[osmosis-dev] Maven artifacts, using Osmosis as a library, OSMembrane

[Igor Podolskiy]

Hi Andrew, hi everybody,

> I see that there has also been some discussion on the list about using
> Osmosis as a library (quoted message below). Igor, based on a quick look
> at PipelineExecutor in the head revision of OSMembrane, it looks like
> you are calling Osmosis as an external program.
yes, OSMembrane spawns off an external process. This is partly the 
heritage of OSMembrane being a student project, partly it's a deliberate 
decision. For example, Osmosis can potentially consume lots of memory, 
and you don't want your pipeline chewing off large chunks of the 
pipeline designer process' memory. You might want to control how much 
memory Osmosis gets (-Xmx...), which is not necessarily the same amount 
you want OSMembrane to have. So while the whole roundtrip of generating 
a command line just to feed it back to the Osmosis command line parser 
can (and probably should) be avoided, OSMembrane will always spawn a new 
Java VM with an Osmosis pipeline, independent of the degree of 
integration. That being said, it's no requirement imposed by Osmosis, 
it's an OSMembrane thing - so if you want an Osmosis pipeline in your 
OTP process, just do it :)

> Are you still planning
> to tighten the integration with Osmosis? What has been your experience
> using Osmosis in this way?
Yes, planning... unfortunately, I have not nearly as much time for it as 
I would like to :(

In any case, using Osmosis as a library is fairly easy - although 
there's no complete tutorial for that, the Osmosis' very own unit tests 
are basically a blueprint of what you should be doing. For example, look 
at [1].

At the very basic level, you instantiate the entity processors you need 
(objects implementing Sink, Source and SinkSource interfaces) and feed 
them the EntityContainers somehow. If you read from an XML/PBF/etc. data 
source already supported by Osmosis, you can use the reader Sources 
shipped with Osmosis; if you want to feed it data directly from your 
code, you'll have to write your own Source or RunnableSource. Similarly, 
at the other end of the pipeline, you'll need to install a Sink of some 
kind. For an example of this, take a look at the SinkEntityInspector 
which simply buffers up every EntityContainer it gets in a 
List<EntityContainer> [2].

I hope I could tip you off in the right direction - if you have 
questions about Osmosis integration or OSMembrane, just ask them here, 
I'll try to help.

Greetings from Stuttgart,
Igor

[1] 
https://github.com/openstreetmap/osmosis/blob/master/set/src/test/java/org/openstreetmap/osmosis/set/v0_6/MergeBoundTest.java

[2] 
https://github.com/openstreetmap/osmosis/blob/master/set/src/test/java/org/openstreetmap/osmosis/test/task/v0_6/SinkEntityInspector.java