This method is used to get the URL of an S-Drive Attachment's Thumbnail File.

String getThubmnailURL(String parentId, String fileObjectId, Long timeValue)

parentId: Id of the parent object. You can use 15-character id or 18-character id.
fileObjectId: Id of the attachment (file) object. This can be retrieved using an SOQL query.
timeValue: Expiration time of the link in seconds.
Return Value: The method will return the URL of the S-Drive attachment's thumbnail.

If you would like to get thumbnail URL of an old version of a file, you should add id of an old version file into fileoObjectIds list.