[talk-au] JOSM Scanaerial plugin on NSW LPI layers

Andrew Davidson u887 at internode.on.net
Fri Jan 22 13:36:21 UTC 2016

You can extract the geometries from the database directly, you don't have to scan them. I tried this on three park areas to see how much work was involved. The recipe I followed was:

1. Use the query tool to find out how many objects have the name that you are looking for. You do this with:


with the return format set to html. Names must be in upper case and you need to see what object ids are returned. For example if you search for Yanununbeyan with:


You get three different ids (198,208,1131) because there is a Yanununbeyan State Conservation Area, Yanununbeyan Nature Reserve, and Yanununbeyan National Park. All of which need to be tagged differently. Follow the object links to find out what type of area they are.

2. Having found the object id you need you get the geometry by using the query tool and setting the object id, setting the output spatial reference to 4326 (WGS84), and changing the output format to JSON.

3. Save the resulting page, say output.json

4. Use ogr2ogr from GDAL to convert the output into something JOSM can read:

ogr2ogr -f "KML" output.json output.kml

5. If you have the opendata plugin installed you can open output.kml in JOSM.

6. Use the simplify way option in JOSM as there are far too many points in the resulting kml. I personally thought that the default 3m looks OK.

7. Tag the ways with an appropriate source:geometry and add a note to the effect that the way has been simplified using a max error criterion set to whatever you used.

8. Now comes the difficult and time consuming bit. You have to cut up and conflate the new boundaries with the existing data as you merge each new way from the layer you opened the kml in to the layer the osm data is in. This is the step where you could really make a mess. 

I found while doing the few test cases that I had to:

- Make sure that common boundaries use only one way (which means that the more parks, state forests, admin areas, etc that share ways the more time consuming it gets)

- Make judgement calls about if you should use the new boundary or keep the existing way where the boundary is something physical on the ground like a river bank or coastline. This is why I tagged the new ways with source:geometry so other mappers can see where they came from.

- If there are already ways in place, using the replace geometry function of the utils2 plugin to try and preserve history.

The cases I tried as a test were:

South East Forest National Park:

Murramarang National Park:

Clyde River National Park:

The South East Forest case was a multi-hour mapping marathon as the park has a lot of separate sections and shares many boundaries with neighbouring state forests and parks. The other two were much simpler but Murramarang need more time than Clyde River as it has more sections and shares a lot of common ways with the coast and various rivers.

As to the import question it seems to me that there is a tacit agreement that tracing the boundaries one at a time is acceptable (not sure what the rest of OSM would think about this). Given that the biggest problem with an import would be conflating the data with the existing, provided that we're carefully hand-crafting each park I think we're OK. Does anyone have a differing opinion?

On Tue, 19 Jan 2016 13:44:12 +1000
Nev Wedding <nwastra at gmail.com> wrote:

> Should the JOSM Scanaerial plugin be able to scan the LPI NSW
> Administrative Boundaries NPWS Reserve WMS layer and others. I would
> like to zoom in to a section and use the plugin as an initial pass
> instead of manually mouse clicking around the long and winding
> boundary and then refine the result before tagging and uploading.
> https://wiki.openstreetmap.org/wiki/JOSM/Plugins/Scanaerial	
> I am using a mac OS X and there are no instructions for that install
> so I may not have it set up correctly yet, so first up before
> proceeding further, I would like to know if it will help anyway. 
> I am unfamiliar with tracing shapes other than tediously wandering
> around the boundaries one click at a time.
> I played around with Gimp and Inkscape but found that to be quite a
> task too and wasn’t sure if I could use the output in Josm in anyway.
> How do you manage such tasks? Are their special mouse tools available?
> Is what I am trying to do essentially considered to be part of an
> import and/or the current LPI layers unsuitable for the tracing
> process.
> Some links to where to find more info on this topic would be
> appreciated. _______________________________________________
> Talk-au mailing list
> Talk-au at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/talk-au

Andrew Davidson <u887 at internode.on.net>

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