Scan, Cleanup, and Remodel
Contents
1. each is better suited to different situations needs and requirements If the job is to duplicate and original as accurately as possible capturing unique details and differences in the object as closely as possible then scanning and leaving the data as a mesh is about as good as it can get Sharp edges and creases in the Original will be rounded a little The little flaws in your sample note the rippling effect in the cap from the threads will be captured and even the thickness of the paper label can be seen A small amount of surface noise or orange peel roughness is to be expected and can be seen in the apparent roughness of the scan This can be reduced with the Rhino Smooth command If the job is to try to reverse engineer an object from an original example but also clean up the data in an attempt to capture the original design then the extra work of modeling the part using NURBS surfaces may be worth the effort Even at that the results will not be a perfect replacement of the original because of the assumptions the Rhino operator made in the reverse engineering process Copyright 2006 Robert McNeel amp Associates 182. the same way Harvest curves from the mesh Use the surfaces as visual reference and the symmetry of the shape to draw curves that capture the primary shape The Section or Contour commands can also slice through the mesh to make curves These curves would accurately follow the mesh facets but they would be unsuitable for making good NURBS surfaces without extensive clean up and simplification Copyright 2006 Robert McNeel amp Associates 12 SCAN CLEANUP AND REMODEL New curves ready for surface creation Create surfaces Use NetworkSrf to make the replacement surface Make a surface for the base using the scanned surfaces as reference Add the bottom relief details later Copyright 2006 Robert McNeel amp Associates 13 SCAN CLEANUP AND REMODEL To model the slightly domed top draw curves that follow the centerlines in opposite directions crossing over the middle Then copy the curves to the ends of the other centerline curve to make a network of curves that follows the curved shape of the top Use NetworkSrf to make the surface Trim the three new surfaces with each other to make the basic replacement body Here is before Copyright 2006 Robert McNeel amp Associates 14 SCAN CLEANUP AND REMODEL And after After trimming use ShrinkTrimmedSrf to minimize the extra control within the trimmed surfaces and Join the surfaces into a solid Use the same techniques
3. 68 8EC6 42ed A962 26DEB8CC8F9A e Plug in Rhino Render e description Rhino Renderable Object UserData e saved in file no e copy count 2 Geometry e Valid mesh e Open polygon mesh 229147 vertices 445784 polygons with normals e bounding box 0 946531 1 08 0 0272168 to 1 00295 0 980724 4 7215 Copyright 2006 Robert McNeel amp Associates 4 Pa 4 yy SCAN CLEANUP AND REMODEL Fix mesh errors These errors indicate the following commands should be run ExtractNonManifoldMeshEdges Delete them after extraction Non manifold edges are surface or mesh facets edges that are joined to two or more other edges at the same time Rhino does not allow nonmanifold edges in surface models ExtractDuplicateMeshFaces Delete them after extraction Next run the MatchMeshEdge command with a setting of 0 001 This command moves face edges of an open mesh to meet adjacent face edges exactly so the mesh will be closed and can take some time to run depending on the number of open mesh facets This process may take about 10 minutes Here is the result Most of the seams are joined up but not all After this run CheckMesh again It may find additional non manifold edges and duplicate faces created by MatchMeshEdge If it does run ExtractNonManifoldMeshEdges and ExtractDuplicateMeshFaces again and delete the extra faces Next run the FillMeshHoles command When automatically filling holes it can it create more nonmanifold edges Run
4. ExtractNonManifoldMeshEdges again and delete any extracted faces Close the mesh All of the relatively automatic clean up work has been done but we still are not quite finished At this point the model should have an open not water tight good mesh with a few complicated holes that still need to be fixed The rest of the clean up work is more manual and will require a few additional mesh editing tools To effectively use these tools we will be using some new display tools In the image below we ve changed to a wire frame display with naked edges set to magenta to simplify selection and zoomed in on a hole and intend to fix the hole However the small mesh facets on the far side of the mesh are complicating the display and will affect picking Copyright 2006 Robert McNeel amp Associates 5 A 4 yy SCAN CLEANUP AND REMODEL Use the ClippingPlane command to mask the mesh facets in back Since these holes are on the front of the bottle use the ClippingPlane command in the Front viewport By default the clipping plane is oriented to mask the objects in front In this case we want to mask the objects in back so we will Rotate the clipping plane 180 degrees Here is a view of the Perspective viewport showing the Front viewport clipping plane Here is the result of it in the Front Viewport Copyright 2006 Robert McNeel amp Associates 6 SCAN CLEANUP AND REMODEL Here is a shot of the Front viewpo
5. Using Rhinoceros scan Cleanup and Remodel ee wy SCAN CLEANUP AND REMODEL Copyright 2006 Robert McNeel amp Associates All rights reserved Rhinoceros is a registered trademark and Rhino is a trademark of Robert McNeel amp Associates Copyright 2006 Robert McNeel amp Associates ee Y SCAN CLEANUP AND REMODEL 1 Introduction This document shows how to do two things e Bring the meshes into Rhino and clean them up making them suitable for rapid prototype STL printing as a single closed mesh A scan from the NextEngine Desktop Scanner is used as the example More information on the NextEngine scanner can be found at www nextengine com e Use the cleaned up mesh as a basis for making a smooth accurate NURBS model suitable for any down stream manufacturing process Reverse Engineering A Short Discussion There is a lot of confusion about scanning Part of this confusion is from the misinformation passing between well intentioned users and part is from the overly general nature of the questions asked For our purposes we will define reverse engineering as taking an existing object and using some process to make more The two primary reasons for doing this are to make duplicates for reproduction and to make replacement parts When making physical duplicate the goal is to model as accurately as possible preserving the odd nature and special features of the object This might be done for historical pre
6. count 179 Geometry Copyright 2006 Robert McNeel amp Associates 9 SCAN CLEANUP Valid mesh Now the mesh is closed mesh and ready for rapid prototype printing Copyright 2006 Robert McNeel amp Associates AND REMODEL 10 A S SCAN CLEANUP AND REMODEL 2 Reverse Engineer an Accurate NURBS Model Start with the cleaned up closed mesh Technically starting with mesh clean up first is not necessary but it will make harvesting complete curves a little easier Begin by using a series of commands for breaking up the mesh into logical pieces from the stand point of Rhino surface modeling Put the different pieces on different layers to make them easier to manage Experimenting showed that ExtractConnectedMeshFaces with a setting of less than 15 degrees worked to split the bottom of the bottle from the cap This took advantage of the greater angle of the mesh facets in the groove between the body and cap The next step was to split out the leaf detail on the cap Sketch an outline curve in the top viewport and use point editing techniques to adjust the curves Then project the curve onto the mesh and use MeshSpillit Copyright 2006 Robert McNeel amp Associates 11 SCAN CLEANUP AND REMODEL Use a similar procedure to trim the cutaway on the bottle base except used the apparent intersection to split the mesh instead of projecting the curve to the mesh Split off the top of the cap
7. display configuration called Shaded Mesh Editing with the following settings Display Mode Options Change these settings to create the two new named display configurations All other controls should be left at default values Section Viewport settings Shading settings Visibility Objects Meshes Mesh Edge Settings Control Background Shade objects Flat shading Backface Settings Color Show isocurves Show mesh wires Naked edge color usage Naked edge color Naked edge thickness Color reduction Name Shaded Mesh Editing Use Application Settings On On Single color for all backfaces Cyan Off Off Use single color for all naked edges Magenta 2 20 Name Wireframe Mesh Editing Use Application Settings Off N A Use front face settings N A On On Use single color for all naked edges Magenta 2 20 Flat shading disables the automatic display smoothing of meshes Backface Mesh facets and surfaces have front and back directions Backfaces are oriented to be facing the interior of a closed volume Naked edges are mesh or surfaces edges that are not joined to other mesh or Surfaces edges Copyright 2006 Robert McNeel amp Associates Pa 4 yy SCAN CLEANUP AND REMODEL Opening the scan NextEngine is ScanStudio application can export their aligned trimmed and blended meshes in a variety of formats Rhino can
8. lling the hole Use the same techniques using view clipping planes deleting misplaced mesh facets and filling holes to work your way around the mesh and fix all of the holes and naked edges Some other commands useful for doing this clean up work are PatchSingleFace Fills a mesh hole with a single mesh face SplitMeshEdge Divides a mesh edge to create two or more triangles SwapMeshEdge Transposes the corners of mesh triangles that share an edge When all of the holes are filled and the naked edges dealt with the mesh will be closed The Details button on the Properties dialog box will report e Geometry Valid mesh Closed polygon mesh Additionally run CheckMesh one more time as a second check This is a good mesh General information about this mesh e Mesh does not have any degenerate faces e Mesh does not have any zero length edges e Mesh does not have any non manifold edges e Mesh does not have any naked edges e Mesh does not have any duplicate faces e Mesh does not have any faces that could make it better if their directions were flipped e Mesh does not have any disjoint pieces e Mesh does not have any unused vertices ID d7fd1a57 4be1 4636 8232 Obd 7ffc58fa7 467784 Layer name Default Render Material e source from obj e index 18 Attribute UserData e UserData ID BOEE2168 8EC6 42ed A962 26DEB8CC8F9A Plug in Rhino Render description Rhino Renderable Object UserData saved in file no copy
9. ng Use the ShowEdges command to help find them or set the display mode to paint them a different color Try the FillMeshHole FillMeshHoles or MatchMeshEdge commands to remove naked edges Copyright 2006 Robert McNeel amp Associates 3 ee MY SCAN CLEANUP AND REMODEL e Duplicate faces Fix with the ExtractDuplicateMeshFaces command e Faces with reversed normals Fix with the UnifyMeshNormals command e Disjoint pieces Fix with the SplitDisjointMesh command e Unused vertices Unused vertices do not usually cause a problem and there are no commands to for removing them in Rhino Specific details on these commands can be found in the Rhino Help file CheckMesh reported This is a bad mesh Here is what is wrong with this mesh e Mesh has 11 non manifold edges e Mesh has 6 duplicate faces e Skipping face direction check because of positive non manifold edge count Important things to consider with this mesh e Mesh has 14044 naked edges Although this does not necessarily mean that the mesh is bad e Naked edges can cause problems if the ultimate goal is STL output General information about this mesh e Mesh does not have any degenerate faces e Mesh does not have any zero length edges e Mesh has 88 disjoint pieces e Mesh does not have any unused vertices ID 8ba20560 dae9 483a a801 ea150a8662b5 49 Layer name Default Render Material e source from obj e index 20 Attribute UserData e UserData ID BOEE21
10. of sketching curves to make a surface for the bottle cutaway Here is the new surface and the scanned mesh for comparison Copyright 2006 Robert McNeel amp Associates 15 SCAN CLEANUP AND REMODEL The new surface fits well but shows a little undulation near the base One way minimize this flutter is with a little control point nudging This looks better Trim and join the surfaces Trim the surfaces with each other and Join them back together Here is what the model looks like it mi Copyright 2006 Robert McNeel amp Associates 16 SCAN CLEANUP AND REMODEL There are still a few details to finish splitting the cap from the bottle body blending out the edges adding the leaf detail to the cap and the rim relief detail to the base These modeling techniques are commonly used in Rhino surface modeling and not specific to reverse engineering from scanned data so they are not detailed here Here is the finished NURBS surface model Here is an STL mesh on the left generated from the closed solid polysurface side by side with the cleaned up scan from the original bottle on the right Flat shade is turned on so the individual mesh facets in both models can be seen Copyright 2006 Robert McNeel amp Associates 17 ee wy SCAN CLEANUP AND REMODEL Final results and summary Do not get the impression that one model is any better than the other They are different and
11. open all of them The preferred file format is OBJ 1 Start a new modeling session in Rhino using the Small objects Inches template Use File gt Import and select the Bottle OBJ file exported from ScanStudio It will come in as 17 different meshes grouped together Use Rhino transform commands to move and position the grouped meshes into a logical location for editing over the 0 0 origin See the Rhino training material from information on using these transform commands Right click the Perspective viewport title and change the display to Shaded Mesh Editing Imported meshes showing naked edges in Rhino Check the mesh The individual meshes in the OBJ file were grouped together keep them together Ungroup them and Join the 17 meshes into a single mesh to make them simpler to work with The first order of business is to clear up any easily avoided problems Rhino has several commands that are useful for checking and repairing mesh files start with CheckMesh Checks mesh objects for errors and reports problems which include Degenerate faces Fix with the CullDegenerateMeshFaces command Zero length edges Zero length edges typically are the result of degenerate faces Fix with the CullDegenerateMeshFaces command Non manifold edges Use the CullDegenerateMeshFaces command and then fix with the ExtractNonManifoldMeshEdges command Naked edges Naked edges are allowed but cause problems with rapid prototypi
12. rt showing the results of using the ClippingPlane Now in the front viewport zoom in on an area with naked magenta edges The mesh on the other side of the clipping plane will now not be displayed Front In the above image notice how some of the naked edges cross over each other These are mesh triangles that are complicating the closing of the holes and the reason the more automatic commands could not fix the holes for us Use the DeleteMeshFaces command to remove the facets that are crossing over other mesh facets Here is the same view with the overlapping mesh facets deleted See how the hole border is now clearly shown Front Use FillMeshHole singular to close the hole Copyright 2006 Robert McNeel amp Associates 7 AA y SCAN CLEANUP AND REMODEL Here is the result Front Sometimes it is difficult in the faster Wireframe Mesh Editing display to see what is really going on over these complicated holes When that happens switch over to the Shaded Mesh Editing display mode Then the problems will be easier to see Here is an example of another hole with mesh facets crossing over it Here is the same hole after deleting most of what appeared to be overlapping mesh faces Copyright 2006 Robert McNeel amp Associates 8 ee wy SCAN CLEANUP AND REMODEL Well defined holes like this one are ready for filling The two naked edges on the right indicate some facets should be deleted before fi
13. servation or restoration to mass produce a unique object like a special wood carving or to model a damaged knee joint for a prosthetic replacement for example The key is preserving the detail and accuracy from the original example When creating a new model working from a typical example of something that is worn or damaged and needs to be replaced the person doing the work needs to have a good understanding of the original part and the circumstances of its use In this situation the model will not precisely follow the original in order to compensate for the wear and damage to the original The key is to make an accurate model of what the original might have looked like before it was worn or damaged In both of these cases it is not possible nor realistic to think that reverse engineered part will produce an identical replacement Close inspection and comparison will always find small differences because of the processes used and decisions made by the skilled operator There are two primary ways to duplicate a part One is to use a process to make a mold of the original and make castings using the mold This process is outside the scope of this discussion The second is to take physical measurements or through a CMM or scanning process and make an electronic model that in turn can be machined or printed through one of the many rapid prototyping technologies Generally speaking if the part is mechanical in nature and direct measuremen
14. ts can be made from the part it is much faster to measure the part and model it using modern Computer Aided Design software like Rhino If the part it twisty or curvy it can be very difficult and time consuming to take direct measurements Just ask someone that measures clay models of concept or production automobiles and creates models from the data This is one example where scanning can save a great deal of time and capture a great deal of accuracy When laser scanning technology is used best results are obtained from objects with a light colored non reflective matte finish Dark reflective or fuzzy objects do not lend themselves to laser scanning Additionally scanning tends to melt detail Sharp edges and creases are rounded over and filled in a little when the mesh facets are fit to the scanned point data Copyright 2006 Robert McNeel amp Associates 1 ee XY SCAN CLEANUP AND REMODEL 2 Clean up for rapid prototype printing The NextEngine ScanStudio software can export to STL VRML OBJ and XYZ point file formats Rhino can read all of them OBJ is the preferred file format Set up Rhino display modes The five default named display settings do not lend themselves to editing dense meshes To work with dense meshes two new display configurations are needed Rhino V4 offers this capability to create name and save them Tools gt Options gt Appearance gt Advanced Settings allows this Create the first new named
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