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.

Monday, March 13, 2017

Batch sample or convert videos to animated GIF files WebApp

I wrote a WebApp VidzGif for batch sampling or converting video files into animated GIF images that works with just a Web browser without uploading the videos to a server for processing.

To use this WebApp, do the following:

  1. Open up the WebApp at https://dominoc925-pages.appspot.com/webapp/vidzgif/default.html with a Web browser.


  2. Optional. Click Settings. Set the desired parameters, e.g. sample interval, duration, etc.
  3. Click the Browse button and select one or more video files. Or drag and drop one or more video files into the dashed box.



    The videos are sampled and rendered into GIFs.
  4. To save out the GIF, right click on the image and choose Save image as.

Monday, March 6, 2017

Interactive cross-section in Cloud Compare

After loading LiDAR point clouds in Cloud Compare, it helps sometimes to cut a cross section or profile to get a feel for the land. There is a couple of Segment commands but the one I use for this purpose is the Cross Section Tool with the graphic interactors.

The following steps show how to use the Cross Section Tool.
  1. Load a point cloud file, e.g. Serpent Mound Model LAS Data.las, into Cloud Compare.
  2. Select the cloud in the DB Tree pane.


  3. Select Tools | Segmentation | Cross Section.



    The graphic interactors (the large 3D arrows pointing to the X, Y, Z axes) and Cross Section box appear
  4. Drag a cone of an interactor to thin the cross section box.

  5. Drag the torus of an interactor to rotate the cross section box.

  6. Adjust the interactors and camera view until the desired orientation is achieved.

    Note: if you wish to segment out the cross section into another cloud, click the Tick icon on the Cross Section tool box. Otherwise, click the X icon to exit the command when done.
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