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on December 22, 2018

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Using OpenStreetMap osm2pgsql data in Grass GIS

These are my notes on using the OSM data as imported by osm2pgsql in a PostgreSQL database with Grass GIS. While Grass is a very powerful tool, it's Unixy feel is a little disconcerting. If you're a programmer like me, it helps to realize the Grass command line shell is in fact a preconfigured bash session: GRASS 6.4.1 (OSM_900913):~ > ps ax | grep "$$" | grep -v grep 98804 s000 S 0:00.06 /bin/bash The things you get from Grass are a set of binaries that interact with the data you have (organized in locations that are part of a mapset stored inside your filesystem). The other thing that is somewhat unexpected for a PostGIS user is that, within a Grass location , all the data has to share a single projection. Creating a location for your OSM data The first step required when using OSM data is to create a Grass location for the OSM data. I've used the same projection osm2pgsql uses when importing, the "fake" projection with SRID 900...

Using divert sockets on Mac OS X

A note of caution: using the ip firewall, especially at the programming level makes it very easy for you to lock yourself out from the box. I cannot guarantee that you won't loose any data because you've had to reset your computer to regain access so please be careful. About divert sockets One of Tiger's heritages from the BSD world is the ip firewall extensions and APIs. ipfw allows you to use divert sockets. A divert socket is a network socket, that once bound to a specified port will receive all packets diverted to that port. This means you can let the kernel know that you want it to divert all incoming HTTP TCP traffic to port 8787: 00001 divert 8787 tcp from any 80 to 193.231.199.23 in once ipfw has loaded this rule, a divert socket bound on port 8787 will be able to read all incoming TCP packets. The beauty of it is that you can re-inject the packet on the network, even after you've altered it. Our sample program Our demonstration program will look for the string...

A failing disk and the first time I see S.M.A.R.T. actually working

One of the disks that are part of the software RAID powering loudhush.ro has developed a bad sector. The bad news arrived via email, thanks to smartmontools: The following warning/error was logged by the smartd daemon: Device: /dev/hdc, 1 Currently unreadable (pending) sectors For details see host's SYSLOG (default: /var/log/messages). The good news is you can tell the disk to re-allocate the bad sector somewhere else. I've followed the instructions here: BadBlockHowTo.txt , almost to the letter (I did some additional work removing the disk from RAID), and now the disk looks better. I still have to replace it, since a bad block is likely to be followed by others but it's somewhat reassuring to know that smartmontools is smart enough to help.

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