Lossy and Lossless Methods Getting OSM Data

This is a question pertaining to osm2pgsql, osm2pgrouting and nominatim.

As I understand it, these are 'lossy' methods for getting data from OSM and into a PostGIS database.

I was wondering:

In which ways are these methods 'lossy' (what data is lost)?

and

are there any known methods that are lossless?

asked 30 May '13, 15:31

FortyLashes
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accept rate: 0%

edited 30 May '13, 19:25

Frederik Ramm ♦
82.5k●92●720●1273

3 Answers:

active answers oldest answers newest answers popular answers

Yes, these are lossy methods. For example, osm2pgsql drops coastlines, and the main outputs manipulate data into OGC simple features, which loses information regarding routing relationships.

You can load osm data into postgres in a lossless fashion using osmosis and the --write-apidb or --write-pgsql outputs, depending on what schema you wish to use.

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answered 30 May '13, 19:12

Andy Allan
12.5k●23●128●153
accept rate: 28%

@Andy Allan Sorry for not getting back sooner! Thank you for that! I have been looking into Osmosis - that is awesome you can do lossless!

(14 Jun '13, 18:06) FortyLashes

The most common lossless DB schemas are apidb, pgsnapshot, pgsimple and OSM3S.

apidb

can store history
is not spatially enabled
uses postgresql
takes weeks to import
takes more than 1TB

pgsnapshot

is current data only
is spatially enabled
uses postgresql + postgis
can have geometries built for ways
takes days to import
takes a couple hundred GB
uses hstore to store tags

pgsimple is pgsnapshot with separate tables for tags instead of hstore

OSM3S

is current data only
is custom database software
is primary used by overpass API

None of them are well-suited for rendering. The main uses for these database types are analysis and when you want to be able to produce a .osm file for an area.

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answered 14 Jun '13, 20:02

pnorman
2.4k●5●21●40
accept rate: 18%

-5

I assume that by "OSM data" you mean the OSM source data and by "lossy method" you mean that the output dataset, after processing it by a "method", contains at least one less (missing) or changed object compared to the input dataset. If these assumptions are correct my answers to your questions are:
-Yes, all "methods" are lossy (regardless of the programing language and source type in apps). Namely, the OSM source data contains many (but really many) errors of formal and logical nature. Some of the erroneous objects must be ignored and many of them are changed by a data-preparation "method". But the data-preparation is done by teams and as a rule teams have different filings for criteria what to ignore, what and how to change and so on. Therefor the "lossy" nature of the "methods" considerably vary. In my opinion/experience about 90% of all errors may be repaired.
-Yes, downloading the latest regular OSM dump will provide you with exactly the same objects as they are in the database of the OSM source data.

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answered 31 May '13, 08:12

sanser
695●38●39●55
accept rate: 5%

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Question tags:

nominatim ×689
osm2pgsql ×263
postgis ×134
database ×118

question asked: 30 May '13, 15:31

question was seen: 5,094 times

last updated: 14 Jun '13, 20:02

Lossy and Lossless Methods Getting OSM Data

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