Modified interactor style: display camera parameters

[VictorLamoine]

This is a more user friendly way to display camera info when the user presses "C" in the viewer. It also changes the way .cam files are written when pressing "J".

Example of new output :

Clipping plane: [near, far] 0.605189, 5.31035
Focal point: [x,y,z]    0, 0, 0
Position: [x,y,z]   -0.77742, 0.395603, -2.23865
View (see doc) [x,y,z]  0.11999, -0.969652, -0.213021
Camera view angle:  0.523599 rad
Window size: [x,y]  960, 540
Window position: [x,y]  903, 249

[taketwo]

It also changes the way .cam files are written when pressing "J"

Well if you change the format of '.cam' files then you have to modify the code that loads '.cam' files as well (which you did not). But apart from that, I think it is not a good idea to change the format. For example, in my personal projects I have code that relies on the existing format of the file, so your change would break it.

Summarizing, I like the update for on-screen output, but the '.cam' format should stay the same.

[VictorLamoine]

Agreed, there is no need to modify the way PCL writes '.cam' files.
The pull request now only changes the way PCL show camera parameters.

[taketwo]

Also what do you think about the following:

• Radians vs. degrees: perhaps it's easier for a human to parse the latter;
• Put rad (or deg if we decide to switch to it) inside [] in front of the number (just like other [x,y,z] stuff);
• Is (see doc) really helpful? Which doc?

[VictorLamoine]

I changed the display to degrees. It's easier to parse this way. Moreover the field of view is rarely given in radians.

I changed "view (see doc)" to "view up" to match the name in the documentation:
http://docs.pointclouds.org/1.7.1/classpcl_1_1visualization_1_1_p_c_l_visualizer.html#ab2039927ec8f5a9771202f269987ec72

Is it ok this way ?

[taketwo]

Great! Please do the last two things to polish the contribution:

• Change tabs to spaces;
• Squash the commits in a single one so we do not pollute the history. (After squashing locally just git push --force and this pull request will be automatically updated).

[VictorLamoine]

Done. Thank you for the detailed instructions !

[taketwo]

Looks perfect now, thanks for the contribution!