boost serialize - not such a good idea!

I'm a big fan of the boost libraries for C++. Mostly, they are a huge productivity gain - things like regex, function and bind can reduce the work involved in a complex program by half or more. So when I needed to pickle a very large (gigabytes) and complex data structure between restarts, boost was the obvious place to look.

Boost serialize certainly looked like the answer. Just add a few lines to each class saying what you what to save and restore, then with a single function call, you can pickle the whole structure and later reload it. It takes care of loops, diamonds and all the other things that happen in real-life data structures. And if you don't like the default way of saving something, it's easy to write your own. How good can it get!?

Well, that's the theory, and it could have been the practice too. But it isn't. For some reason known only to themselves, serialize's authors decided that the C++ inheritance mechanism wasn't for them. They invented their own completely parallel mechanism for dealing with polymorphism and subclasses. The effect is that trying to save my structure results in an exception thrown from somewhere in an enormous depth of function calls. I persevered, and tracked down what was happening. For some reason - and it's just impossible to plough through all the code and figure out the details - it silently ignores some of the calls to the subclass registration process. After several days of trying to figure out the details - on a live application because that's the only place the data can be collected - I have finally given up. I'll live without this capability in my program.

Unfortunately this is a common problem with boost. It seems to be de rigeur to invent new ways of doing things even though they are more complex and don't work especially well. The build system is another case in point - instead of using make, known and hated by generations of programmers, they invented their own, bjam, which is unknown and incomprehensible. If it works for you, great. If not, forget it.

I'll carry on using boost, but you do have to be selective. Unfortunately.

More thoughts on Boost here.

Divisumma, the Star!

A few weeks ago I got an email fom someone saying, in essence, "Can I come round and get some pictures of your Divisumma please?"

I was surprised, especially when I discovered he was coming from Detroit - I would have thought there would be more around than that. He is making a video about architecture for Yale, and had been specifically asked to include some footage of the Divisumma. He'd evidently had trouble finding one in the US but - thanks to this blog - he found mine.

He came by today and spent half an hour or so in the sunshine, shooting very close-up footage of the keyboard and the case. And, when he's finished putting it together, Divisumma will be a movie star!

Halfway to Upside Down

When I started this blog it was with the intention of writing regularly about aerobatics - hence the title. But you know how things are... I got involved with learning to fly the heli, which dramatically reduced the amount of acro I fly.

But today I flew the Pitts, and I took my camera with me. It's hard to take pictures of aerobatics while flying solo, I can tell you - trying to fly a tricky manouver left-handed while holding the camera with the right and trying to get it to focus on the right thing.

I did however manage to get a nice picture of a knife-edge. That's when you hold the airplane in a 90 degree bank, which means that the wings aren't providing any lift. So the only way to maintain altitude is to hold a very steep fuselage angle and let the fuselage provide the lift, which means LOTS of top rudder - in the Pitts S2C, full top rudder. Of course the drag is huge, so you slowly lose airspeed and eventually you will fall out of the sky. But you have long enough to take a nice pic, like this one.

Full size photo, and others from the same flight, here.

BBC News RIP

For years I've got my daily news fix from the BBC news site. It was well arranged and would give instant access to the top world stories and, when I was feeling nostalgic for good ol' blighty, the UK. There were always a few interesting tidbits. And it was free, too.

Then, a few months back, some genius in marketing (I presume) decided that the page needed a New Look. Ever since, I just can't find any news on it. It's not just me, I have a colleague (Iranian) who has exactly the same feeling. Somehow, they just messed it up. I guess all the same news is still there, but it has lost its interest and salience.

Today I signed up for a subscription to The Times (the London one). Goodbye BBC news. I'm sorry to have lost a friend.

Flying under the Golden Gate Bridge

I did it! On Sunday we flew the helicopter under the Golden Gate Bridge. It was pretty exciting. The picture shows us just approaching the bridge from the east. We're at 100 feet, about half the height of the deck.

The sight-seeing operators do this all the time. I was astounded when I first saw the red Jetranger that does these flights around the city zoom under the bridge. It's quite legal. There's a special exemption to the regulations that allows helicopters to fly pretty much anywhere without the distance requirements that apply to airplanes. (Take a look at FAR 91.119 if you're interested).

I'd discussed it with my instructor a few months ago. The plan was to fly through the SFO Class B airspace up to the city, under the bridge, then back again by the same route. Unfortunately though, since the incident earlier this year, SFO Tower is being much more cautious about Class B transitions. During the busy part of the day, they are generally not available. And indeed that's what San Carlos tower told us . Our second plan was to cross the hills at route 92 over to the coast, and go round the Class B. Although it was cloudy, there was plenty of room under the clouds to do this.

But then San Carlos handed us off to Norcal Approach, who cleared us through the Class B at 3500 feet. I've been given this transition before and it works well. Sometimes you have to ask for it, a bit like Special VFR. So we climbed before we got to the clouds, flying over the undercast and also the SFO departure corridor. It was very pretty, the airport and the city were both visible through gaps in the clouds, although I didn't manage to get a decent picture.

Then a very rapid decent once we were past the Class B surface zone, down to 700 feet and ready for the big adventure. We went over the south end of the bridge, slowed right down in a left descending turn, and at a stately 40 knots or so passed under the bridge at 100 feet. It was over all too quickly.

Although it's perfectly legal, we were both a bit nervous that people might react badly, so we climbed well away from the bridge, back over the south end, and then across the Bay to Oakland for the transition back south.

More pictures on Flickr.

Audrey Hepburn and the Eiffel Tower - twice!

There are two movies that feature both Audrey Hepburn and the Eiffel Tower (well, I suppose there could be more). One is well known and you will find it by googling those two subjects - Funny Face, one of her hallmark movies. It's a great movie, which we saw at the Stanford Theater last night. (One of the really nice things about living near Palo Alto is this movie theater, lovingly and expensively restored and specializing in classic movies, mostly pre-1960).

By coincidence, we had watched the other one the previous night at home. Any guesses? It's the Lavender Hill Mob, one of the greatest of the British Ealing comedies, from 1951. The main characters are Alec Guiness and Stanley Holloway, with other classic stars from the time like Sid James and Sidney Tafler. The Eiffel Tower has a central role in the plot, including a fantastic scene where the two heroes run down the emergency staircase. And Audrey Hepburn? In 1951 she was still an unknown. She has a tiny walk-on part at the beginning. You wouldn't recognize her unless you were looking. It was only when the closing credits rolled by that I saw her name.

Going back to Funny Face, there are some wonderful period-piece scenes. For avaiation fans, the scene of the TWA Constellation taking off is enough to make the whole film worthwhile. Then they land at Orly, where on short final they fly over Notre Dame and the Champs Elysees. Funny, this never happens when I go to Orly.


Another great detail is the Isetta, a 1950s "bubble car". It's a weird little thing, with a single door which is also the front of the car. For the movie they gave it a funny pweep-pweep horn, which the real thing didn't have.

o hisashiburi desu nee!

Just looked at my blog and realised it's months since I wrote anything. (The title is Japanese for "it's been a long time, hasn't it!"). A lot has happened in that time. I got a wonderful hexapod (six-legged) robot from Micromagic Systems, with lots of intentions to write software to do all sorts of clever things. I figured out the math for how to make it go where I want to, which involved re-learning a lot of things that I never really learned in the first place, like matrix math. I got a lot of code written, too.

But then real life intervened - I gave myself a new work programming assignment, and I really can't do two big, new pieces of software at the same time. So I haven't touched that in several months.

The maze solver got put to one side when the hexapod showed up. I'd realised that you just can't track the rotation angle of the 3pi by monitoring the motors. So I had to make the compromise of requiring mazes to always have 90 degree angles in them. I started to make the necessary software changes when, again, real life got in the way.

Then we went travelling, first to Japan where we had the immense good fortune to attend a friend's traditional Japanese wedding, then to France on holiday.

I'm still flying - I've got (at least somewhat) back in the groove with the Pitts, and I fly the heli once a month or so. My precision autos are getting better, and there are times when I think that autos are the most fun you can have with or even without your clothes on. (Maybe that's just a sign of advancing age though!). I've also started work on my CPL-ASEL (commercial license, that lets me get paid for flying, should I find anyone willing to do so), though that hasn't gone very far for all the above reasons.

The Divisumma still sits on the corner of my desk, with its very attentive operator. It still seems to be working.

And that's about it, four months of my life summarised in a couple of paragraphs. Hope to get time to keep this blog a bit more up to date in the next few months.