Subject: [Geojson] Concrete example of an antimeridian crossing bbox

From: Sean Gillies <[email-masked]>
Date: Sun, 14 Feb 2016 17:21:54 -0700

In https://github.com/geojson/draft-geojson/issues/133 Martin says that the
draft glosses over details of antimeridian-crossing bounding boxes and I
agree. In https://github.com/geojson/draft-geojson/pull/145 I have a
concrete example of an antimeridian-crossing bbox and its complement:

# Bounding box

...

## The Antimeridian

Consider a set of point features within the Fiji archipelago, straddling
the antimeridian between 16°S and 20°S. The southwest corner of the box
containing these features is at 20°S and 177°E, the northwest corner is
at 16°S and 178°W. The antimeridian-spanning GeoJSON bounding box for
this feature collection is:

    "bbox": [177.0, -20.0, -178.0, -16.0]

The complementary bounding box for the same latitude band, not crossing
the antimeridian is:

    "bbox": [-178.0, -20.0, 177.0, -16.0]

I believe this also addresses the first half of Dirk-Willem's comment at
https://github.com/geojson/draft-geojson/issues/47#issuecomment-175507119.
The bounding box edge interpolation part we should take on in another issue
and PR.

-- 
Sean Gillies

---

From: Martin Thomson <[email-masked]>
Date: Mon, 15 Feb 2016 11:50:39 +1100

That would help lots, thanks Sean, some tweaks and a correction below.

> containing these features is at 20°S and 177°E, the northwest corner is

Important: *northeast*

>     "bbox": [177.0, -20.0, -178.0, -16.0]

I think that it would help immensely if you could note in both the
examples the size of the bounding box.  That is, the above example
covers 5 degrees of longitude and the complementary box covers 355
degrees.

I don't know if this helps, but it might pay to say something like:
"The latitude of the northeast corner is always greater than the
latitude of the southwest corner.  However, boxes that cross the
antimeridian have a longitude for the northeast corner that is less
than the longitude of the southwest."

I know that this is perhaps being overly pedantic, but the obvious
solution here is wrong and I have had too much experience with people
messing this one up.