Comments on: Olson code timezones geekery

By: anselm

anselm — Wed, 20 May 2009 23:53:50 +0000

Didn’t benchmark. I guess it would be something on the order of 50 instructions in assembler? There might be a page fault or two if the entire thing was memory mapped… It operates in linear time… It won’t be as accurate as a vector test unless the resolution of the raster exceeds that of the vectors… I’d benchmark it if there was any conceivable contender for a faster solution :-). Note I should credit Theo Deraadt for suggesting the approach.

By: Ralf

Ralf — Wed, 20 May 2009 23:25:22 +0000

yeah, me too. did you benchmark a little? Your solution sounds so interesting. That’s why i am interested in the average speed of your look up. I am on a 2.8 GHz Intel and once the tree is build up, a look up takes appr. 0.102279 milliseconds.

And, do you get the same error for some locations around coastlines? The above given location is not in any time zone from the shapefile!???

Thanks! Ralf

By: anselm

anselm — Wed, 20 May 2009 22:20:01 +0000

Thanks! I have a hard time imagining how to make it faster – it is just a bitmap peek….

By: Ralf

Ralf — Wed, 20 May 2009 22:09:09 +0000

wow. i like your solution with the colorpleth. did you run any benchmarks on this? how long does a lookup take? i was struggling exactly the same problem a few days ago. i am using a prtree and feed it with the timezones polygons.

i am using the same shapefile, which is sometimes kinda inaccurate (check this lat/lon: 28.4051872, -80.6058589). do you get the same error? for this, i use a function that calculates the standard time zone (not political, no DST!):

http://home.tiscali.nl/~t876506/Multizones.html#iw

nice work! ralf