How to get the center of a viewport with AutoLISP

The free viewportcenter.lsp has been updated with more functionalities.

This app shows the coordinates for the center of the current viewport on command line.

If command is run within a viewport in model space it can be run transparently for example like this using 'vpc
   Command: LINE
   Specify first point: 'vpc

If command is in paper space it will ask to select viewport and the point will be available as last used point and can be used with @ like this:
   Command: LINE
   Specify first point: @