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Android example source code file (Instance.java)

This example Android source code file (Instance.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" TM.

Java - Android tags/keywords

gesture, instance, orientations, patch_sample_size, sequence_sample_size, string

The Instance.java Android example source code

/*
 * Copyright (C) 2008-2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.gesture;


/**
 * An instance represents a sample if the label is available or a query if the
 * label is null.
 */
class Instance {
    private static final int SEQUENCE_SAMPLE_SIZE = 16;

    private static final int PATCH_SAMPLE_SIZE = 16;

    private final static float[] ORIENTATIONS = {
            0, (float) (Math.PI / 4), (float) (Math.PI / 2), (float) (Math.PI * 3 / 4),
            (float) Math.PI, -0, (float) (-Math.PI / 4), (float) (-Math.PI / 2),
            (float) (-Math.PI * 3 / 4), (float) -Math.PI
    };

    // the feature vector
    final float[] vector;

    // the label can be null
    final String label;

    // the id of the instance
    final long id;

    private Instance(long id, float[] sample, String sampleName) {
        this.id = id;
        vector = sample;
        label = sampleName;
    }

    private void normalize() {
        float[] sample = vector;
        float sum = 0;

        int size = sample.length;
        for (int i = 0; i < size; i++) {
            sum += sample[i] * sample[i];
        }

        float magnitude = (float)Math.sqrt(sum);
        for (int i = 0; i < size; i++) {
            sample[i] /= magnitude;
        }
    }

    /**
     * create a learning instance for a single stroke gesture
     * 
     * @param gesture
     * @param label
     * @return the instance
     */
    static Instance createInstance(int sequenceType, int orientationType, Gesture gesture, String label) {
        float[] pts;
        Instance instance;
        if (sequenceType == GestureStore.SEQUENCE_SENSITIVE) {
            pts = temporalSampler(orientationType, gesture);
            instance = new Instance(gesture.getID(), pts, label);
            instance.normalize();
        } else {
            pts = spatialSampler(gesture);
            instance = new Instance(gesture.getID(), pts, label);
        }
        return instance;
    }

    private static float[] spatialSampler(Gesture gesture) {
        return GestureUtils.spatialSampling(gesture, PATCH_SAMPLE_SIZE, false);
    }

    private static float[] temporalSampler(int orientationType, Gesture gesture) {
        float[] pts = GestureUtils.temporalSampling(gesture.getStrokes().get(0),
                SEQUENCE_SAMPLE_SIZE);
        float[] center = GestureUtils.computeCentroid(pts);
        float orientation = (float)Math.atan2(pts[1] - center[1], pts[0] - center[0]);

        float adjustment = -orientation;
        if (orientationType != GestureStore.ORIENTATION_INVARIANT) {
            int count = ORIENTATIONS.length;
            for (int i = 0; i < count; i++) {
                float delta = ORIENTATIONS[i] - orientation;
                if (Math.abs(delta) < Math.abs(adjustment)) {
                    adjustment = delta;
                }
            }
        }

        GestureUtils.translate(pts, -center[0], -center[1]);
        GestureUtils.rotate(pts, adjustment);

        return pts;
    }

}

Other Android examples (source code examples)

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