Plugin Request

[Bernhard Hiller <bhil@…>]

Hi there,
I’d like to suggest the development of a new plugin.

Purpose:
Easy tracing of areas from aerial images.

Simplified use case:
In JOSM, the user has selected some aerial images as background, that layer is visible. The user sees an area which he wants to trace. He clicks somewhere in it, the active plugin automatically draws the boundary of that area. It adds the last user defined tag(s) to the way, and also automatically the appropriate source tag. Then the user clicks into another area to be traced. The node originally generated by JOSM is removed.

Examples of areas to be traced in such manner:
Lakes, fish ponds, buildings.

Further points to consider:
Installation and configuration:
For a wide-spread use of the plugin, its installation must be simple, and its configuration must be typically automatic.

Interaction with the WMS plugin:
It must be able to automatically detect the type of aerial images. With the WMS plugin being used for showing the images, some communication with the WMS plugin is required.
It is appropriate for the plugin NOT to get the images directly from their original location, but to use the cached data of the WMS plugin. Do not forget users with low internet bandwidth.

Activation/Deactivation:
Since the left mouse click is normally used for adding a node in JOSM, an easy switch between the "normal" mode and this plugin mode is required. This could be achieved with an icon in the toolbar of JOSM, showing the present state of the plugin, and changing it when clicking on it.
A short cut key combination may be additionally provided, but when tracing the mouse is the appropriate tool in the user’s hand.

Tags for the automatically traced way:
The user can configure one (optionally: several) tags to be automatically added to the way which has been traced automatically. Examples: "building=yes", "natural=water". A menu or toolbar icon must be provided to reach this configuration.
The configured tag is used upto the next configuration change.
A source tag is always provided, e.g. "source=Bing"

No fully automatic tracing:
This plugin expects a semi-automated way of work. A human user is a master of seeing objects from images, far better than any present software. And he is capable of seeing that two fish ponds next to each other are both fish ponds even when one of them is bluish while the other grew green with algae. Red or blue roofs of houses can be distinguished from the area around, and the human user recognizes both of them as the roofs of buildings.

Some hints to the programmers:
We should expect the user to click somewhere into the object he wants get traced, a few pixels away from its boundary. The object has a color different from its surroundings, and though the color is not exactly the same for each pixel of the object, it is quite similar. It should be a good guess to assume that the object can be traced with the color shades identified within those few pixels around the point of the mouse click.
In case the object to be traced extends beyond the visible area of the screen (e.g. estuary mouth of a river), the object is assumed to end where the visible area ends.
Rather than extending an object into infiniteness, return early a failure message.
Expect the zoom level of the image to be adequate, it is not necessary (or even not adequate) to load images at a higher zoom level. If for some reason the plugin thinks that a different zoom would be better, it should show such a message to the user.