If a polygon is smaller than the largest polygon in our dataset of
simplified polygons then we’re only throwing away useful detail by
simplifying it.
We should still simplify larger polygons as a fallback, to avoid sending
anything to the CBC that we’re not sure it will like.
The thresholds here are low: we can raise them as we test and experiment
more.
Here’s some data about the Flood Warning Service polygons
Percentile | 80% | 90% | 95% | 98% | 99% | 99.9%
-----------|-----|-------|--------|---------|---------|---------
Point count| 226 | 401.9 | 640.45 | 1015.38 | 1389.07 | 3008.609
Percentile | 80% | 90% | 95% | 98% | 99% | 99.9%
--------------|-----|-------|--------|---------|---------|---------
Polygon count |2----|3------|5-------|8--------|10-------|40.469
We don’t store everything that comes in the CAP XML when someone creates
a broadcast via the API.
One thing we do store is `<identifier>` (in a column called `reference`)
which is a unique (to the external system) identifier for the broadcast.
We show this in the front end instead of the template name, because
broadcasts created from the API don’t use templates.
However this ID isn’t very friendly – the Environment Agency just supply
a UUID.
The Environment Agency also populate the `<event>` field with some human
readable text, for example:
> 013 Issue Severe Flood Warning EA
(013 is an area code which will be meaningful to the Flood Warning
Service team)
We should show this in the UI instead of the reference. The first step
towards this is storing it in the database and returning it in the REST
endpoints.
Later we can have the admin app prefer `cap_event` over `reference`,
where `cap_event` is present.
We can’t backfill this data because we don’t keep a copy of the original
XML.
Seems like `<event>` is a mandatory property of `<info>`, so we don’t
need to worry about the field being missing (`<info>` is optional in
CAP but we require it because it contains stuff like the areas which
we need in order to send out the broadcast`).
***
https://www.pivotaltracker.com/story/show/176927060
If a polygon is smaller than the largest polygon in our dataset of
simplified polygons then we’re only throwing away useful detail by
simplifying it.
We should still simplify larger polygons as a fallback, to avoid sending
anything to the CBC that we’re not sure it will like.
The thresholds here are low: we can raise them as we test and experiment
more.
Here’s some data about the Flood Warning Service polygons
Percentile | 80% | 90% | 95% | 98% | 99% | 99.9%
-----------|-----|-------|--------|---------|---------|---------
Point count| 226 | 401.9 | 640.45 | 1015.38 | 1389.07 | 3008.609
Percentile | 80% | 90% | 95% | 98% | 99% | 99.9%
--------------|-----|-------|--------|---------|---------|---------
Polygon count |2----|3------|5-------|8--------|10-------|40.469
We don’t support these methods at the moment. Instead we were just
ignoring the `msgType` field, so issuing one of these commands would
cause a new alert to be broadcast 🙃
We might want to support `Cancel` in the future, but for now let’s
reject anything that isn’t `Alert` (CAP terminology for the initial
broadcast).
Other systems we’re working with won’t easily be adapted to emit JSON
instead of CAP, so it’s less work for us to do that conversion.
This commit adds to code to parse the XML and turn it into a dict that
we can work with, including converting the polygon string into native
Python lists.
