Table of Contents for
Mastering OpenLayers 3

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Mastering OpenLayers 3 by Gábor Farkas Published by Packt Publishing, 2016
  1. Cover
  2. Table of Contents
  3. Mastering OpenLayers 3
  4. Mastering OpenLayers 3
  5. Credits
  6. About the Author
  7. About the Reviewer
  8. www.PacktPub.com
  9. Preface
  10. What you need for this book
  11. Who this book is for
  12. Conventions
  13. Reader feedback
  14. Customer support
  15. 1. Creating Simple Maps with OpenLayers 3
  16. Structure of OpenLayers 3
  17. Building the layout
  18. Using the API documentation
  19. Debugging the code
  20. Summary
  21. 2. Applying Custom Styles
  22. Customizing the default appearance
  23. Styling vector layers
  24. Customizing the appearance with JavaScript
  25. Creating a WebGIS client layout
  26. Summary
  27. 3. Working with Layers
  28. Building a layer tree
  29. Adding layers dynamically
  30. Adding vector layers with the File API
  31. Adding vector layers with a library
  32. Removing layers dynamically
  33. Changing layer attributes
  34. Changing the layer order with the Drag and Drop API
  35. Clearing the message bar
  36. Summary
  37. 4. Using Vector Data
  38. Accessing attributes
  39. Setting attributes
  40. Validating attributes
  41. Creating thematic layers
  42. Saving vector data
  43. Saving with WFS-T
  44. Modifying the geometry
  45. Summary
  46. 5. Creating Responsive Applications with Interactions and Controls
  47. Building the toolbar
  48. Mapping interactions to controls
  49. Building a set of feature selection controls
  50. Adding new vector layers
  51. Building a set of drawing tools
  52. Modifying and snapping to features
  53. Creating new interactions
  54. Building a measuring control
  55. Summary
  56. 6. Controlling the Map – View and Projection
  57. Customizing a view
  58. Constraining a view
  59. Creating a navigation history
  60. Working with extents
  61. Rotating a view
  62. Changing the map's projection
  63. Creating custom animations
  64. Summary
  65. 7. Mastering Renderers
  66. Using different renderers
  67. Creating a WebGL map
  68. Drawing lines and polygons with WebGL
  69. Blending layers
  70. Clipping layers
  71. Exporting a map
  72. Creating a raster calculator
  73. Creating a convolution matrix
  74. Clipping a layer with WebGL
  75. Summary
  76. 8. OpenLayers 3 for Mobile
  77. Responsive styling with CSS
  78. Generating geocaches
  79. Adding device-dependent controls
  80. Vectorizing the mobile version
  81. Making the mobile application interactive
  82. Summary
  83. 9. Tools of the Trade – Integrating Third-Party Applications
  84. Exporting a QGIS project
  85. Importing shapefiles
  86. Spatial analysis with Turf
  87. Spatial analysis with JSTS
  88. 3D rendering with Cesium
  89. Summary
  90. 10. Compiling Custom Builds with Closure
  91. Configuring Node JS
  92. Compiling OpenLayers 3
  93. Bundling an application with OpenLayers 3
  94. Extending OpenLayers 3
  95. Creating rich documentation with JSDoc
  96. Summary
  97. Index

Modifying and snapping to features

In this example, called ch05_modify, we will customize the remaining feature editing interactions before we go on and create our own. Firstly, we create some further CSS rules for our new controls:

.toolbar .ol-modifyfeat button {
    background-image: url(../../res/button_modifyfeat.png);
}
.toolbar .ol-snap button {
    background-image: url(../../res/button_snap.png);
}

Extending the method

Now that we have the required rules, we can extend our addEditingToolBar method with two additional interactions. As both the modify and the snap interactions accept a collection of features to work with, we go that way and store the selected layer's features in a new collection object:

toolBar.prototype.addEditingToolBar = function () {
    […]
    this.activeFeatures = new ol.Collection();
    var modifyFeature = new ol.control.Interaction({
        label: ' ',
        tipLabel: 'Modify features',
        className: 'ol-modifyfeat ol-unselectable ol-control',
        interaction: new ol.interaction.Modify({
            features: this.activeFeatures
        })
    }).setDisabled(true);
    this.editingControls.push(modifyFeature);
    var snapFeature = new ol.control.Interaction({
        label: ' ',
        tipLabel: 'Snap to paths, and vertices',
        className: 'ol-snap ol-unselectable ol-control',
        interaction: new ol.interaction.Snap({
            features: this.activeFeatures
        })
    }).setDisabled(true);
    snapFeature.unset('type');
    this.editingControls.push(snapFeature);

We created two new custom controls with two interactions. As the snapping control can be and must be active along another editing control, we manually remove its type attribute before adding it to the toolbar. We also linked our new collection to the interactions, making it possible to dynamically modify the features they will work with. Next, we make sure to correctly update our activeFeatures object on the layer change and add our new controls to the toolbar:

    layertree.selectEventEmitter.on('change', function () {
        […]
            var _this = this;
            setTimeout(function () {
                _this.activeFeatures.clear();
                _this.activeFeatures.extend(layer.getSource().getFeatures());
            }, 0);
        […]
    }, this);     this.addControl(drawPoint).addControl(drawLine).addControl(drawPolygon)
        .addControl(modifyFeature).addControl(snapFeature);
    return this;
};

As creating a copy from our selected layer's features takes some time, rendering our layer tree unresponsive for a few seconds even with a smaller dataset, we make it asynchronous by calling it in a setTimeout function set to zero milliseconds. Note that this method will not speed up our code, but makes our application more responsive.

A responsive application is technically a matter of chunking time-consuming code blocks into smaller and faster ones, and timing their executions when the user doesn't notice. The physical reaction of the human body is significantly slower than visual reaction; thus, by placing the few seconds loading time after the visual feedback with an asynchronous call, the users won't even notice that there was any loading time. Of course, this theorem only applies to small datasets.

Tip

If you have to work with large datasets, this will definitely be a bottleneck of your application. In this case, you can construct vector layers with a new collection object and call the source's getFeaturesCollection method on the layer change, avoiding the need for duplicating features. However, as the inner collection of the interactions cannot be changed, you have to construct a new interaction and remove the old one from the map every time.

Finally, we only have to add every newly created feature to our collection, so the interactions can be applied on them without changing the active layer:

toolBar.prototype.handleEvents = function (interaction, type) {
    […]
    interaction.on('drawend', function (evt) {
        […]
            this.activeFeatures.push(evt.feature);
        […]
};

If you save and load up the example, you can see our new controls in action:

Extending the method