forceTZ returning unexpected result

[josiekre]

I've been using forceTZ=True to deal with coastal points. Thanks for adding this feature. Seems to be working well except for these rare points in Vancouver.

>>> from tzwhere import tzwhere
>>> tz = tzwhere.tzwhere(shapely=True, forceTZ=True)
2016-06-14 23:34:20,283 tzwhere.py _read_polygons_from_csv 288 INFO  Reading from CSV input file: /home/ec2-user/.local/lib/python2.7/site-packages/tzwhere/tz_world.csv

>>> tz.tzNameAt(49.2698, -123.1302)
>>> tz.tzNameAt(49.2698, -123.1302, forceTZ=True)
'America/Los_Angeles'

It should return 'America/Vancouver' as that's the closest polygon by far. Am I missing something?

[jannikmi]

I really don't want to hijack this post, but since no one answered yet, here is my explanation:

Like in other older issues (e.g. mattbornski/tzwhere#8), probably the timezone data used by this package is slightly off at this exact point (bay areas seem to be prone to errors). The description of this package also describes the forceTZ option as "[...] a somewhat 'hacky' workaround [...]". I actually don't know why the algorithm would return 'America/Los_Angeles' however.

What I think you are actually looking for is a real proximity algorithm. You should consider using my packages option closest_timezone_at(...): https://github.com/MrMinimal64/timezonefinder
See the documentation for more options on this.

Hope I could help. Greetings

[cstich]

I am not completely sure why it doesn't return the correct timezone either. I'll have a look into it.

[josiekre]

@MrMinimal64: Thanks for sharing timezonefinder. What's the difference between tf.timezone_at(*point) and closest_timezone_at()? It's not entirely clear via the description.

@cstich: Happy to help debugging or testing. I haven't had a chance to dig into the algorithm you're using for forceTZ option yet which is why I thought I see if you quickly knew why it was doing this before investing a bunch of time.

[jannikmi]

Hm, that's not good... timezone_at() is the normal function for checking timezones (like tz_NameAt) with just a few optimizations. closest_timezone_at() is a real proximity algorithm (searching for the closest timezone, like the name suggests).

[famanson]

Sorry to barge in after a year, but the reason that forceTz is acting weirdly is because of the distances being sorted using the wrong key

I've submitted a PR here #40, using @josiekre's exact example as test data