Monthly Archives: February 2013

View Frustum

I came down with a cold late last night so I have been sitting at the computer for 8 hours today working on frustrum-related programming.  Some of the time was spent on our modelling tool called Makeship.  Some of the time was used to develop a spreadsheet which can be used to find an inner polygon given a three-dimensional polygon.  But most of the time was trying to figure out how to take the 8 vertices that I have yet to calculate and build a projection matrix.


Presumably it can be done since the matrix can store the information we need – but the math is apparently very complicated so we will have to accomplish it through multiple concatenations.


Another approach was to take the 6 planes that are described by the 8 vertices but that was shot down too.  I took an excerpt from this article:

… there’s a reason the Digital/VFX industry hasn’t done this already =)

Live Broadcasting

Compared Ustream to Livestream and went with Ustream.  You can see the channel feed on the left above the archived content.  If we aren’t “live” you have access to previously recorded video.  Much easier than what I tried before!  I will basically leave it up and running 24/7 but send notifications through the channel of planned sessions and I will record those planned sessions.

The cameras I have are horrible.  The ones I bought on eBay have a 12 mm lens!  According to this calculator that means I am only getting a field of view (FOV) of 28 degrees!  So their claim that they are 60 degrees is just bogus.


In researching a good replacement I ended up buying the Genius F100.  It boasts a 120 degree field of view and 2 MP per frame at 30 FPS (required for HD video).  Should get it in a few days.  Another bonus is that it has a stereo microphone built in!


Port Interior Panelling

Kids helped me rough up the HDF with sandpaper. Then they helped me paint! It turned out nice and they didn’t make a mess.


My wife helped me find the material for creating a stencil and then even helped cut the plastic for me! This stencil is used for the screw locations since it is critical that I don’t drive a screw in the wrong spot or there goes an HD monitor!



Visibility on Venus

Took the mg/m³ values and tried to figure out how they affected visibility.  I came up with a solid source that stated 0.1 mg/m³ was 7.5 km in dry air (Venus has 0% RH).


The plot looks linear but if we extrapolate to 0.001 mg/m³ it would be 750 km in a layer that is purportedly “haze” which is, by definition, 5 km or less. They I ran across this graph that used the Extinction Coefficient instead of density.


Which led me to Koschmieder’s Relationship: If k(e) is σ then V = 3/σ or 3 km at 60 km… seems a little high!  Is that because water droplets are so much larger?  If k(e) is in km then there is no further conversion, right?

Stationary Orbit Above Venus Clouds

I performed an interesting exercise over lunch today.  Calculating the geostationary orbit above a floating mine in the clouds of Venus at 50 km AGL.  I used this tool online.

2-6-2013 1-11-41 PM

Satellite at altitude 142900.264 km

630942.04 seconds in a sidereal day, 60.27m/s (216.96km/h) base velocity

actual g: 8.869399842321876m/s2

324835411994007.75=GM (μ), 0.01 g (orbit)

Orbital velocity: 1476.75 m/s (5316.32 km/h)

Orbital length 633750 seconds (176 hr 2 min 30 sec)

Max visible latitude: 88 degrees.9260.2km coverage radius
0.48s/0.5s min/max one-way radio transit time.

That is considerably lower than the SOI for Venus (616,000 km) and Venus has no moons… much better than I can say for geostationary orbit above a ground position (1,536,647 km) with it’s super slow retrograde rotation (243 days).  But still, that is pretty far away!

I will leave you with a cloud density profile that I found online.