Question

我想对ARKit会话期间在单个帧中找到的每个检测到的特征点进行一些处理。如何迭代每个检测到的特征点，并获得它们的世界坐标？

我使用Swift，但Objective-C答案也会很好。

Answer 1

编辑：在Xcode 9.0 GM（及更高版本）中，points是float3向量的Swift数组，因此您可以像任何其他Swift数组一样迭代它：< / p>

for point in frame.rawFeaturePoints.points { 
    ...
}

或者：

frame.rawFeaturePoints.points.map { point in 
    ... 
}

或者您最喜欢的阵列/收集算法。

在各种Xcode 9.x测试版中，此属性的Swift Array版本不可用。因此，您必须处理underlying ObjC property，它导入Swift为UnsafePointer，您无法轻易迭代。（因此OP的原始问题。）

如果该错误重新出现（或者您在其他地方遇到类似的问题），您可以这样做：

for index in 0..<frame.rawFeaturePoints.count {
    let point = frame.rawFeaturePoints.points[index]
    // do something with point
}

Answer 2

由于我花了一段时间才得到一个工作样本，看看如何获得特征点的渲染，这里有一个完整的工作示例：

SCNNode *ARPointCloudNode = nil;

- (void)session:(ARSession *)session didUpdateFrame:(ARFrame *)frame API_AVAILABLE(ios(11.0));
{

    NSInteger pointCount = frame.rawFeaturePoints.count;
    if (pointCount) {
        // We want a root node to work in, it's going to hold the all of the represented spheres
        // that come together to make the point cloud
        if (!ARPointCloudNode) {
            ARPointCloudNode = [SCNNode node];
            [self.sceneView.scene.rootNode addChildNode:ARPointCloudNode];
        }

        // It's going to need some colour
        SCNMaterial *whiteMaterial = [SCNMaterial material];
        whiteMaterial.diffuse.contents = [UIColor whiteColor];
        whiteMaterial.locksAmbientWithDiffuse = YES;

        // Remove the old point clouds (this happens per-frame
        for (SCNNode *child in ARPointCloudNode.childNodes) {
            [child removeFromParentNode];
        }

        // Use the frames point cloud to create a set of SCNSpheres
        // which live at the feature point in the AR world
        for (NSInteger i = 0; i < pointCount; i++) {
            vector_float3 point = frame.rawFeaturePoints.points[i];
            SCNVector3 vector = SCNVector3Make(point[0], point[1], point[2]);

            SCNSphere *pointSphere = [SCNSphere sphereWithRadius:0.001];
            pointSphere.materials = @[whiteMaterial];

            SCNNode *pointNode = [SCNNode nodeWithGeometry:pointSphere];
            pointNode.position = vector;

            [ARPointCloudNode addChildNode:pointNode];
        }
    }
}

ARKit：你如何迭代所有检测到的特征点？

2 个答案: