处理测量结果#

本主题告诉您如何处理 Basler blaze 相机的测量结果。

概述#

Basler blaze 相机测量每个传感器像素的光传播距离。

使用这些距离，相机会在右旋坐标系中计算每个传感器像素的 x、y、z 坐标。坐标系的原点位于相机的光学中心，该中心位于相机外壳内。y 轴指向下方，z 轴指向远离相机的方向。

相机以深度图或点云的形式提供 3D 信息，取决于像素格式。在深度图中，z 坐标被编码为 16 位灰度值。如下所示，可以从灰度值中计算出所有 3D 坐标值。点云以浮点数的形式包含每个传感器像素的 x、y、z 3D 坐标。单位是 mm。

If there is no valid depth information for a sensor pixel (e.g., due to outlier removal or insufficient light, i.e., light that is not strong enough to pass the confidence threshold), the corresponding values in a depth map or a point cloud are set to the value defined by the Scan3dInvalidDataValue parameter (default setting is 0).

处理深度图#

深度图由 16 位灰度值组成。对于每个传感器像素，相机会将 z 坐标值转换为灰度值，并将其存储在深度图中。

In combination with the camera's calibration data provided by the Scan3dCoordinateScale, Scan3dPrincipalPointU, Scan3dPrincipalPointV, and Scan3dFocalLength parameters, complete 3D information can be retrieved from a depth map.

请参阅 GrabDepthMap C++ 示例，了解如何配置相机以发送深度图以及如何访问深度图数据。

从 2D 深度图计算 3D 坐标#

要将深度图的 16 位灰度值转换为以 mm 为单位的 z 坐标，请使用以下公式：

z [mm] = gray2mm * g

其中：

g = gray value from the depth map

gray2mm = value of the Scan3dCoordinateScale parameter

要计算 x 和 y 坐标，请使用以下公式：

x [mm] = (u-cx) * z / f

y [mm] = (v-cy) * z / f

其中：

(u,v) = column and row in the depth map

f = value of the Scan3dFocalLength parameter, i.e., the focal length of the camera's lens

(cx,cy) = values of the Scan3dPrincipalPointU and Scan3dPrincipalPointV parameters, i.e., the principal point

C++ 示例代码#

    // Enable depth maps by enabling the Range component and setting the appropriate pixel format.
    camera.ComponentSelector.SetValue(ComponentSelector_Range);
    camera.ComponentEnable.SetValue(true);
    camera.PixelFormat.SetValue(PixelFormat_Coord3D_C16);

    // Query the conversion factor required to convert gray values to distances:
    // Choose the z axis first...
    camera.Scan3dCoordinateSelector.SetValue(Scan3dCoordinateSelector_CoordinateC);
    // ... then retrieve the conversion factor.
    const auto gray2mm = camera.Scan3dCoordinateScale.GetValue();

    // Configure the gray value used for indicating missing depth data.
    // Note: Before setting the value, the Scan3dCoordinateSelector parameter must be set to the axis the
    // value is to be configured for, in this case the z axis. This means that Scan3dCoordianteSelector must be set
    // to "CoordinateC". This has already been done a few lines above.
    camera.Scan3dInvalidDataValue.SetValue((double)missingDepth);

    // Retrieve calibration data from the camera.
    const auto cx = camera.Scan3dPrincipalPointU.GetValue();
    const auto cy = camera.Scan3dPrincipalPointV.GetValue();
    const auto f = camera.Scan3dFocalLength.GetValue();

    // ....

    // Access the data.
    const auto container = ptrGrabResult->GetDataContainer();
    const auto rangeComponent = container.GetDataComponent(0);
    const auto width = rangeComponent.GetWidth();
    const auto height = rangeComponent.GetHeight();

    // Calculate coordinates for pixel (u,v).
    const uint16_t g = ((uint16_t*)rangeComponent.GetData())[u + v * width];
    const double z = g * gray2mm;
    const double x = (u - cx) * z / f;
    const double y = (v - cy) * z / f;

处理已保存的深度图#

对于使用 blaze 旧版 SDK、pylon SDK 或 blaze ROS 驱动程序获得的深度图，您必须使用以下公式：

Distance Measured [mm] = Pixel_Value x Scan3dCoordinateScale[C]

对于使用 blaze Viewer 保存的深度图，请使用以下公式：

Distance Measured [mm] = DepthMin_parameter + (Pixel_Value x (DepthMax_Parameter - DepthMin_parameter)) / 65535

处理点云#

由于点云由相机坐标系内的 x、y、z 坐标三元组组成，因此无需进一步处理即可从点云中提取 3D 信息。

有关如何配置用于发送点云的相机以及如何访问数据的信息，请参阅 FirstSample C++ 示例。

如果除了点云之外还需要深度图，请参考 ConvertPointCloud2DepthMap C++ 示例，该示例说明如何从点云计算灰度和 RGB 深度图。

将坐标系的原点移动到相机外壳的前部#

The camera's coordinate system's origin is located in the camera's optical center which is inside the camera housing. If you prefer coordinates in a coordinate system which is located at the camera's front of the housing, i.e., which is translated along the z axis, a constant, device-specific offset has to be subtracted from the z coordinates. The required offset can be retrieved from the camera by getting the value of the ZOffsetOriginToCameraFront parameter:

const double offset = camera.ZOffsetOriginToCameraFront.GetValue();

如果 (x,y,z) 是相机坐标系中某个点的坐标，则沿 z 轴移到相机坐标系外壳前部的坐标系中对应坐标 (x',y',z') 可以使用以下公式确定：

x' = x

y' = y

z' = z - offset

计算距离#

Given a point's coordinates (x,y,z) in mm, the distance of that point to the camera's optical center can be calculated using the following formula:

d = sqrt( xx + yy + z*z )

The distance d' to the front of the camera's housing can be calculated as follows:

z' = z - offset

d' = sqrt( xx + yy + z'*z')

将深度信息可视化为 RGB 图像#

您可以使用以下方案针对彩虹颜色映射，根据 z 坐标或距离值计算 RGB 值。这对于更好地可视化数据很有用。

First, a depth value from the [minDepth..maxDepth] value range is converted into a 10-bit value. This 10-bit depth value is mapped to 4 color ranges where each range has a resolution of 8 bits.

minDepth and maxDepth = values of the DepthMin and DepthMax parameters, i.e., the camera's current depth ROI

In the following code snippet, depth is either a z value or a distance value in mm.

const int minDepth = (int)m_camera.DepthMin.GetValue();
const int maxDepth = (int)m_camera.DepthMax.GetValue();

const double scale = 65536.0 / (maxDepth - minDepth);

for each pixel {
    // Set depth either to the corresponding z value or
    // a distance value calculated from the z value.
    // Clip depth if required.
    if (depth < minDepth)
        depth = minDepth;
    else if (depth > maxDepth)
        depth = maxDepth;
    // Compute RGB values.
    const uint16_t g = (uint16_t)((depth - minDepth) * scale);
    const uint16_t val = g >> 6 & 0xff;
    const uint16_t sel = g >> 14;
    uint32_t res = val << 8 | 0xff;
    if (sel & 0x01)
    {
        res = (~res) >> 8 & 0xffff;
    }
    if (sel & 0x02)
    {
        res = res << 8;
    }
    const uint8_t r = res & 0xff;
    res = res >> 8;
    const uint8_t g = res & 0xff;
    res = res >> 8;
    const uint8_t b = res & 0xff;
}