I’m thinking about a design for an efficient storage container for OSM PBF
(planet size data, minutely updates), for the purpose of TileMaker as well as
for an internal application.
One thing I stumbled on is the usage of the bounding boxes within OSM PBF. The
documentation [1] does not clarify on the spatial characteristics of the
individual FileBlocks. Some questions:
1. Is it correct that there is exactly one HeaderBlock in a .pbf file? If
so, the BBOX defined within the HeaderBlock defines the whole region of the
.pbf export?
2. What are the spatial characteristics of an individual FileBlock within
the FileBlocks sequence? Is a FileBlock generated by any kind of spatial
ordering? For example, is it save to assume that all content is very dense /
close to a region of the world? Or can this be controlled when creating a .pbf?
If there was a spatial loose relationship, it would allow to relate FileBlocks
to map „tile“ regions (a FileBlock may obviously relate to several „tiles“, but
would be fine as long as the blocks relate to a certain region for most of it’s
content)
3. There is a commented BBOX definition within the PrimitiveBlock. What
remains to be done to to enable this proposed BBOX extension? I’d have the same
question about this BBOX as with my second question.
message PrimitiveBlock {
….
// Proposed extension:
//optional BBox bbox = 19;
}
I’d add an additional parse step to create this spatial relationship, if there
is no spatial relationship yet or the spatial characteristics are not „good
enough“.
~Ben
[1] http://wiki.openstreetmap.org/wiki/PBF_Format
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