Geomagic系列教程點云處理

1、rQindr°pgeomQgicStudio TutorialPoint Cloud EditingObjective:Learn to edit a point cloud Use the various sampling functions to reduce the number of points while maintaining the geometric shape. Improve the dataset by reducing the noise caused by seannes. Use the Wrap operation to polygonize the

2、point cloud.Files:.Geomagic Studio 6Tutorial Datalatch-scan.wrpOpen latch-scan.wrp This is sean data of an automotive sheet metal part, containing about 900,000 points. To create a NURBS surface of this part, we must first create a polygon mesh through the points. However, before doing that, there a

3、re options available for reducing both the number of points and the inherent noise of the scan data.WM IkraJITo be able to rotate around the model more quickly and efficiently, go to the Display Panel on the left hand side of the screen and set the Dynamic Display value for points to 25%. This means

4、 only 25% of the data will be visible as we rotate, improving rendering speedsD is pl ay % (S talic ) Dynamic)Points 1100/ |Polps | 100 | 1003. First, we must clean up the stray points, known as outliers, that exist around the outside of the part. They are usually easy to identify as points that are

5、 far away from the main point cloud and do not represent any geometry that we want to keep Outliers typically occur when digitizers, such as laser sea nn ers, in advertently sea n objects in the background, such as tabletops, walls, support structure, etc.4. Select Top View from the Views toolbar.5.

6、 Zoom in on the line of points visible now on the left side of part, shown below.6. Use the Lasso Tool to select only these outliers, as show n below .If you inadvertently select points you do not want to delete, simply hold down Ctrl while dragging the Lasso Tool around them to deselect.7. Use the

7、Erase comma nd to delete the selected poi nts You can also use the Delete key on the keyboard. Select Ctrl+D to fit the model to the screen.總 8. In stead of manu ally deleti ng all these outliers, we can also let the software detect them automatically From the Edit->Select menu, choose Disconnect

8、ed Components. Change the Separation dropdown menu to Low, and leave the Size value at 5% This function selects clusters of points that are separated from the majority of the points. Separation indicates how far the clusters can be to the main cloud and still be selected, and the Size determines how

9、 large the clusters can be. Thus, we asked the software to select any cluster of points with 5% or less of the total number of points, with a relatively low separation from the main cloud.9. Click OK to exit the comma nd. Use the Erase command to delete the selected points. Notice how all of the str

10、ay points have been deleted.10. Before doing anything else, click Edit->Undo, or type Ctrl+Z. This will restore all of the outlier points. Many of the n ewest functions in Geomagic Studio in elude the ability to perform multiple operations with one function. The Reduce Noise function is one examp

11、le of that.11. Clear any selected points using Edit->Clear All, or type Ctrl+C. The following is a brief explanation of scan noise:Frequently, during the scanning or digitizing process, an element of “noise” is introduced into the data. “Noisy data" is identified by a rough, uneven appearanc

12、e in the surface model and is due to such factors as small vibrations in the scanning device, inaccurate scanner calibration, or poor preparation of the physical object's surface Geomagic has a function called Reduce Noise that helps to minimize the amount of noise present in the scan and, thus,

13、 better represent the true shape of the object. Below is a picture of a polygonal model of a typical part before and after the noise reduction process:Before.12. Select Reduce Noise from the Points menu. Choose the Free-form Shapes option (use the Prismatic Shapes option when you have sharp edges or

14、 small details to preserve). Set the Smoothness Level to Medium.13. Under Max Displacement, toggle on the Limit checkbox and set the Limit to 0.1 mm. This option allows the user to limit the movement of data points during the smoothing process The user can then choose to either select or delete any

15、points that would have moved more than the specified limit. For this example, choose the Select Outliers option. Also, toggle on the Include Isolation Points checkbox. This will automatically find and remove disconnected components, or outliers, which are very far from the point cloud (i.e. isolated

16、).14. Click Apply to begin the calculation. The error in the data, caused by the seanner, is averaged to produce a smoother surface The Average Distance and Standard Deviation values are reported under Statistics at the bottom of the dialog box.> Quick Tip: This function is best run on larger dat

17、a sets (i.e. before doing any sampling).15. Notice that some points are red, or selected These represent the outliers (points that are far away from the main point cloud, or points that would have had to move more than 0.1 mm during the smoothing process). It is safe to assume these may have been er

18、roneous points resulting from perhaps improper surface coating or an uncalibrated digitizer. In fact, you can even see in the image at left above that some of the points are linear. This was a bad “swipe” with the arm-mounted laser seannethat collected the points. Perhaps the mounti ng table had mov

19、ed betwee n sea ns. Regardless, the Reduce Noise function helps identify and correct these flaws.16. Change the toggle from Select Outliers to Delete Outliers. This will automatically delete all of those bad points.17. Near the bottom of the dialog, toggle on the Display Deviations checkbox. You wil

20、l see a spectrum appear on screen and the points will inherit a color based on their relative deviations to their original positions. This helps to visualize which points are moving and by how much. Toggling on the Edit Spectrum checkbox allows you to customize the spectrum band values18. Click OK t

21、o dismiss the Reduce Noise dialog Though difficult to see because there is no surface, the data has been smoothed slightly to correct some of the in accuracies of the sea nning system. At the same time, we detected and deleted some of the outlier points introduced during seanning which may have caus

22、ed a poor surface down stream .It should be noted that Reduce Noise is not always required .It depe nds on the sea nner being used and how much noise is present in the data19. Since this part is fairly simple, we can reduce the number of points while still maintaining an accurate representation of t

23、he part Select Uniform Sample from the Points menu.20.1 n this dialog, we can determine the spaci ng value three ways: by setting an absolute (or average) spaci ng, picking two points to set the spaci ng, or defi ning a target nu mber of points we want to end up with. For this example, we will choos

24、e the latter. Toggle on Define Spacing By Target and set the number of Points to 250,000.21. Under Optimize, the user has the option to set a Curvature Priority. Setting this to Max would mean the software would attempt to keep more points in areas of high curvature where more detail is needed, such

25、 as on radii or corners. Since this part has no real sharp corners, we will leave it set at the default, Min.22. Toggle on the Keep Boundary checkbox to retain points along model boundariesand hit Apply. This begins the sampling calculation. After a minute or so, you will have approximately 250,000

26、points, evenly distributed around the part surface Click OK to exit the comma nd.23. Select Wrap from the Points menu. Choose the Surface wrap option.> Quick Tip: The Volume Wrap option is useful for polygonizing sparse, non- uniform point clouds. However, the computation time and memory usage ar

27、e greater. It is recommended that the user try polygonizing with the faster, memory-efficient Surface Wrap option first. If result is undesirable, try again with Volume Wrap.24. Toggle on the Advanced Options checkbox. Here, as in previous dialogs, you can perform multiple operations at one time, in

28、cluding Uniform Sampling and Noise Reduction. Since we have performed these two operations already, we will not do them again here. Set Noise Reduction to None and toggle off the Point Spacing checkbox.25. Toggle on the Target Triangles checkbox. This activates a unique new slider that is very useful. It allows a user to choose whether Performanee (speed, low memory usage) or Quality (better polygonized result) is m