Working with Point Clouds

February 21st, 2014

A point cloud is basically a large collection of points that are placed on a three-dimensional coordinate system.  Point cloud files greatly speed the design process by providing real-world context where you can re-create the referenced objects or insert additional models.  Point clouds are derived from raw data gathered by using a 3D scanner to obtain points from such things as buildings, topographies, or manufactured items. 

Before you can use the data in your drawing, however, it needs to be converted to a point cloud file.  This process is sometimes referred to as indexing.  You can use AutoCAD® Architecture to convert raw scan files to an ISD or PCG format.  You can use Autodesk’s ReCap™ product to convert raw scan data to an RCS format.  Autodesk ReCap can also save files in an RCP format that serves as a project file that references multiple RCS files.  Both formats can be attached to an AutoCAD Architecture drawing.

Creating Point Clouds from Scan Files

A scanned data file can be converted to a point cloud file that can then be attached to your drawing.  To do this, begin by clicking the Insert tab of the ribbon, Point Cloud panel, and then select Create Point Cloud.  In the Select Scan File dialog box, find and select one or more files that you want to use to create point clouds.  You can choose the following formats: LAS, XYB, FLS, FWS, XYZ, TXT, ASC, PTG, PTS, PTX, CLR, and CL3.  In the Create Point Cloud File dialog box, enter the settings for the imported point cloud, including whether to merge the files, where to store the point cloud files, and what point cloud file format to use (see Figure 1).  If you import more than one file, you can merge them by selecting Merge All Scan Files into a Single Point Cloud.  When selecting what point cloud format to use, you can select the Autodesk format (PCG) or Ambercore (ISD).  With PCG files, you can import such properties as color, intensity, and normal and custom attributes. 

Now, click the Create button to start the process, which can take minutes or hours, depending on the file size.  The dialog box is minimized, so you can continue to work while the scan is in progress.  When the process is complete, the Status column in the table changes to "Click to Attach."

To attach the new point cloud file to the current drawing, you can either click the Click to Attach message or click the link in the balloon message on the task bar.  While point cloud creation is in process, hover the pointing device over the point cloud icon in the drawing status bar in order to view the status of the background point cloud creation.  To cancel a point cloud creation process, while the raw point cloud scan files are being indexed, you can either right-click point cloud icon in the drawing status bar and select Cancel Point Cloud Creation, or you can click cancel in the Create Point Cloud File dialog box.

Figure 1: Create point cloud

Attaching Point Clouds

To attach a point cloud file as an external reference, begin by clicking the Insert tab of the ribbon, Point Cloud panel and then select Attach.  In the Select Point Cloud File dialog box, find and select an ISD, PCG, RCS, or RCP file to attach to the drawing and click Open.  In the Attach Point Cloud dialog box, specify your preferences for insertion point, scale, and rotation (see Figure 2). 

If you would like to prevent the attached point cloud from being moved or rotated, select Lock Point Cloud.  You can control the individual scan file settings in the attached RCP file.  You should turn on this setting if you do not want your drawing to be affected by changes to the on/off status of individual scan files that are referenced in the reality capture project (RCP) file.  To do this, at the Command prompt, enter POINTCLOUDVISRETAIN.  Then enter either 0 or 1.  For zero (0), the drawing inherits the most recent on or off status of individual scan files referenced by the attached RCP file.  For one (1), the drawing retains the on or off status of individual scan files at the time the RCP file was attached.

Figure 2: Attach point cloud

Working with Point Clouds

Once a point cloud is attached to a drawing, you can modify it, use it as a guideline for drawing, change its display, or apply a color mapping to distinguish different features.  You can modify an unlocked point cloud in several of ways.

  • Filter un-needed points by clipping – You can create one or more clipping boxes to show only the most relevant areas of the point cloud.  Drag the clipping boundaries to change the display and turn off or invert the clipping filters as you work.
  • Modify point cloud density – You can manage program performance and visual noise by increasing or decreasing the number of visible points.
  • Standard editing operations – You can cut, copy, paste, move, scale, rotate, stretch, and erase a point cloud.
  • Edit properties – You can change general properties such as color and layer in the Properties window. You can also modify the insertion point, rotation, and scale as well as turn locking and clipping on or off and control whether the color is derived from the source or the current color settings.
  • Use components as a reference when drawing – You can turn on the Node object snap and snap to individual points as you draw.  You can also snap to the insertion point.
  • Use color stylization – You can use color stylization to help you analyze features within the point cloud.  You can retain the original scan colors or specify color stylizations that are based on objects, point orientations, or intensity.

For point cloud files that inherit intensity values, intensity stylization helps distinguish between features such as foliage and buildings.  Use different color schemes such as Spectrum for more complex images or Grayscale for simpler visualization.  You can use color mapping on both locked and unlocked point clouds.  You can print a point cloud and retain the color stylizations in all visual styles except for 2D wireframe and wireframe.  It is important to note that the MIRROR3D command copies and moves a point cloud, but does not mirror it.  You cannot explode a point cloud.

Changing Point Cloud Density

You can control the number of displayed points to help you manage program performance and decrease visual noise.  You can change the maximum number of points in the drawing, which is controlled by the POINTCLOUDPOINTMAX system variable only for 64-bit operating systems.  Increasing the limit improves visual fidelity for the point clouds, whereas lowering the limit improves system performance.  This option is disabled on 32-bit systems, which are limited to 1.5 million points.  Begin by clicking the Application menu and select Options.  In the Options dialog box, 3D Modeling tab, drag the Maximum Point Cloud Points per Drawing slider to change the number of points that can be displayed in the drawing.

You can change the density of all displayed point clouds.  To do this, begin by clicking the Insert tab of the ribbon, Point Cloud panel, and select Density slider (see Figure 3).  You can now either drag the Density slider to increase or decrease the percentage of cloud points that are displayed in the drawing or you can enter a value that represents a percentage of the maximum number of points set by POINTCLOUDPOINTMAX.

You can change the density of displayed point clouds during Pan, Zoom, or 3D Orbit.  Lowering the real-time density degrades the point cloud display during panning, zooming and orbiting, but makes those operations quicker.  To do this, begin by clicking the Insert tab of the ribbon, Point Cloud panel, and then select Realtime Density slider (see Figure 3).  You can now either drag the slider to increase or decrease the percentage of cloud points that are displayed during real-time pan, zoom, and 3D orbit, or you can enter a value that represents a percentage of the maximum number of points that can be displayed in the drawing during pan, zoom, or 3D orbit.  This value represents a percentage of the maximum number of points set by POINTCLOUDPOINTMAX.

Figure 3: Adjust point cloud density

Point Cloud Clipping

If needed, you can clip or hide a portion of a selected point cloud.  If you wish to create a 2D rectangular or polygonal point cloud clipping boundary, then in the drawing area, select the point cloud.  Now, on the Point Cloud tab, Clipping panel, select Create Clip Box flyout.  Now, you can either Select Rectangular or Select Polygonal on the flyout (see Figure 4).  If you Select Rectangular, on the XY plane of the drawing area, specify diagonal corners of the rectangular clipping boundary and press Enter.  If you Select Polygonal, on the XY plane of the drawing area, specify three or more segments for a closed polygonal boundary and press Enter.  The point cloud points that fall outside the defined clipping boundaries are hidden.

Both rectangular and polygonal clipping boundaries can be reshaped.  In the drawing area, select a point cloud.  Select a grip on the clipping box and when it turns red, drag it to change the clipping box shape.  The point cloud display is updated after the drag operation is complete.

If you wish to convert a polyline to a 2D clipping boundary, in the drawing area select the point cloud.  On the point cloud tab, clipping panel, Create Clip box flyout, and then select Polyline (see Figure 4).  In the drawing area, select a polyline to define the clipping boundary.  The polyline can be open but must have straight segments.  The point cloud points that fall outside the defined boundaries are hidden.  Sometimes, however, you may find it useful to have a polyline that coincides with a 2D point cloud clipping boundary.  To create the polyline, enter POINTCLOUDCLIP at the command prompt.  Then Enter p (generate Polyline).  Now, in the drawing area select a point cloud.  The new polyline will inherit the current layer, linetype, and color settings.

A 3D point cloud clip box can be reshaped based on the bounding box.  To do this, select a point cloud and then click the Point Cloud tab on the ribbon, Clipping panel, and then select Clip Box.  A clipping box that is the same size and shape of the point cloud bounding box is displayed.  If the point cloud already has a clipping box that has been modified, you can choose whether to restore the default clipping box or retain the modifications.  To adjust the clipping box, drag the grips using either Standard grip (square) or Height grip (triangle).  Standard grip resizes the length and width of the clipping box along the XY plane of the point cloud object.  Height grip resizes the height of the clipping box along the Z axis of the point cloud object.

The point cloud clipped view can be turned on and off within a drawing.  When the ribbon button is highlighted, select a point cloud clipping boundary or clipping box.  Click the Point Cloud tab on the ribbon, Clipping panel, and then select Show/Hide.  This turns the view on or off.  Sometimes instead of turning it on or off, you may need to remove it completely.  Select a point cloud and click the Point Cloud tab on the ribbon, Clipping panel, and then select Delete Boundary.  Select the clipping boundary or clipping box that you want to remove and press Enter.

Figure 4: Point cloud clipping boundary

Color Maps that Display Point Cloud Intensity

Some types of scan files contain color intensity data that can be retained in the point cloud.  These file types include LAS, PTG, PTS, PTX, CLR, and CL3.  To assign colors to map the point cloud intensity, in the drawing area select a point cloud that contains intensity data.  Click the Point Cloud tab on the ribbon, Visualization panel, then select Intensity Color Mapping.  In the Point Cloud Intensity Color Mapping dialog box, adjust the following settings.

Color scheme – Select a color scheme to help illustrate the point cloud intensity mapping.  Colors range from Spectrum to grayscale and single colors.

Color ramp – Drag the sliders to define the color range to use in the mapping.

Intensity minimum and maximum – Enter values between 0.000 and 1.000 to specify the percentage of intensity values to be displayed using the color map stylization. These values represent the high and low values of the entire range of intensity values associated with the selected point cloud.  Points with intensity values that are outside the limits you specify are displayed using the original scan colors.

Once that’s complete, click Apply to test how the settings affect the selected point cloud.

If you are not a fan of the color scheme, you can change it in the Properties palette.  If the Properties window is not displayed, select any object and then right-click the object and select Properties.  In the drawing area, select the point cloud.  In the Properties window, under Point Cloud Visualization, Intensity Color Scheme box, select a different option.  You can also perform this function using the ribbon, which I find a little easier.  In the drawing area, select the point cloud.  Then click the Point Cloud tab on the ribbon, Analysis, then select Intensity.  Now you can select a color scheme under the Spectrum flyout or select Intensity Color Mapping and select the color scheme you want to use (see Figure 5).

Figure 5: Point cloud intensity color mapping

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About the Authors

Melinda Heavrin

Melinda Heavrin

Melinda Heavrin is a CAD Coordinator & Facility Planner for Norton Healthcare in Louisville, Kentucky.  She has been using AutoCAD Architecture since release 2000.  Melinda can be reached for comments and questions at melinda.heavrin@nortonhealthcare.org.

 

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