[josm-dev] How about virtual layers?

[Frederik Ramm]

Hi,

Tobias Wendorff wrote:
> For example:
> - a highway without layer 0 => virtual layer 0
> - a leisure area with layer +1 => virtual layer 1
> - a building with layer +2 => virtual layer 2
> 
> This would make it possible to edit only the selected layer.
> What do you think?

We need something like that, however it is not easy. I have started 
implementing an extension to the mappaint scheme with two main features:

1. You can have any number of styles and switch between them without 
restarting.

2. Any style can, in addition to saying how a feature should be 
rendered, also say that a feature should be invisible and/or inactive. 
Such an item would then not be editable and not be affected by "select 
all" etc.

This would effectively give you the kind of layers you desire, but even 
more flexible - your style file would determine which objects are 
editable on a certain "layer" (the different styles would be layers), 
and you can create any number of them.

The problem I had when implementing it was that (a) the editability of 
nodes would often depend on whether a way they're part of is editable or 
not. And what if there is a node shared by railway and highway and 
railways are disabled... can you move it then? And (b) the problem of 
tagging something out of your view (you are in a view that hides parking 
lots, now you accidentally tag a node as amenity=parking, and it is 
gone...).

These are not insurmountable but will probably cost some performance of 
which JOSM doesn't have a lot to spare...

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"