip boundary is a type of boundary that can be added before any elevation data is added. This is the best option to use if you have information covering a large geographic area but are working only in a smaller area.
- Cropped Surface
- The Create Cropped Surface command can be found in the contextual tab of your surface, hidden in the Surface Tools panel flyout. This command will break off a piece of a surface model and allow you to send the smaller piece to a new drawing. This is a fast way to create a new drawing containing the desired surface data. The major disadvantage to the cropped surface tool is that there is no connection between the original surface and its spawn. In other words, if the original surface is changed, the new surface will not be affected.
- Data Shortcuts
- The best of both worlds, data shortcuts allow you to work in a new file but remain connected to the surface’s source data. Another major advantage of using data shortcuts is that multiple users can access the surface data without duplicating it.
Here are some other hints that will be helpful in increasing performance when working with large surfaces:
- Turn on the Level Of Detail option in the Views panel of the View tab.
- Do not use the Rebuild-Automatic option.
- Turn off the selection preview on the Selection tab of the Options dialog.
- Clear the Show Tooltips option in the Surface Properties dialog.