Not sure if it helps, but try to edit the "Path" and the "Exec" line in your .desktop file like this:

Path=/home/derek/SweetHome3D-6.4.2
Exec="/home/derek/SweetHome3D-6.4.2/SweetHome3D" %U

And then save this .desktop file in

"/home/derek/.local/share/applications"

SweetHome3D will now appear in your applications.
You're right, starting from the terminal is not an acceptable option. But you could even start a software from the terminal with a .desktop with the corect exec line.