用奥比深度相机扫描一个非常平的平面，为什么深度值会出现厘米级的误差？

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用奥比深度相机扫描一个非常平的平面，出现了4个毫米的误差。

这个误差是如何产生的？是应为相机平面与我给定的平面存在倾斜造成的？还是相机本身精度造成的？

运算代码如下：

#include <iostream>
#include <vector>
#include "OpenNI.h"
#include "OniSampleUtilities.h"using namespace openni;
using namespace std;#define MIN_DISTANCE 20  //单位毫米
#define MAX_DISTANCE 1200 //单位毫米
#define RESOULTION_X 640.0  //标定时的分辨率
#define RESOULTION_Y 480.0  //标定时的分辨率#define MAX_FRAME_COUNT 50typedef struct SPoint
{float x, y, z;SPoint(float u = 0.0f, float v = 0.0f, float w = 0.0f): x(u), y(v), z(w) { }
} Point;typedef struct xnIntrinsic_Params
{xnIntrinsic_Params() :c_x(320.0), c_y(240.0), f_x(480.0), f_y(480.0){}xnIntrinsic_Params(float c_x_, float c_y_, float f_x_, float f_y_) :c_x(c_x_), c_y(c_y_), f_x(f_x_),f_y(f_y_){}float c_x; //u轴上的归一化焦距float c_y; //v轴上的归一化焦距float f_x; //主点x坐标float f_y; //主点y坐标
}xIntrinsic_Params;xIntrinsic_Params g_IntrinsicParam; //存储相机内参的全局变量void getCameraParams(openni::Device& Device, xIntrinsic_Params& IrParam)
{OBCameraParams cameraParam;int dataSize = sizeof(cameraParam);memset(&cameraParam, 0, sizeof(cameraParam));openni::Status rc = Device.getProperty(openni::OBEXTENSION_ID_CAM_PARAMS, (uint8_t *)&cameraParam, &dataSize);if (rc != openni::STATUS_OK){std::cout << "Error:" << openni::OpenNI::getExtendedError() << std::endl;return;}IrParam.f_x = cameraParam.l_intr_p[0]; //u轴上的归一化焦距IrParam.f_y = cameraParam.l_intr_p[1]; //v轴上的归一化焦距IrParam.c_x = cameraParam.l_intr_p[2]; //主点x坐标IrParam.c_y = cameraParam.l_intr_p[3]; //主点y坐标
}void convertDepthToPointCloud(const uint16_t *pDepth, int width, int height, int middleIndex)
{if (NULL == pDepth){printf("depth frame is NULL!");return;}//分辨率缩放，这里假设标定时的分辨率分RESOULTION_X，RESOULTION_Yfloat fdx = g_IntrinsicParam.f_x * ((float)(width) / RESOULTION_X);float fdy = g_IntrinsicParam.f_y * ((float)(height) / RESOULTION_Y);float u0  = g_IntrinsicParam.c_x * ((float)(width) / RESOULTION_X);float v0  = g_IntrinsicParam.c_y * ((float)(height) / RESOULTION_Y);// 得到被扫描平面中心点的坐标SPoint midPoint(pDepth[middleIndex] * (width / 2 - u0) / fdx, pDepth[middleIndex] * ((height + 1) / 2 - v0) / fdy, pDepth[middleIndex]);vector<Point> points;uint16_t max_depth = MAX_DISTANCE;uint16_t min_depth = MIN_DISTANCE;float x, y, z;for (int v = 0; v < height; ++v){for (int u = 0; u < width; ++u){uint16_t depth = pDepth[v * width + u];if (depth <= 0 || depth < min_depth || depth > max_depth)continue;float tx = (u - u0) / fdx;float ty = (v - v0) / fdy;// 将中心点定义为世界坐标系的原点x = depth * tx - midPoint.x, y = depth * ty - midPoint.y, z = depth;if (x + 100.0f <= 0.001f || x - 100.0f >= 0.001f) continue;  // 滤波if (y + 100.0f <= 0.001f || y - 100.0f >= 0.001f) continue;points.push_back(SPoint(x, y, z));}}for (size_t i = 0; i < points.size(); ++i)cout << points[i].x << " " << points[i].y << " " <<points[i].z << endl;
}int g_imageCount = 0;void analyzeFrame(const VideoFrameRef& frame)
{DepthPixel* pDepth;g_imageCount++;if (MAX_FRAME_COUNT < g_imageCount){return;}//int middleIndex = (frame.getHeight() + 1)*frame.getWidth() / 2;switch (frame.getVideoMode().getPixelFormat()){case PIXEL_FORMAT_DEPTH_1_MM:pDepth = (DepthPixel*)frame.getData();//printf("[%08llu] %8d\n", (long long)frame.getTimestamp(),//    pDepth[middleIndex]);//将深度数据转换为点云并保存成ply文件，每帧深度数据对应一个ply文件convertDepthToPointCloud(pDepth, frame.getWidth(), frame.getHeight(), (frame.getHeight() + 1) * frame.getWidth() / 2);break;default:printf("Unknown format\n");}
}class PrintCallback : public VideoStream::NewFrameListener
{
public:void onNewFrame(VideoStream& stream){stream.readFrame(&m_frame);analyzeFrame(m_frame);}
private:VideoFrameRef m_frame;
};int main(int argc, char* argv[])
{//initialize openNI sdkStatus rc = OpenNI::initialize();if (rc != STATUS_OK){printf("Initialize failed\n%s\n", OpenNI::getExtendedError());return 1;}//open deivceDevice device;rc = device.open(ANY_DEVICE);if (rc != STATUS_OK){printf("Couldn't open device\n%s\n", OpenNI::getExtendedError());return 2;}VideoStream depth;//create depth streamif (device.getSensorInfo(SENSOR_DEPTH) != NULL){rc = depth.create(device, SENSOR_DEPTH);if (rc != STATUS_OK){printf("Couldn't create depth stream\n%s\n", OpenNI::getExtendedError());}}//start depth streamrc = depth.start();if (rc != STATUS_OK){printf("Couldn't start the depth stream\n%s\n", OpenNI::getExtendedError());}PrintCallback depthPrinter;// Register frame listenerdepth.addNewFrameListener(&depthPrinter);//get intrinsic parameter from devicegetCameraParams(device, g_IntrinsicParam);// Wait while we're getting frames through the printerwhile (MAX_FRAME_COUNT > g_imageCount){Sleep(100);}depth.removeNewFrameListener(&depthPrinter);//stop depth streamdepth.stop();//destroy depth streamdepth.destroy();//close devicedevice.close();//shutdown OpenNIOpenNI::shutdown();return 0;
}