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

[Ross]

On 25/01/16 11:58, Ian Sergeant wrote:
> Hi,
>
> The road is a vector, representing the road.  It does not represent 
> the road centreline. It has properties, such as width and lanes, and 
> sidewalks.
>
> If the boundary *is* the physical feature, then it is not corrupting 
> the data by making it align with the physical feature. If the boundary 
> is not the physical feature, then don't align it.

How do you know it is the physical feature?

Just because it follows approximately the feature does not mean it is.  
When originally gazetted the physical feature may have been located 
differently (roads, railways realigned, rivers making new paths)  Don't 
automatically assume that the feature is still in the same place without 
looking at the imagery or physical survey.  Don't assume that the 
boundary changes to the new position of the road, etc.


>
> The NSW/Victorian border has been done entirely along the riverbank.  
> Much of it by me and a few others after you guys decided to take your 
> bat & ball.  So, I don't believe this is actually an issue.  Do you 
> have any examples of where this is a concern?
>
No.  It was just an example of were an incorrect assumption had been made.

> Tracing the actual border between NSW/Victorian border was actually 
> quite interesting.  You have the gradual accretion or divulsion to 
> consider, and it is clear the LPI data is not necessarily aligned with 
> what is current.  Most of the border that I've traced I'd consider to 
> be more current than the LPI data, and I'd certainly want to thrash it 
> out before someone started replacing it with yet another import. We've 
> had so much ugliness in the past with these imported data sets with no 
> follow up.
>
But the border has not changed the river might have but there is no 
change to the border from when it was first surveyed/gazetted.  The 
border is the line as when gazetted, not as where the riverbank is now.

An example of this is here:

https://www.openstreetmap.org/#map=17/-36.19879/148.03658

Open it in josm then open the nsw imagery, and the nsw basemap and you 
can see where the river was originally and where the border runs.


Cheers
Ross

> This issue doesn't come up too much with property boundaries - that 
> are defined independent of the roads.  It does come up with rivers and 
> coastline, and other areas where the physical feature is what is the 
> boundary.
>
Ian.
>
>
> On 25 January 2016 at 11:09, Ross <info at 4x4falcon.com 
> <mailto:info at 4x4falcon.com>> wrote:
>
>     In Australia all property boundaries are not the centreline of the
>     road there is always a road reserve as Andrew pointed out.  So
>     simple do not make boundaries the road.
>
>     Likewise be very careful assuming the boundary is the centreline
>     of a river.  eg the NSW Victoria border along the Murray River. 
>     If you don't know it's actually the southern river bank.
>
>     Realistically with these boundaries if you move them to align with
>     any physical  feature then you are corrupting the data.  Also  if
>     you make the boundary part of a physical feature without checking
>     the full length of the boundary then you are corrupting the data
>     again.
>
>     It's really much cleaner and easier to just import/trace the
>     boundary.  If this shows up where a road/railway/whatever should
>     be then trace it from the imagery as a separate way and tag it
>     appropriately.
>
>     Cheers
>     Ross
>
>
>
>     On 25/01/16 08:53, Ian Sergeant wrote:
>>     On 25 January 2016 at 09:29, Andrew Davidson
>>     <u887 at internode.on.net <mailto:u887 at internode.on.net>> wrote:
>>
>>          The boundaries of the parks and forests are not going to be
>>         roads as they consist of a number of property lots that get
>>         declared for that purpose. Property boundaries don't run down
>>         the middle of the road, they'll be offset (at times the
>>         existing road isn't within the road reserve anymore). 
>>         Property boundaries can be rivers (bank or thalweg depending)
>>         or the MHWM (also known as the "coast" in OSM).
>>
>>
>>     If OSM was only a colouring-in exercise, then this would be
>>     straightforward.
>>
>>     However, roads in OSM are a vector representation of the road. 
>>     And is is very common for the boundary of an area to be the road
>>     itself, that is there is no small gap between the area and the road.
>>
>>     When the boundary of an area *is* the road, then I think it's
>>     entirely correct to include the ways that make up the road in the
>>     multi-poly that defines the area. Even though the vector nature
>>     of OSM slightly expands features that are 2 dimensional when they
>>     are adjacent to features that are 1 dimensional. The data is correct.
>>
>>     Of course, if the boundary isn't defined by the road, but just
>>     happens to be close to it, then that's different.
>>
>>     Ian.
>>
>>
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