Posts Tagged ‘dted’

Ocean distance from station

Saturday, December 5th, 2009

Only needs a small change to the map-drawing Java to take the NOAA list of stations and calculate their distances to the nearest ocean. There are 30800 of those so it’ll take a while, but I should then have a map of station ID to distance-to-ocean. Yay!

Distance to ocean map

Saturday, December 5th, 2009

Well, the DTED collection took rather longer than it should have – having to dig around for all the flyspeck islands in the pacific. I’m still not sure I’ve got them all, but it’ll do for now.

I’ve updated the map-drawing code to calculate Great Circle distances between points, and therefore calculate the nearest ocean to each point of land:

(The image contains the actual values obtained, (red*16) + (green & 15) = distance in km. The red channel alone is probably sufficient given the accuracies.)

This is only rough, as it is working at the level of 1-degree x 1-degree cells, so distances are only accurate to around +/-50km. This can be improved by using the data in the DTED cells, rather than just their existence, and should get to well under 1km errors in the temperate latitudes, but for a quick test it’ll suffice.

Data collection

Saturday, December 5th, 2009

Yesterday and this morning I’ve collected a huge number of DTED files from here.

The terrain information is made available for free from the USGS, but is generally provided on physical media as it’s so large – multiple DVDs for level 1 DTED. Of course, there’s no such thing as a free lunch, so the files are grouped into 10-degree blocks and then arranged by country, so somewhat awkward to find – or a fun geography quiz, if you prefer!

I’ve also cobbled together a bit of Java to produce a map showing which terrain cells I’ve got. Sadly, this shows I’ve got some more work to do: