Category: Geekery

Nav data update

I’m testing a new update script for my navaid.com waypoint database. The old update scripts were written for when I was running on MySQL, and I’ve switched to PostGIS to support the new iPhone version of the CoPilot flight planning program. One of the salient features of the new iPhone version is that it attempts to be smart about downloading waypoints as you need them. One of the ways it does that is by asking my server for all the points in a particular area that have changed since a given date. The app keeps track of all the “areas” it has seen, and when the last time it was updated, and asks for an update of those areas at certain intervals. But that means I have to keep track of when a point was last updated. It also means that I need to keep track of what “area” a point is in. For the areas, I use a pseudo-quadtree where I allow only 500 points in an “area”, and when it gets more than that I split the cell into four sub-cells and mark the original cell as “superseded”. The new sub-cells have a “supersedes” value, so if the app asks for an area X, and area X has been split, I can say “X has been superseded, and here are the area ids A, B, C, and D that supersede it.”

But all this means that my new update scripts have to get the new data for a waypoint, figure out which old waypoint it was equivalent to (even if the waypoint has been resurveyed and is at a slightly different location and/or it has changed id), and only save the point anew if something significant has changed. Oh, and if the new data is missing information that the old data has, try to be smart about keeping the old data – for instance, George Plews’ Airports In Canada web site has data for airports in Canada that I can’t get any other way, but it’s also got data for airports that either were in the DAFIF data or are in the FAA data, and those two data sources often have much more information about runways and communications frequencies that Plews doesn’t have. So I want his latest data, but I don’t want to lose the other stuff that he doesn’t.

One of the things I do to match up the old with the new data is look with a bit of geographic “slop” – in the case where the ID matches I look within 0.05 degrees latitude and 0.05 degrees longitude (which believe me, in Alaska is way too big an area), and if the IDs don’t match, I look within 0.025 degrees longitude and 0.025 degrees longitude. These numbers were chosen extremely arbitrarily, and still causes a bit of a problem with a couple of airports that are near the US/Canada border because when I’m loading the FAA data it changes some Canadian airport to the nearby US airport, and then when I load the Plews data it changes it back.

Testing out my load scripts, I discovered two things:

  1. Sometimes the resurveyed point has moved enough that it’s in a different “area”. And that’s going to confuse the hell out of the algorithm that the app uses for getting updates, because it will ask for updates for the old area, and not get anything for that point. That’s going to require some thought to fix.
  2. In the next FAA data load, they’ve actually moved a couple of airports by 1.0 degrees of latitude or longitude. And judging by what I’m seeing on the Our Airports site maps, it appear the new values are correct, so the old ones must have been a data entry error. In this case, my “match the old” algorithm didn’t find anything to match within its radius of action, so it made a new point and marked the old one as deleted. The app should deal with that nicely.

Hmmm. Need to think how to handle this…

Stackoverflow comes through again

There is a major function in our program called the Migrator. It’s purpose is to “migrate” content from the content storage to the various feature players, either manually under user control or automatically based on what is on the schedule. Unfortunately the original requirements, put in place for a potential customer who ended up going a different way, were that the user had to be able to see and control each individual file in the migration job, and to each destination. This meant there is a tree showing each destination, and all the top level containers (playlists), all the middle level containers below that (CPLs) and then all the individual files (track files, fonts, projector control files, etc) below that, all wrapped up in a nice little collapsable tree. (Thanks to Sun providing an example implementation of JTreeTable on their web site.)
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Is this a first?

I bet there aren’t very many other people out there who have turned in a resignation letter at their job the day they went to pick up a new car. Well, I’ve just done the resignation letter, and I pick up the car in a few hours.

Update I forgot to mention: as well as the offer from Global Crossing, I have another offer from Paychex. The Paychex one surprised me, because I’d only had a phone interview with them and I’m not used to getting a real offer without having a chance to meet people face to face, look around the facilities, etc. Because I was expecting it to lead to a face to face interview instead of an offer, I didn’t ask enough detailed questions about unimportant things like “where are you located?” and “what will I be doing?”

I’ll never understand the thought processes of stupid people

I got an email to the mailman administrator account from somebody claiming that the previous owner of his email address must have been a pilot, and he wants to be unsubscribed from the mailing lists because “they clog up my mailbox”. I run a bunch of lists for pilots, but none of them average more than one message a month, so I wasn’t initially inclined to be kind to him.
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StackOverflow lesson #1

If you care about your “reputation points” (which I keep thinking of as “XP”), don’t go dissing Windows.

A person asked what to do about their parent’s virus infected computers. There were some “real” answers, so I jokingly suggested that they do like I do, and threaten to install Linux on them – that way, they either take you up on the offer and they never have viruses again, or they stop calling you and call somebody else, and it’s a win for you either way.

So far in the last two hours, that question has been voted down 4 times, losing me 8 XP.