[OpenLayers-Users] center crosshairs?

[Mike Quentel]

OpenLayers.Control.Crosshairs = OpenLayers.Class.create();
OpenLayers.Control.Crosshairs.X = 320;
OpenLayers.Control.Crosshairs.Y = 240;
OpenLayers.Control.Crosshairs.prototype = 
  OpenLayers.Class.inherit( OpenLayers.Control, {
    element: null,
    position: null,
    
    initialize: function(element) {
        this.position = new
OpenLayers.Pixel(OpenLayers.Control.Crosshairs.X,
 
OpenLayers.Control.Crosshairs.Y);
        OpenLayers.Control.prototype.initialize.apply(this, arguments);
        this.element = OpenLayers.Util.getElement(element);        
    },
  
    draw: function() {
        OpenLayers.Control.prototype.draw.apply(this, arguments);
        px = this.position.clone();
        var sz = new OpenLayers.Size(21,21);
        var centred = new OpenLayers.Pixel(px.x - (sz.w / 2), px.y);
        this.buttons = new Array();
        var imgLocation = OpenLayers.Util.getImagesLocation() +
"crosshairs.png";
        return
OpenLayers.Util.createAlphaImageDiv("OpenLayers_Control_Crosshairs_" +
"crosshairs", centred, sz, imgLocation, "absolute");
    },
    
    CLASS_NAME: "OpenLayers.Control.Crosshairs"
}); 


Regards,
 
Mike Quentel


-----Original Message-----
From: users-bounces at openlayers.org [mailto:users-bounces at openlayers.org]
On Behalf Of geoman
Sent: Tuesday, 09 September 2008 14:21
To: users at openlayers.org
Subject: [OpenLayers-Users] center crosshairs?


Hello,

I am trying to add a icon that is fixed at the center of a map, to show
where the center is when people are zooming. I didn't see a way to add
an icon to a map directly, and it looks like if I put the icon in a
marker and then add that to a layer on the map then the icon will move
with the map. 

My solution was to add the icon through the DOM (using Prototype:)
				var centerIcon = new Element("img");
				centerIcon.src = "img/center5.gif";
				centerIcon.id = "mapCenter";

				centerImg.setStyle({
					left:
((document.viewport.getWidth() / 2) - (centerImg.getWidth() / 2))
+ 'px',
					top:
((document.viewport.getHeight() / 2) - (centerImg.getHeight() /
2)) + 'px'
				});
	
$('map_OpenLayers_ViewPort').insert(centerIcon);

Here is the styling I used for this element:
  img#mapCenter {
  	position: absolute;
  	z-index: 10000;
  }


Is there a way to do this using the OpenLayers API? If not, can you
offer any solutions with a couple major problems I see with the above
approach:
1. The icon isn't always at the center of the map; it is always close,
but when I zoom in I can tell it is slightly high and to the left. I'm
not sure why it is usually dead-center and sometimes off-center.
2. Markers under the icon no longer receive mouse events. I tried to set
the z-index of the icon so it would be under my marker layer, but my
map_OpenLayers_Container has a z-index of 749 and my marker layer has a
z-index of 350, and I can't set the z-index both above 749 (so the icon
is visible over the map tiles) and below 350 (so the markers will
receive input events). 

Thanks in advance,
Craig


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