[Imports] RFC: LA County building import (Los Angeles, California, USA)

[maning sambale]

Dear Cristoph,

> - Tagging still looks vague.  What you have on
> https://github.com/osmlab/labuildings/blob/master/README.md is just a
> list of OSM keys to use but there is no information on the values -

Right, I updated the wiki to describe the tags.  Still a work in
progress, but see here:
https://wiki.openstreetmap.org/wiki/Los_angeles,_California/Buildings_Import#Data_Preparation

> like what set of values is to be used for building/building:use/amenity
> and what units/reference system are used for numerical values.  This
> will need to be in the wiki and not just somewhere in the code so
> mappers can later look up how certain tags were generated.

We mostly used building and building:use tags. Main concern of not
using the amenity tags is because the building use was based on
parcel/assessor information. For example for amenities like fast_food
there will be several buildings (main resto, parking building, etc)
within the property. If we use amenity, there maybe 3
amenity=fast_food in one parcel.  In addition, we don't want to add
amenities without the names.
For each tag we use, we check taginfo if the tag exist.  If it doesn't
we use buildng=yes.

If you have suggestions on the correct tags please advise.

> - Positional accuracy and actual compliance of the data with OSM mapping
> practice are still unclear.  You observe offsets in
> https://github.com/osmlab/labuildings/issues/43#issuecomment-194957204
> but make the assumption the data to import is accurate.  This is highly
> questionable.  With that volume of data and the connected amount of
> work it would be highly advisable to check it in a few places at
> least - if necessary sending out someone with a high precision GPS.

The initial offset we saw was due to re-projection issues from NAD83
to WGS84 datum.  By using a custom projection parameters the
difference is very minimal difference (10 micrometer precision range).
Reprojection is now step is now added in the wiki.  I admit that there
are still offset in some cases (less than a meter), but they are now
rare compared to when we didn't do custom re-projection.


> Also important to check is for example if overhanging roofs, carports
> etc. are classified as buildings since these are not buildings within
> OSM.

Yes, we checked this as well.  The buildings are actual footprint
based on the documentation and my eyeball for several areas.  Also,
worth to note that we are excluding Pasadena since we observed that
Pasadena data was building parts instead of the whole building.


Thanks!

-- 
cheers,
maning
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