[OpenLayers-Users] ModifyControl Select/Delete Vertex?

[Robert Smart]

Hi, 

Thanks for a really in depth answer. It really explains it well.

Unfortunately my javascript skills are pretty basic at the moment, so a lot of that went over my head!

I like the sound of the vertexselection event on the vector layer class. Could you give me a few more hints about how this might work?

Or even better give me an example bit of code :)

We would need to be able to access the vertex index of the selected vertex, and i guess there would have to be a method of removing the vertex from the feature, which would trigger a redraw of the feature on the map.

We would have to also be able to define a style for that selected vertex too, and i suppose add some error trap to ensure that we can't select a virtual vertex?

Thanks again,

Rob



On 27 Feb 2013, at 13:51, "Alexandre Dubé" <adube at mapgears.com> wrote:

> Hi Rob,
> 
>   This would indeed be a nice feature to have.  Looking at the ModifyFeature control, I think this could be easily accomplished with minor modifications.
> 
>   If we look at the ModifyFeature control, it creates a DragFeature control to allow dragging the vertices around.  When you "mouse hover" a vertex feature, a callback function is triggered because it was defined here :
>     https://github.com/openlayers/openlayers/blob/master/lib/OpenLayers/Control/ModifyFeature.js#L267
> 
>   That's the callbacks for the OpenLayers.Handler.Feature object the drag control needs to interact with features on the map.  The drag control defines its callbacks method in the featureCallbacks object :
>     https://github.com/openlayers/openlayers/blob/master/lib/OpenLayers/Control/DragFeature.js#L119
> 
>   and here's the list of callbacks you can set to a feature handler: click, clickout, over, out, and dblclick.
>     https://github.com/openlayers/openlayers/blob/master/lib/OpenLayers/Handler/Feature.js#L30
> 
>   So, back in the ModifyFeature control, you could add a 'click' callback function just next to the 'over' one.  Instead of coding what you want it to do directly in the source, just define an abstract function that needs to be overriden OR you could fire an new vector layer event : vertexselected (which would need to be added to OpenLayer.Layer.Vector).
> 
>   Whoa, sorry for the long reply :)   In short, try to create a delegate method or event we could register to to do whatever we wanted on vertex selection.
> 
>   Does that make sense ?
> 
> HTH,
> 
> Alexandre
> 
> 
> On 13-02-26 11:42 AM, Robert Smart wrote:
>> Hi All,
>> 
>> I'm trying to port some existing functionality into open layers and have 
>> managed to get most of it working. I'm just stuck on a seemingly simple 
>> task.
>> 
>> The current code allows a user to highlight a polygon vertex by clicking on 
>> it (which changes its colour), so that the user can then press a delete 
>> button to remove the vertex.
>> 
>> Using the modify control I'm able to display the vertices, and even delete 
>> them if I click on it and then press 'del' on my keyboard, but this is not a 
>> great solution as there is no visual clue as to what vertex has been 
>> selected.
>> 
>> So is there a way to highlight or change the colour of a single vertex the 
>> user has clicked on? is there then a way to remove that vertex via code and 
>> have the polygon redraw on the screen to suit?
>> 
>> I think this would actually be quite useful as a standard feature as there 
>> are many cases where one might want to select an individual vertex.
>> 
>> Thanks,
>> 
>> Rob
>> 
>> 
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> 
> 
> -- 
> Alexandre Dubé
> Mapgears
> www.mapgears.com
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