How to configure how close together features need to be to form a cluster in openlayers3 - openlayers-3

Question

Is there a parameter to set a minimum radius for features to cluster? - so that when a set of points or features are within some minimum distance, they form a cluster, otherwise not?
ol.source.Cluster() has two parameters that look promising, but don't seem to work as expected.
distance: Minimum distance in pixels between clusters. Default is 20.
extent: An array of numbers representing an extent: [minx, miny,
maxx, maxy].

Answer 1

Not quite sure what "but don't seem to work as expected." means?? How does it not work as expected??
distance property of ol.source.Cluster tells the layer when to group objects based on the distance set. It can be changed when creating the cluster layer. For example:
var locationSource = new ol.source.Vector({
url: loc_url,
format: new ol.format.GeoJSON({
defaultDataProjection :'EPSG:3857'
}),
loader: vectorLoader,
strategy: ol.loadingstrategy.all
});
var LOCclusterSource = new ol.source.Cluster({
distance: 5,
source: locationSource
});
I usually change the distance object until I find the desired distance so group/cluster object look right on the map.
The radius of a group object on a map layer can be change via a style function for the map layer. Many example of style functions exist here on stack.
Here is a hacked up example that I use to increase the radius of cluster/group objects on the map layer so it's visually obvious that it is a group/cluster object:
NOTE: You can have different shapes on the same layer too using a style function. https://openlayers.org/en/latest/examples/regularshape.html
// Location Map Layer Properties
var locLyrProps = {
"radius": 8,
"CORadius": 12,
"groupRadius": 10,
"borderWidth": 2,
"color": [0, 0, 0, 0.5],
"txtMaxRes": 20,
"txtOffsetY": -20
};
var styleFunction = function() {
return function(feature,resolution) {
var style;
var props = locLyrProps;
var radius;
var lyrTyp;
var gotGroup = false;
var features = feature.get('features');
if (features.length == 1) { //Individual map object because length = 1
style = new ol.style.Style({ //Square layer object
image: new ol.style.RegularShape({
radius: radius,
points: 4,
angle: Math.PI / 4,
fill: createFillStyle(feature),
stroke: createStrokeStyle(feature, resolution)
}),
text: createTextStyle(feature, resolution)
});
} else {
var rad = props.radius;
if (features.length > 1) { //If cluster/group of features increase radius of group object so group objects stand out a bit
rad = props.groupRadius; //If cluster/group object is found, set cluster/group radius for it
gotGroup = true;
}
console.log('circle radius: ' + rad);
style = new ol.style.Style({
image: new ol.style.Circle({
radius: rad,
fill: createFillStyle(feature),
stroke: createStrokeStyle(feature, resolution, gotGroup)
}),
text: createTextStyle(feature, resolution, props, gotGroup)
});
}
return [style];
};
};