• Voids – SRTM has “no data” gaps in certain places of the world, where the radar reflections went haywire. These happen in marshes (not of interest) and mountains (of great interest!), especially over the Alps. ASTER is void-filled already, so the clever-but-inaccurate void-filling I use wouldn’t be necessary
• Resolution – It’s great that SRTM covers the whole world, but I’d love to see it at a higher resolution. ASTER’s nominal resolution is three times greater than SRTM, so it’s very attractive.
• Arctic coverage – SRTM only goes as far north as 60°N, which is a bit of a problem in Scandanavia. Although there’s GTOPO30 data for these areas, that’s got a horizontal resolution measured in kilometres, so not exactly great for me. ASTER covers those areas too, up to 83°N.

So far so good. But when I started work with ASTER in December, things spiralled rapidly downhill. First is the pointlessly irritating “order a dataset” website, that sucked up hours of going round in circles. It’s like a shopping website from 1999. You need to use a stupid interface to order which 1°x1° tiles you want, and “All” isn’t an option, despite there being 22,600 of them. It seems geared up for people who want a couple of dozen at a time, and the whole thing has a feel of being run by men with beards and sandals who’d rather you didn’t use their website in anything newer than Netscape 4 on HP-UX.

When I read the README alarm bells started ringing. There’s a section on “mole runs” and “pit artefacts” that sounded a bit worrying, but I wasn’t sure how much of an issue they’d be – if they were small and few and far between then that’s not much of a problem. But the biggest thing that caught my eye, buried on page six after pages of confirmation of how good the accuracy was, right at the end of a section as a throwaway comment, was the following statement:

Also, while the elevation postings in the ASTER GDEM are at 1 arc-second, or approximately 30 m, the detail of topographic expression resolvable in the ASTER GDEM appears to be between 100 m and 120 m.

That’s a bit of a bomb-shell – it’s saying that although it’s got a much higher nominal resolution than SRTM, it’s effective resolution is about the same – there’s not any more actual detail, just more pixels. That was almost enough to make me give up there and then, but it’s still void filled and covering more area of the planet, which would be good improvements. So I grabbed the DEM (thankfully, they’re straightforward GeoTIFFs) and got to work over Snowdon. I did some colouring and contours, and they both looked excellent and much better than what I made from SRTM. But then I tried hill-shading, and disaster!

Here’s the area around Snowdon (click through for original size):

and a detail of Snowdon itself:

The mole runs are everywhere – all across that image, even on the flat bits. And the pit artefacts are huge – the size of quarries, and really, really obvious. I honestly can’t use that – maybe for a “what the world would look like if it looked like the moon” project, but nothing more serious than that. And considering that SRTM has only a handful of single-pixel voids in that area, the guys making ASTER have made something that’s substantially worse than an oversampled SRTM. And considering they were even using SRTM to fill the gaps in the ASTER data, that’s a pretty poor show. I started reading around and found a few people saying similar things. And when I though about it, the “improvements” to the contours I saw could be recreated with SRTM by using gdalwarp to artificially increase the resolution (with some nice smoothing) before generating the contour lines. So I gain nothing from ASTER in the 95% of the planet that doesn’t have significant voids, and in that same 95% it’s not really usuable.

So for now, I’ve given up with ASTER. I might revisit it for the band between 60°N and 83°N, but it also says in the readme they have voids over eurasia for that area (so much for void-filled, eh?). And it would be interesting to see if someone can fill the large SRTM voids with ASTER (which sounds back to front, hey-ho), but I don’t have time for that. However, as they say in the docs, all these artefacts are happening in the boundaries where they have different numbers of original samples, so maybe a future version will have these automatically smoothed out, and it they can figure out how to stop their 15m sampling getting turned into 120m effective resolution, that would be awesome. But for now I would say it’s not worth using it.

So the moderation is back on again, but only for first time posters (first time since I upgraded a few weeks ago, I think that is). I’m especially disappointed that Askimet didn’t pick up on comments which were exactly the same format as the previous 200 that I had got.

Still, it’s not really the plugin’s fault – one day, there will be much vengenance wreaked by everyone who has ever run their own blog…

Now if only I knew of an organisation that had both ladders and pots of black + white paint to hand. Hmmmm….

(For those of you trying to avoid being roped into caring about the election, feel free to ponder the joys of being able to link directly to a blog category instead of a collection of individual posts. Nice.)

(And for those of you who are really into the whole election thing: “Compulsory voting : bringing an end to low turnout caused by intimidatio and negative campaigning. Discuss.”.)

And I feel ill, which isn’t helping.

By default, Thunderbird only checks your Inbox for new messages (which stems from a POP3 legacy). If you have server-side rules (or use a web interface to do your rules), then you’ll want Thunderbird to check subfolders as well. This can be done by right-clicking the folder in question, selecting properties, and ticking the appropriate box. There’s no(t yet an) option to do this globally.

Applies to Thunderbird 0.9.

Update: April 2008

Years later, even with Thunderbird 2.0, this is still a problem. But there’s now a global option, thankfully. Although it’s completely hidden, it saves a lot of time if you’ve got lots of subfolders.

Open up the preferences dialog (either Tools -> Preferences or Edit -> Preferences), and click Advanced -> General -> Config Editor. In the filter box start typing ‘mail.check’ and then double click on mail.check_all_imap_folders_for_new. It should then change the value to true (and it’ll appear in bold since you’ve changed it) and all should hopefully be hunky-dory.

I’m not going to turn on comments for them though, and I’m not going to go through them all and try classifying them, since that would be a bit boring.

Today’s exercise in coding reminded me again why I’ve made the switch from a home-grown weblog to using a properly developed one (not quite off-the-shelf or shrink-wrapped, but you know what I mean). Next time I want to change backend, I know that someone else will have written an import script, and I won’t have to bodge one together myself. And now that I’ve spent about two working-days on the switch, I’ve gone from entering data into the database by hand, to having a proper admin interface, categories, sub-categories, comments, pingback and trackback, drafting, private entries, searching, linkrolls, plugin interfaces… which would have taken quite some time if I’d done it myself. And every time I’m in the pub, or sleeping, or whatever else, I know someone else is improving the software that runs my weblog. Which is nice. And I was getting fed up of the whole wheel-reimplementation thing anyway.

After climbing, we went to the annual Ball Games in the Park, where we all had fun making up new rules in order to get people ‘out’, since our collective rule-making-ability was far superior to our actually-playing-softball skills. Although Ed was pretty impressive with his one-man-team effort. And the rain didn’t stop play, it just happened to coincide with afternoon tea.

The BBQ at the Putney flat was as good as ever, but I’m slightly concerned as to just how many of the word to South Park the movie I know. Especially considering I haven’t watched it for quite a long time.

As an experiment, I’m going to leave the comments activated. I don’t know what will happen with spam and stuff, but we’ll see.

Secondly, I’m making a bit of a break from the past. Amongst other things, I’m trying out WordPress, which even in typing this post has spelled the death-knell for my old home-grown weblog software. Never did get round to replacing phpMyAdmin as the backend. And since I can’t be arsed (yet) importing all my old entries, I’m running this as a separate weblog for now.

I’ve got some heavy-duty faffing to do to make it fit into the rest of the site, so it could be a few days before everything works properly. So keep your hands inside the vehicle, and hold on tight.

Wave goodbye to ‘Chasing Rainbows’, and bid hello to ‘Shine’.

In the meantime, have fun, and look after each other.