1 | /* Copyright (c) 2006-2010 by OpenLayers Contributors (see authors.txt for |
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2 | * full list of contributors). Published under the Clear BSD license. |
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3 | * See http://svn.openlayers.org/trunk/openlayers/license.txt for the |
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4 | * full text of the license. */ |
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5 | |
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6 | /** |
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7 | * @requires OpenLayers/Strategy.js |
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8 | */ |
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9 | |
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10 | /** |
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11 | * Class: OpenLayers.Strategy.Cluster |
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12 | * Strategy for vector feature clustering. |
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13 | * |
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14 | * Inherits from: |
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15 | * - <OpenLayers.Strategy> |
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16 | */ |
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17 | OpenLayers.Strategy.Cluster = OpenLayers.Class(OpenLayers.Strategy, { |
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18 | |
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19 | /** |
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20 | * APIProperty: distance |
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21 | * {Integer} Pixel distance between features that should be considered a |
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22 | * single cluster. Default is 20 pixels. |
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23 | */ |
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24 | distance: 20, |
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25 | |
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26 | /** |
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27 | * APIProperty: threshold |
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28 | * {Integer} Optional threshold below which original features will be |
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29 | * added to the layer instead of clusters. For example, a threshold |
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30 | * of 3 would mean that any time there are 2 or fewer features in |
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31 | * a cluster, those features will be added directly to the layer instead |
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32 | * of a cluster representing those features. Default is null (which is |
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33 | * equivalent to 1 - meaning that clusters may contain just one feature). |
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34 | */ |
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35 | threshold: null, |
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36 | |
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37 | /** |
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38 | * Property: features |
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39 | * {Array(<OpenLayers.Feature.Vector>)} Cached features. |
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40 | */ |
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41 | features: null, |
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42 | |
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43 | /** |
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44 | * Property: clusters |
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45 | * {Array(<OpenLayers.Feature.Vector>)} Calculated clusters. |
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46 | */ |
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47 | clusters: null, |
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48 | |
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49 | /** |
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50 | * Property: clustering |
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51 | * {Boolean} The strategy is currently clustering features. |
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52 | */ |
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53 | clustering: false, |
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54 | |
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55 | /** |
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56 | * Property: resolution |
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57 | * {Float} The resolution (map units per pixel) of the current cluster set. |
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58 | */ |
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59 | resolution: null, |
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60 | |
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61 | /** |
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62 | * Constructor: OpenLayers.Strategy.Cluster |
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63 | * Create a new clustering strategy. |
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64 | * |
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65 | * Parameters: |
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66 | * options - {Object} Optional object whose properties will be set on the |
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67 | * instance. |
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68 | */ |
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69 | initialize: function(options) { |
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70 | OpenLayers.Strategy.prototype.initialize.apply(this, [options]); |
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71 | }, |
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72 | |
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73 | /** |
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74 | * APIMethod: activate |
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75 | * Activate the strategy. Register any listeners, do appropriate setup. |
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76 | * |
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77 | * Returns: |
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78 | * {Boolean} The strategy was successfully activated. |
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79 | */ |
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80 | activate: function() { |
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81 | var activated = OpenLayers.Strategy.prototype.activate.call(this); |
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82 | if(activated) { |
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83 | this.layer.events.on({ |
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84 | "beforefeaturesadded": this.cacheFeatures, |
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85 | "moveend": this.cluster, |
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86 | scope: this |
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87 | }); |
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88 | } |
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89 | return activated; |
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90 | }, |
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91 | |
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92 | /** |
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93 | * APIMethod: deactivate |
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94 | * Deactivate the strategy. Unregister any listeners, do appropriate |
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95 | * tear-down. |
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96 | * |
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97 | * Returns: |
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98 | * {Boolean} The strategy was successfully deactivated. |
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99 | */ |
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100 | deactivate: function() { |
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101 | var deactivated = OpenLayers.Strategy.prototype.deactivate.call(this); |
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102 | if(deactivated) { |
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103 | this.clearCache(); |
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104 | this.layer.events.un({ |
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105 | "beforefeaturesadded": this.cacheFeatures, |
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106 | "moveend": this.cluster, |
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107 | scope: this |
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108 | }); |
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109 | } |
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110 | return deactivated; |
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111 | }, |
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112 | |
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113 | /** |
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114 | * Method: cacheFeatures |
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115 | * Cache features before they are added to the layer. |
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116 | * |
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117 | * Parameters: |
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118 | * event - {Object} The event that this was listening for. This will come |
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119 | * with a batch of features to be clustered. |
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120 | * |
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121 | * Returns: |
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122 | * {Boolean} False to stop features from being added to the layer. |
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123 | */ |
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124 | cacheFeatures: function(event) { |
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125 | var propagate = true; |
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126 | if(!this.clustering) { |
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127 | this.clearCache(); |
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128 | this.features = event.features; |
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129 | this.cluster(); |
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130 | propagate = false; |
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131 | } |
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132 | return propagate; |
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133 | }, |
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134 | |
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135 | /** |
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136 | * Method: clearCache |
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137 | * Clear out the cached features. |
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138 | */ |
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139 | clearCache: function() { |
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140 | this.features = null; |
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141 | }, |
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142 | |
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143 | /** |
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144 | * Method: cluster |
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145 | * Cluster features based on some threshold distance. |
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146 | * |
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147 | * Parameters: |
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148 | * event - {Object} The event received when cluster is called as a |
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149 | * result of a moveend event. |
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150 | */ |
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151 | cluster: function(event) { |
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152 | if((!event || event.zoomChanged) && this.features) { |
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153 | var resolution = this.layer.map.getResolution(); |
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154 | if(resolution != this.resolution || !this.clustersExist()) { |
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155 | this.resolution = resolution; |
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156 | var clusters = []; |
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157 | var feature, clustered, cluster; |
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158 | for(var i=0; i<this.features.length; ++i) { |
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159 | feature = this.features[i]; |
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160 | if(feature.geometry) { |
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161 | clustered = false; |
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162 | for(var j=clusters.length-1; j>=0; --j) { |
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163 | cluster = clusters[j]; |
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164 | if(this.shouldCluster(cluster, feature)) { |
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165 | this.addToCluster(cluster, feature); |
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166 | clustered = true; |
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167 | break; |
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168 | } |
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169 | } |
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170 | if(!clustered) { |
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171 | clusters.push(this.createCluster(this.features[i])); |
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172 | } |
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173 | } |
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174 | } |
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175 | this.layer.removeAllFeatures(); |
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176 | if(clusters.length > 0) { |
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177 | if(this.threshold > 1) { |
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178 | var clone = clusters.slice(); |
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179 | clusters = []; |
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180 | var candidate; |
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181 | for(var i=0, len=clone.length; i<len; ++i) { |
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182 | candidate = clone[i]; |
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183 | if(candidate.attributes.count < this.threshold) { |
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184 | Array.prototype.push.apply(clusters, candidate.cluster); |
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185 | } else { |
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186 | clusters.push(candidate); |
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187 | } |
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188 | } |
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189 | } |
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190 | this.clustering = true; |
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191 | // A legitimate feature addition could occur during this |
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192 | // addFeatures call. For clustering to behave well, features |
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193 | // should be removed from a layer before requesting a new batch. |
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194 | this.layer.addFeatures(clusters); |
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195 | this.clustering = false; |
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196 | } |
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197 | this.clusters = clusters; |
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198 | } |
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199 | } |
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200 | }, |
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201 | |
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202 | /** |
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203 | * Method: clustersExist |
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204 | * Determine whether calculated clusters are already on the layer. |
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205 | * |
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206 | * Returns: |
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207 | * {Boolean} The calculated clusters are already on the layer. |
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208 | */ |
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209 | clustersExist: function() { |
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210 | var exist = false; |
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211 | if(this.clusters && this.clusters.length > 0 && |
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212 | this.clusters.length == this.layer.features.length) { |
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213 | exist = true; |
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214 | for(var i=0; i<this.clusters.length; ++i) { |
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215 | if(this.clusters[i] != this.layer.features[i]) { |
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216 | exist = false; |
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217 | break; |
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218 | } |
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219 | } |
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220 | } |
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221 | return exist; |
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222 | }, |
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223 | |
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224 | /** |
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225 | * Method: shouldCluster |
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226 | * Determine whether to include a feature in a given cluster. |
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227 | * |
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228 | * Parameters: |
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229 | * cluster - {<OpenLayers.Feature.Vector>} A cluster. |
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230 | * feature - {<OpenLayers.Feature.Vector>} A feature. |
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231 | * |
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232 | * Returns: |
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233 | * {Boolean} The feature should be included in the cluster. |
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234 | */ |
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235 | shouldCluster: function(cluster, feature) { |
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236 | var cc = cluster.geometry.getBounds().getCenterLonLat(); |
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237 | var fc = feature.geometry.getBounds().getCenterLonLat(); |
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238 | var distance = ( |
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239 | Math.sqrt( |
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240 | Math.pow((cc.lon - fc.lon), 2) + Math.pow((cc.lat - fc.lat), 2) |
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241 | ) / this.resolution |
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242 | ); |
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243 | return (distance <= this.distance); |
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244 | }, |
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245 | |
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246 | /** |
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247 | * Method: addToCluster |
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248 | * Add a feature to a cluster. |
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249 | * |
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250 | * Parameters: |
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251 | * cluster - {<OpenLayers.Feature.Vector>} A cluster. |
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252 | * feature - {<OpenLayers.Feature.Vector>} A feature. |
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253 | */ |
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254 | addToCluster: function(cluster, feature) { |
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255 | cluster.cluster.push(feature); |
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256 | cluster.attributes.count += 1; |
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257 | }, |
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258 | |
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259 | /** |
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260 | * Method: createCluster |
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261 | * Given a feature, create a cluster. |
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262 | * |
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263 | * Parameters: |
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264 | * feature - {<OpenLayers.Feature.Vector>} |
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265 | * |
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266 | * Returns: |
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267 | * {<OpenLayers.Feature.Vector>} A cluster. |
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268 | */ |
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269 | createCluster: function(feature) { |
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270 | var center = feature.geometry.getBounds().getCenterLonLat(); |
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271 | var cluster = new OpenLayers.Feature.Vector( |
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272 | new OpenLayers.Geometry.Point(center.lon, center.lat), |
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273 | {count: 1} |
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274 | ); |
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275 | cluster.cluster = [feature]; |
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276 | return cluster; |
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277 | }, |
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278 | |
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279 | CLASS_NAME: "OpenLayers.Strategy.Cluster" |
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280 | }); |
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