February 2020 Summary


  • Worked on Project History and Archiving
  • Completed 2019 federal tax returns
  • Assembled “Down the Rabbit Hole” as an Open Movie
  • Learned how to work with Kdenlive “Archived Projects”
  • Migrated most content from lunatics-unversioned
  • Migrated sound effects library and cleared licenses
Feb 22, 2020 at 4:00 PM

Sunlight Armature Rig

I am creating a sunlight control armature. This rig essentially calculates the correct position for the sun in the sky, based on information about the location on Earth, time of year, and time of day:

  • The root shows the ground-north direction for the set.
  • The equatorial-north is set to the site latitude (at the equator, it points directly along the ground north vector, at the north pole it would point straight up, perpendicular to ground-north).
  • With the local-time HourAngle vector set to “noon”, the ToSun vector is set to the “solar declination”, which changes by season. It’s -23.5 degrees at the Winter solstice, 0 degrees at the equinoxes, and 23.5 degrees at the Summer solstice. Other times can be looked up on an ephemeris, or we can just approximate (it basically follows a sine wave pattern over the year, ranging between the extremes at the solstices).
  • The hour-angle vector for the Sun is then set based on the local time (that is, the time based on noon being when the Sun is actually at its highest point — this may differ by as much as a half-hour from the “civil time”, depending on where you are in the time zone).

Right now, these have to be manually set. I probably could write a driver program to input more familiar values: latitude, date, and local time, but I’m not sure if it’s really necessary.

The rig in the picture is set to about 7AM for Baikonur in April, which is when the pilot episode is set.

The reason I want this rig, other than just getting the lighting angle right, is that I plan to animate it for a “timelapse” effect during the “Soyuz Rollout” sequence. Actually putting a rocket on the launch pad takes a good part of a day, and our script calls for condensing that into two “timelapse” shots, both of which will use this rig for the changing daylight.

The next part in the process is to attach the sun lamp, shadowcaster-lamp, and hemi fill (for scattered light) to the rig. I also need to create some kind of “airmass” control to deal with the light changing near sunrise and sunset due to passing through the thicker atmosphere and clouds. I haven’t quite figured out how to do that, but essentially it will need to redden the light.

There’s also going to be a “Sky” hemi which will gradually change color during the day, but it will probably remain straight overhead, representing the broadly scattered light from the blue sky.

And then we’ll need our existing “cloud deck” animation system to cast cloud shadows and show the clouds evolving and moving in the sky (the current system uses a procedural “cloud” texture, with the Z axis changing the clouds, while X and Y move them across the sky dome).

It’s nice to finally put my astronomy knowledge to work on this project!

Also nice to have finished the beginning-of-year administration work and be back to production work.

I know it’s probably not very clear yet what this will look like, but don’t worry, I’ll be posting more updates soon!