Snapping while digitizing vectors

[jachym]

Add a configurable snapping agent. The agent can be configured to listen for edits on a source layer and will look for eligible features on any number of target layers. Separate node, edge, and vertex tolerances can be configured. Snapping precedence is configurable (default is node, vertex, edge).

[jachym]

Snapping while digitization

[euzuro]

from a cursory reading, this seems like kind of a cool patch. does this maybe already work in vectors in trunk? why hasn't this ticket gotten any traction?

I'm putting it into 2.7 now just to force someone to comment on it, move it, or close it.

[pgiraud]

I would like to inform you that there is also some work done by Frederic Junod on snapping too. It's available in a sandbox.  http://dev.openlayers.org/sandbox/camptocamp/feature/examples/modify-feature.html

The approach is different but this already works. I remember that Fred wanted to separate this into several tickets. The first one is at  http://trac.openlayers.org/ticket/1192

[fredj]

The up to date version is now: browser:/sandbox/camptocamp/snapping

[tschaub]

(In [8605]) Add a snapping agent for snapping vertices to nodes, vertices, or edges while editing vector features (creating new sketches or modifying existing features). Provides configuration options for multiple target layers with (optional) specific tolerance values for each target and each snap type. Implemented as an independent control. (see #954)

[tschaub]

See the snapping proposal page? for a bit of detail on a proposal for an alternate implementation (and the draft control).

[openlayers]

This looks awesome.

One thing to add might be the ability to snap in freehand mode as well (as it seems this is not supported in the sandbox example). This would allow for easier 'tracing' of existing adjacent geometries.

-dane

[tschaub]

(In [8631]) Call the modify callback when adding new points. For the snapping control, this allows snapping while in freehand mode (see #954).

[tschaub]

add a snapping agent

[tschaub]

Depends on #1966.

[tschaub]

Tests pass and example works in FF 3, IE 6, IE 7, Safari 3, Opera 9.6. Thanks for any review.

[ahocevar]

Tim, this is great work. The only thing I'd like to add is that in the example, you don't add the control to the map. I see that addToMap is not required for the snapping control, so it may be ok. On the other hand, users may wonder why this control works without adding it to the map.

Anyway, that's minor. Feel free to decide whether or not to change the example in that way. This is good to commit.

[fredj]

Thanks for all your work Tim !

[tschaub]

Replying to ahocevar:

Tim, this is great work. The only thing I'd like to add is that in the example, you don't add the control to the map. I see that addToMap is not required for the snapping control, so it may be ok. On the other hand, users may wonder why this control works without adding it to the map. Anyway, that's minor. Feel free to decide whether or not to change the example in that way. This is good to commit.

Thanks for the review. I'll happily commit.

Adding a control to the map calls control.draw. This creates an element node (control.div) and sets a "selectstart" listener on that element. When the map is destroyed, the controls are destroyed, but the listener on the control.div is never cleaned up. This leaked on unpatched IE6 (at least). I know the right thing to do is patch this - but I also don't really see the point in having the extra element node created.

When this control is activated, a number of listeners are registered on a number of layers. These are only application events (not browser events). When the map is destroyed, the layers are destroyed and their events instances are destroyed (this essentially just removes some arrays of functions - again, this control is not dealing specifically with browser events on element nodes).

Anyway, I'm happy to change the example if people want consistency. I'd also like to come up with an alternative to controls that create needless element nodes.

[tschaub]

(In [8951]) Adding a snapping agent for snapping geometry components to existing components while editing. r=ahocevar (closes #954)