Point Cloud - Polygon Mesh. Wannes Van Isacker - Industrial Design 15

Transcription

1 Point Cloud - Polygon Mesh Wannes Van Isacker - Industrial Design 15

2 3D-SCANNING About 3D Scanning To get started with 3D scanning you first have to understand a little how the scanner works. The scanner projects a specific raster image on a surface, then takes pictures of the surface how the raster is deformed by the difference in depth of field. When moving around the object you want to scan you must always have overlapping information with the previous picture, think of it like taking a panoramic picture. Tips and tricks Knowing this, you probably understand that use of an optical technology has its limits. Reflection and focal distance are the most important aspects to keep in mind. When scanning a reflective object you might want to apply a nonreflective coating, washable spraypaint is the way to go! The focal distance is suggested by 2 laser points which converge at the right distance. always try to keep the same height as in the previous scanned image, this way the software is able to track your movement and stitch images together for you. All further specific scanning details about the usage of the scanner and software are provided in the Noomeo Scanner manual. 1

3 SOFTWARE Numisoft scanning software In the illustration on the left hand side is the result of a completely merged 3D point cloud, the bottom of the bottle (at the top in the picture) was scanned separately from the contour of the bottle. Because this resulted in a separately scanned image we had to manually stitch both 3D files together This process results in a point-cloud file, containing no more than xyz-coordinates and optional RGB information of every scanned point, the image below shows an example of a pointcloud file opened in notepad. Geomagic meshing software To convert a point cloud in a geometric shape, all dots must be connected with small surfaces, these small surfaces are called polygons. In the image on the right you are able to see converted point-cloud into a polygon geometric shape, the Geomagic software even maps rgb information to the polygon model. Making it possible to see the label of the ketchup bottle. Sometimes the software doesn t completely generate a correct polygon model, which results in holes of the model and sometimes even overlapping surfaces. Anomalies need to be corrected manually in post-processing software. At the end of this polygonizing process you are able to save your model as an STL file and you re ready to start post processing the polygon model in a CAD environment. 2

4 About GOM Inspect GOM Inspect is freeware (free software) made to inspect pointclouds and polygon models. It also has possibilities to edit meshes and convert point-clouds into polygon models. Learning new software is always a process of trial and error therefore we d like to provide you a short manual to create a polygon model of a point-cloud provided by the Numisoft software. You can download the software on the website of GOM. Please note that no commercial use is allowed by GOM. Getting started Once started the software it gives a short overview of its possibilities, choose sample project to open the software. On the first time running the software it requires to check your graphical adaptor settings and sort of benchmarking your hardware. When the software is completely loaded, a sample project appears on the screen, we won t need this file so just create a new project. Pointcloud to Mesh Import the point-cloud created with the Numisoft scan-software. The extension of the file you are looking for is.asc this file contains all coordinates of the point-cloud. When the file is selected the GOM software wants to know which formatting is used. Therefore you must match all xyz coordinates to the right column. When imported the pointcloud you are able to see the dots in a 3D environment by selecting the icon Mesh Editing. Once the pointcloud is visible you can start making a polygon model by selecting Polygonize Point Cloud. Download GOM Inspect Software Installing GOM Inspect When downloading the container file, you have to unpack the file to a steady hard drive location where the software can stay for a while. No installation is needed, just run the software. Easy user accessibility can be provided by creating a shortcut to the desktop. The predefined option to match the right format is Pointcloud (scanner). When this option is selected the rest of the import process is done automaticaly by the software. 3

5 If all goes according to plan, when hitting OK the automatic mesh is created. Visibilty workflow When the mesh is created the pointcloud is still visible. This will be a hindrance during post processing. Therefore we advise you to make the pointcloud invisible for the following processes by unchecking the visibility mark. To select objects in the GOM software right click RMB in the workarea, then select Through Surface. The easiest way to accurately select objects is by left clicking/draging LMB around the object. When the area is completely selected end the selection proces by right clicking RMB. After selecting the object to mesh you must choose the correct settings in order to adjust the accuracy of the mesh. The more accurate the mesh, the longer you have to wait until the meshing is complete, depending on your computer hardware and the number of points. When increasing Min. distance of used points, the number of polygons decreases. We would recommend changing this value from 0 to something higher if the meshing takes longer than 10 minutes because your system might run out of memory and crash. 4

6 Result Meshing Due to the polygonizing process the object is displayed as a combination of many surfaces. As in the Geomagic software post processing is needed. A lot of small irregularities which deform the smooth surface need to be corrected. Undoubtedly there are a few holes in the model which need to be closed. From here on it is possible to just export the mesh as an.stl file and do all post processing in other CAD software which has reverse engineering tools built in. Because most CAD systems don t integrate this ability as standard but more as an extension packet which will cost a lot of money. We suggest to do some post processing in the GOM software environment. Closing holes automatically There are several built-in options to close holes, first method is the Automatically close holes function. The technique speaks for itself, just select the whole geometry and tweak some of the parameters until you get it right. It is best not to set the Max. hole size to big because strange things will happen. The top of the model in the example will not be closed by this option because it is too big and needs a human touch. 5

7 Closing holes interactively When completing the automatic closing holes process the biggest gaps won t be filled. That s where the Interactively close holes tool comes in handy. With this tool you first have to select the geometry you want to heal and then you must suggest where the hole is located by drawing a line near the edge of the hole. In my experience the best results are made by drawing a line diagonally over the hole and closing it in two times. When you agree with the software s suggestion you just hit the fit hole and go to the next hole icon. Continue this process until there are no holes anymore, exit the tool by hitting ESC. 6

8 Smooth surface To make the surface more smooth use the built-in Smooth tool. This is a really ease to use function, just select the whole geometry and tweak the Filter radius in combination with the Surface tolerance. By increasing the filter radius and tolerance the surface gets more smooth but diverges more from the original shape. The preview area gives a good estimation of the end result. Before smooth After smooth 7

9 Result When 3D scanning I d suggest using the GOM software to clean up the polygon model instead of other CAD software because it is relatively fast and very basic in its functionality therefore it is very easy to use. Don t forget you are working with freeware and it s the first time you use the software, so easy-to-use is a relative understanding, it took me about a little more than hour to figure all this out by trail and error. Export mesh Finally you are able to export the geometric model as STL to continue further modelling in CAD invironment. Don t forget to select the geometry by clicking on it, otherwise you won t be able to click export. 8

10 Point Cloud - Polygon Mesh Wannes Van Isacker - Industrial Design 15