xearth and path cross

As a final comment in the geolocation and path cross entry I wrote:

If you think of any good uses for upoints, drop me a mail. Cool new uses with attached patches are even better!

The first chunk of feedback I received was from a co-worker, Kelly Turner, who asked how difficult it would be to use upoints with xearth’s marker files. The answer is not too difficult, not too difficult at all.

As a little background the reason for wanting access to the data in marker files is that our internal contact database allows us to export a file containing a subset of our contact’s known current locations [1]. The original reasoning behind the feature was to allow simple visualisation of a team’s members, for example to quickly locate somebody who is close to a customer’s site.

I’ve reworked the original edist.py script in to something a little more generic, and it also now includes a new module, xearth, that can import locations from an xearth marker file. Unfortunately, I can’t use an example generated from our system because I don’t have permission to publish the data but I’ll give an example of its usage with a public file:

>>> from upoints import xearth
>>> earth_markers = urllib.urlopen("http://xplanet.sourceforge.net/Extras/earth-markers-schaumann")
>>> markers = xearth.Xearths(earth_markers)
>>> print(repr(markers['Cairo']))
Xearth(30.05, 31.25, 'Egypt')
>>> print(markers['Warsaw'])
Poland (N52.250°; E021.000°)

There are plenty of comments in the xearth file, but what you get from the Xearths is a dictionary with the location name as a key, and value consisting of a tuple of a Point object and any associated comments from the source file.

You can use all the methods, such as distance() and bearing(), that are defined in the Point class on Xearth objects.

>>> print("Suva to Tokyo is %i kM" % markers['Suva'].distance(markers['Tokyo']))
Suva to Tokyo is 7253 kM
>>> print("Vienna to Brussels on %i°" % markers['Vienna'].bearing(markers['Brussels']))
Vienna to Brussels on 293°

With the original purpose of the marker file export feature being finding people local to a customer it would be nice to use xearth to do the same in a more programmatic way, and of course that is possible too.

>>> Customer = xearth.point.Point(52.015, -0.221)
>>> for marker in markers:
...      distance = Customer.distance(markers[marker])
...      if distance < 300:
...          print("%i kM - %s, %s" % (distance, marker, markers[marker]))
57 kM - London, United Kingdom (N51.500°; W000.170°)

Imagining for a second the customer lives in my house, the only marker within 300 kilometres of me in the city marker file we’ve imported is London.

I’ll end this entry with similar text to that which created it: If you think of any good uses for upoints, drop me a mail. Cool new uses with attached patches are even better!

[1]	All thanks to Simon Woods according to the source code repository, so a big thanks to him!