Understanding Great Circle Arcs Intersection Algorithm

The following material is the result of my attempt to understand the nice example from Jason Davies. I was puzzled about the origin of the algorithm used to find the intersection of two great circle arcs. Google helped and I discovered Roger Stafford’s post in Matlab newsgroup and the relevant Python’s implementation in the Spherical Geometry Toolkit. The algorithm You have two great circle arcs on a sphere, $a$ from point $\mathbf{a_0}$ to $\mathbf{a_1}$, and $b$ from $\mathbf{b_0}$ to $\mathbf{b_1}$, whose coordinates are expressed as longitude $\theta$ (positive going East of Greenwich) and latitude $\phi$ (positive going North).

Failing to be recruited...

This post title to be frank should have been “Impressions about the selection process of a big Internet company (and my failure to go to the next steps after initial engagement),” but that is obviously too long. So I only kept the failure part with the aim to bring home some lessons from it ! 😏 Chronology, more or less It all started with an email at the end of July 2014 from the company’s recruiter, let’s call her Alice.

on revising

Lately I found myself involved into writing. And I have been often cought into the vicious cycle of revising my (or other’s) text without really understanding how to do it properly and when to stop. I want to summarize some of the advise I found on the web. I put it here for me to find it again and share. Let’s first paraphrase the famous grook from Piet Hein: THE ROAD TO WRITING?

Automatically extracting bomb drops from the Blitz Bomb Census maps

I just finished Blackout by Connie Willis and I was wondering where she did get all the exact times when the air raids of The Blitz were happening. I am curious because I was thinking that a timeline map would give a visual effect of the huge destruction and hard times the Londoners had to go through…so I googled for it and found the following: a nice research blog which uses the Blitz Bomb Census from The National Archivesa blog entry from the Guardian about the first day - and data - of the Blitz over London.

wiki of the future?

Last weekend I have been watching, reading and playing around with Ward Cunningham's Smallest Federated Wiki. As usual he is a great designer and aims to simple, effective, understandable and useful tools! I particularly like the plugins idea (not new of course) and how easy it seems to be to add new ones, like support for MathJax:
Get inspired you too!


I found and liked a very good summary of the ‘Maxwell Equations of software’ motto from Alan Kay in this post from Michael Nielsen.

It is nice also because it has running code inspired by all the gurus and books I like: Alan Kay, Peter Norvig, John McCarthy, SICP, Paul Graham.

syntax highlight

The following example shows how to syntax highligh some snippet of code in a very minimalistic way. I used it by symlinking to a file in the version control repo and name it in as the argument of $(‘#code-area’).load() and here it is:

code higlighted with minimal javascript

Metacircular code highlighting The following code is an highlighted version of this very page using

Git and RSA identities

Here is the solution I found to be able to use git with a different RSA identity than the rsa_id default one. My repo on github is logback-android and my user account is espinielli. I did generate an SSH key as per github help and named it github_rsa: $ ssh-keygen -t rsa -C “” -f github_rsa I then added the following section in ~/.ssh/config

github for espinielli

Host github

LaTeX on Blogger again

My previous post about LaTeX  on Blogger reported that the solution described there did not work anymore...
Now I found a new solution based on mathjax.

So let's try it straight away with inline math, like the great equation \(e^{-2\pi}\), and with displayed math like the following:
\[ \left [ - \frac{\hbar^2}{2 m} \frac{\partial^2}{\partial x^2} + V \right ] \Psi
= i \hbar \frac{\partial}{\partial t} \Psi \]

(What was) Croquet is maybe still alive

It seems there is still some hope to see Croquet (or, OpenCobalt which took off from where Croquet stopped) alive and based on latest Squeak and more importantly using Cog VM.

Matthew Fulmer reports it here.

The potentials are magical as explained by Howard Stearns.