To learn a bit about panels I’ve created a script that measures the distance of selected objects and the 3D cursor (this depends on what is selected).
To be honest I didn’t search if something like this already exists (for 2.5 that is, I know of the 2.4x scripts  and ).
As already mentioned I did this to learn a bit about the panel API stuff in 2.5.
This script displays in OBJECT MODE:
The distance of the 3D cursor to the origin of the 3D space (if NOTHING is selected).
The distance of the 3D cursor to the center of an object (if exactly ONE object is selected).
The distance between 2 object centers (if exactly TWO objects are selected).
The surface area of any selected mesh object.
Display in EDIT MODE (Local and Global space supported):
The distance of the 3D cursor to the origin (in Local space it is the object center instead).
The distance of the 3D cursor to a selected vertex.
The distance between 2 selected vertices.
The surface area of any selected face.
It’s very helpful to use one or two “Empty” objects with
“Snap during transform” enabled for fast measurement.
Get units to work with the script (Right now only raw blender units are used, not metric/imperial stuff)
Lamps and other objects are not show with their correct icon … dunno if this is a good idea?
Icon for absolute origin (is there one?)
Measurements in Edit Mode have to be updated manually. Not much I can do here, this is a problem that is in Blender quite some time now.
IMPORTANT NOTE! gitorious.org has been discontinued. There is (was?) still a read-only mirror of the former gitorious.org site available - which doesn’t seem to work anymore?
Anyway, the last version is also available in the “Blender Add-ons Contrib” (BAC) Blender code repository:
Yes, that’s how the value got displayed in the very fist version of the script.
Unfortunately one can’t copy a lable text into the clipboard (at least I couldn’t find a way).
So one can measure something, copy the value and use it somewhere else.
(That was one of the reasons why I asked about the FloatProperty stuff on IRC.)
I’ll have a look at the grease pencil stuff. Looks like a good idea.
A non-permanent (i.e. never saved) solution for this would be better in the long run though.
OpenGL drawing (and the temporary FloatProperty for the situation above) would be helpful - but I can manage until then
Thanks for the link, I’ve added this to the original post.
I’ve planned to add various measurements like this to the script, but I’m still working out the details.
Couldn’t agree more, but until somthing like this is integrated into the script may take some time.