Thursday, March 23, 2017

LiDAR data coordinate readout in Cloud Compare

It is useful to obtain a readout of LiDAR data points in Cloud Compare, perhaps to determine the height value, or the intensity value of a LiDAR point. This post illustrates how to read out coordinate values in Cloud Compare.
  1. In Cloud Compare, load in a LAS file, e.g. Serpent Mound Model.las.

    The Global Shift/scale dialog box appears.



    Note: Real LiDAR data have large coordinate values requiring double data types, but most 3-D software like Cloud Compare works with coordinates in float data types internally. So in order to preserve the LiDAR coordinates in Cloud Compare, it may be necessary to apply some coordinate offset and/or scaling so that the LiDAR data points can fit into float data types. So when you load a LAS file in Cloud Compare, it will calculate and recommend an offset/scaling values before importing, as shown in the screen shot below.
  2. Click Yes.

    The LAS file is loaded; its data points are globally shifted and scaled.
  3. In the toolbar, click the Point picking icon.



    A point picking toolbar appears on the top right corner.
  4. By default, the first command (Select one point and displays its info) on the left is active. If not, click on it.
  5. Click on one LAS point.

    A balloon appears showing the X, Y, Z and a scalar value.

    Note: the xl, yl, zl on the left are local float data type coordinates. The xg, yg, zg on the right are the actual LiDAR data point vertices. The Point Source ID is the current scalar value.
If you want to get the read out to show another scalar field, you have to set the desired field before entering the Point Pick command, as described below.
  1. In the Tree pane, select the point cloud node, e.g. Serpent Mound Model.

    The Properties appear below the Tree pane.
  2. In the Scalar Fields | Active field, choose the desired field, e.g. Intensity.

    The point colors change to intensity values.
  3. Now, use the Point Pick command to readout a point.

    The readout balloon now shows the selected scalar field - Intensity.

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