The picture shows the situation between sunrise and noon: the projection of the sun onto the xy plane lies somewhere on a line through the origin, and phi is the angle this line makes with the positive y-axis.

For times between noon and sunset, the projection of the sun onto the xy plane still lies on the same line, but is now on the other side of the origin. According to the convention given by ӜЯℱӁℒᚹ above, the azimuth of the sun has changed by 180 degrees. But the azimuth argument in the kata still refers to the azimuth the sun had before noon, not the azimuth it has now.

The only thing that really needs to be changed is the specification of azimuth: instead of saying

azimuth : Azimuth ϕ of the sun in radians.

it should say

azimuth : Azimuth ϕ of the sun at sunrise, in radians.

At the same time, the input arg phi means the azimuth at sunrise

What is implicating this?

I'm still not sure, what is the problem.

As much as I understand, geoffp means that after passing through the overhead point (zenith), actual azimuth of the Sun changes by 180 degrees. For example, if the azimuth is 45deg before the noon, it becomes 225 deg after the noon. At the same time, the input arg phi means the azimuth at sunrise, and not at current clock.

Hey, I worked on this kata around 10 months ago, so I've almost forgot all the particularities associated with this, can you please ellaborate a bit more?

From what I can read from the test cases and description, you must've mean that the convention used for azimuth should be specified, and I think here, it is the angle of projected vector of position vector of sun on x-y plane, measured from the positive y axis along the anti-clockwise direction(right hand rule). So is this the specification that I need to put, or I've no idea what is wrong?

Nice kata, though a bit too easy for 3kyu.

There is an error in the description: azimuth is not the azimuth of the sun, but the azimuth of the point where the sun rises. After midday, the actual azimuth of the sun will differ from azimuth by 180 degrees. The picture shows the situation correctly, but the text above it is wrong. (I took the text at face value, and spent quite a while figuring out what I was doing wrong.)

Awesome new description. 10x better than the previous one.
Thank you!

Approved.

This kata is great and I want to thank the author for the idea, and doooom and XRFXLP for bringing it to a good shape.

So awesome!

Nope, thanks for the efforts. :D

Sorry about that.But when I made that comment, I'd no edit privilege. So, all I can do is say someone who has the same to do so.

mmm

edge and point should block the light.
added random tests to 1000.

Johan, can you cast your difficulty vote on the kata? hopefully this time it will be able to collect enough votes so the suggested rank will reflect the difficulty somewhat better.

Or have you already?