在Wikitude中裁剪图像

我正在Wikitude AR SDK中进行简单的图像识别 . 我正在使用Javascript SDK并启动了示例项目“01_ImageRecognition_1_ImageOnTarget” . 代码是这样的：

var World = {
    loaded: false,

    init: function initFn() {
        this.createOverlays();
    },

    createOverlays: function createOverlaysFn() {
        /*
            First an AR.ImageTracker needs to be created in order to start the recognition engine. It is initialized with a AR.TargetCollectionResource specific to the target collection that should be used. Optional parameters are passed as object in the last argument. In this case a callback function for the onTargetsLoaded trigger is set. Once the tracker loaded all its target images, the function worldLoaded() is called.

            Important: If you replace the tracker file with your own, make sure to change the target name accordingly.
            Use a specific target name to respond only to a certain target or use a wildcard to respond to any or a certain group of targets.
        */
        this.targetCollectionResource = new AR.TargetCollectionResource("assets/bp2.wtc", {
        });

        this.tracker = new AR.ImageTracker(this.targetCollectionResource, {
            onTargetsLoaded: this.worldLoaded
        });

        /*
            The next step is to create the augmentation. In this example an image resource is created and passed to the 
            AR.ImageDrawable. A drawable is a visual component that can be connected to an IR target (AR.ImageTrackable) 
            or a geolocated object (AR.GeoObject). The AR.ImageDrawable is initialized by the image and its size. 
            Optional parameters allow for position it relative to the recognized target.
        */

        /* Create overlay for page one */
        var imgOne = new AR.ImageResource("assets/imageOne.png");
        var overlayOne = new AR.ImageDrawable(imgOne, 1, {
            translate: {
                x:-0.15
            }

        });

        /*
            The last line combines everything by creating an AR.ImageTrackable with the previously created tracker, the name of the image target and the drawable that should augment the recognized image.
            Please note that in this case the target name is a wildcard. Wildcards can be used to respond to any target defined in the target collection. If you want to respond to a certain target only for a particular AR.ImageTrackable simply provide the target name as specified in the target collection.
        */
        var pageOne = new AR.ImageTrackable(this.tracker, "*", {
            drawables: {
                cam: overlayOne
            }
        });
    },

    worldLoaded: function worldLoadedFn() {

        var cssDivLeft = " style='display: table-cell;vertical-align: middle; text-align: right; width: 50%; padding-right: 15px;'";
        var cssDivRight = " style='display: table-cell;vertical-align: middle; text-align: left;'";
        document.getElementById('loadingMessage').innerHTML =
            "<div" + cssDivLeft + ">Scan Target &#35;1 (surfer):</div>" +
            "<div" + cssDivRight + "><img src='assets/bp.png'></img></div>";

        // Remove Scan target message after 10 sec.
        setTimeout(function() {
            var e = document.getElementById('loadingMessage');
            e.parentElement.removeChild(e);
        }, 10000);
    }
};
World.init();

我的目的是裁剪被识别的拍摄图像 . 我在Wikitude论坛上问过，但没有人引导我，我找不到相关的文档 . 我希望有人在这里帮助我 .