This is a mod that allows you to see through some objects, such as walls, trees, or buildings. The more you get closer to these objects, the more transparent they become. 

The default setting for this mod is a transparency of 0.5, meaning that you can only see half the distance between you and the object you are looking at. This can be adjusted to a maximum of 1.0 and a minimum of 0. The maximum distance is an integer number of pixels, and the minimum transparency is a decimal number between 0 and 1.

You can also set the minimum and maximum distance in the config file that is created after running SDV with this mod installed.