As someone who enjoyed playing the computer games, but not played the tabletop yet, these are my recommendations based on how I followed it.

First start with the Horus Heresy books; Horus Rising, False Gods etc. Then start Galaxy In Flames then The Flight of Eisenstein. After the first 2 books you would have what I believe is a reasonable grasp of the 40k universe with regards to the Imperium of Man v/s Chaos and why there are Traitor Legions within. You could then move on to discovering the other xenos aka Orks, Eldar etc. 

The books are a pretty easy read, but don't let that put anyone off as they are quite politically focused intertwined with some good narrative. 

However the downside, in the humblest of my opinions, is that I am starting to find the "Imperium of Man" is a bad organization. Especially with Horus being a Warmaster or have I read them wrong even before Heresy sets in. Of course Loken and his comrades are still good guys :). Maybe a spoiler there sorry :(

So go with Horus Heresy 1st 1-4 books if you're like me and only dabbled in the periphery of W40k.

What is the best place to start Warhammer 40k?
How many cameras apart from the iPhone have a gyroscope for orientation?

Am I right to assume that there is a standard way to “tag” an image with the direction the camera was pointing in, as well as the GPS position?

Do any cameras have positional tracking better then a GPS?

I am thinking about a method to join photos when the subject does not have enough “random” detail for the current software.
