[GIS] Clear markers from OSM map with openlayers

openlayers-2openstreetmap

I have a bunch of Point data that refreshes every few minutes. To render these points, I have created the markers as OpenLayers.Feature.Vector Objects and added them to my Vector layer. The layer gets added to the map object, and I can see the markers when the page loads.

When the data refreshes on my local server, some points from the previous dataset may have disappeared and some new points may have been added. I am just given a large list of points to render every refresh.

Because of this, I need to clear the vector layer of all current markers and then re-render the map with the new dataset.

Also, is there a way to delete specific markers given just a lat,lng? Or is there some way to reference them and delete it from the vectory layer?

How do I clear the vector layer of all markers and how do I delete specific points?

Best Answer

Clearing is done with removeAllFeatures:

pointLayer.removeAllFeatures();

You can remove any that you've stored with removeFeatures:

var aFeature;
//set aFeature somehow 
pointLayer.removeFeature([aFeature]);

If you need to find them by location (lat long) I'd look into selecting the features with a spatial filter then removing them with removeFeatures.

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I would personally go with features over markers. Point features (and all features) allow for labeling and can be represented in different shapes and colors like circles, x, square and so forth. Not to mention all the additional intrinsic functionality and flexibility features have over markers such as geographical calculations, transformations, click/highlight/select handlers and on and on.

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I hate to be pushy, but it would be beneficial if you used something like GeoServer or MapServer on the back end. You could set a WFS strategy that works on your 5-30 second (or whatever) interval timer and allow it to fetch and render the features automatically. In case you're wondering, it already does this in ajax form. So you don't have to write the code to query the database, parse, convert, etc... on 300 objects on your map. Openlayers will render the latest WFS data on your Geoserver which is pointed to PostGIS. You would save yourself a lot of time and effort reinventing that wheel. Openlayers WFS protocol can be set to query based on your viewport on a temporal filter.

Though features don't perform well when there are a lot of them. 300 might be pushing it. If you see that performance is an issue, you can easily switch to using WMS (only if you have Geoserver or Mapserver). You can also use a cluster strategy to minimize un necessary features on your map.

[GIS] Markers on openlayers openstreetmap

You make mistake in loadMarkers function:

 if(jsonData.markers[i].limpio == 0)
     var icon = new OpenLayers.Icon('redMarker.png',size,offset);   
 if(jsonData.markers[i].limpio == 1)
     var icon = new OpenLayers.Icon('greenMarker.png',size,offset);

After that icon variable is undefined. You should explode this variable before if statement

var icon;
if(jsonData.markers[i].limpio == 0)
     icon = new OpenLayers.Icon('redMarker.png',size,offset);   
else
     icon = new OpenLayers.Icon('greenMarker.png',size,offset);

Probably this is why you can't display your markers. For refreshing markers better is setInterval function than setTimeout. This is sample: setInterval

edit:

In jQuery library you can call:

$.ajax({
  url: "jsonZona.php?zona=".selectBox.value
}).done(function() { 
  // Function to create markers, same as before
});

Best Answer

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