An sdts file extension is related to the Spatial Data Transfer Standard format.
SDTS file extension - Spatial Data Transfer Standard data
What is sdts file? How to open sdts files?
File type specification:
The sdts file extension is associated with the Spatial Data Transfer Standard.
Spatial Data Transfer Standard, or SDTS, is a robust way of transferring earth-referenced spatial data between dissimilar computer systems with the potential for no information loss. (10m and 30m 7.5' DEM)
This sdts file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.