Preparing Site Models for Milling

This document lists a set of steps for preparing a site model containing a terrain surface and extruded objects for milling on the GSD's Computer Numericly COntrolled (CNC) Router. This page is supplemental to the page Workflow for Automated Milling of Sites. We assume you have a sketchup model containing a terrain mesh, and tthe flat tops of the extruded objects, at the correct elevation above the terrain.

Import Model to Rhino, Scale and Shift to fit in Milling Material

Our terrain model starts out quite large, probably more than 100 feet in extent, but we need to scale it so that it fits on a relatively small piece of foam.We use Rhino as a tool for transforming the model -- scaling and shifting and rotating it into a coordinate space that the milling machine will be comfortable with.

Create new Rhino file: Large Objects / Inches
Import sketchup file.
Select all, and use Edit->Group to group everything
Choose Transform>Scale3d or Type Scale into the command window - choose origin of rhino model (in middle of grid).
With Snaps on, choose Surface->Plane->Corner to Corner to create a rectangular mesh 12" x 12" with one corner at the origin of your model.
Use the Arrow tool to Shift the the model into the box.
Use Transform>Rotate to rotate model to fit in the box.
Scale and shift and rotate again as needed to fit into the box with at least a half inch margin around the work.
If zooming/panning gets very tired, use View>Viewport Properties to set camera and target to be near the origin.
In one of your elevation viewports, move the model up so that the top of the model is just below 2 inches. Hopefully you still have an inch of material below, so that the foam won't warp or tear loose during the milling job.
Ungroup

Adjust Precision of the Rhino Model

Many of the representations in rhino are curves that are parmetrically defined, as opposed to lines which have explicit begining and end points, and whose intersections can be calculated fairly easily. Being curve-oriented is an advantage for some things, but it is a bit less exact. One thing that comes up when bringing in a very large site model and then scaling it down to an 8 insh square is that Rhino adopts a faily low precision when it opens the large model. Think of precision as the snapping tolerance used by the automated operations of the program itself. But when we get the model down to something small, we should adjust the precision accordingly, or else there will be problems -- particularly in the step where we have to connect up several surfaces to create a closed solid.

Go to Tools>Options>Units and set your Tolerances as follows:
- Absolute: 0.0001
- Relative: 0.001
- Angle: 0.001

Convert the Rooftop Polygon Surfaces to NURBS and Drape Terrain INtersection Curves

Rhino and Mastercam are surface oriented, and many of their operations are most happy when surfaces are expressed as continuos curve funcetions known as Non-Uniform B-Splines or NURBS. IN the next sequense of steps we will use the layer manager subsystem of rhino to put our buiklding tops on a new layer, and we will use a transformation tool to convert the polygons that are our rooftops to NURBs, and finally we will create outlines of these surfaces and project them onto the terrain surface. These lines will represent the place where the building meets the grouns and will be used to tell the router exactly how to cut around the buildings.

Select the Building tops. These have probably been grouped so that they will all select at the same time.
Use Edit>Layers>Edit Layers to open the Layer Manager. right click to reate a new layer for your tops.
While we are in the layer manager, create a new layer for the Building_contours and another for your Terrain.
Right click the Tops layer and use Change Object Layer to place all the building tops (selected) into this layer, and click the lightbulb to hide these tops for now.
Type meshtoNURB at the command line to convert of your building top polygons to a Non Uniform B-Spline (NURBS) Polysurface.
The original polygons will remain selected (in yellow) after the command has finished. You can hit the delete key to get rid of them.
Select your terrain surface and repeat the two steps described above to turn your terrain into a NURB and delet the original polygon mesh.
Now we will create curves around the edges of these new building top surfaces, and project them onto the terrain surface.
Select the building top surfaces and use the DupBorder command to make a new set of curves that follow the borders of the building tops.
Use the Project command to project these border curves to your terrain surface. Make sure to flip the DeleteInput option to Yes so that you will not have an extra set of building outlines in your model.
When this command completes, you will have a new set of 3D courves in your model that you can put into your Building_Contours Layer.

Create Terrain Solid with Skirt

In this phase, we will take our terrain surface, and project its edge down to model the vertical sides of our foam model. This is simoar to what we did with building tops.

Select the terrain surface and use the DupBorder command to make a new object that is the border of the polysurface.
Use Project to project this border curve to your 12"x12" rectangular mesh. Make sure to flip the DeleteInput option to Yes.
From the surface menu choose Surface>Extrude Curve>Straight to extrude the 2d border projection to create a fence that rises above the terrain surface. Be sure that the Cap option is set to Yes so that the new extrusion will be capped on the bottom.
Use the Trim command, select your fence as the surface to trim, choose the 3d surface border (not the surface) as the cutting object.
After trimming, you should hit the escape key to leave the trim command, which is witing for you to select the next thing to trim.
You can delet the 12x12 surface now, that we created at the begining of this process.
Use Solid>Create Solid to join the terrain surface with its rectangular base.
Select this new Solid and move it to the Terrain layer that you created.

Export Data as STEP Files

Rhino does not know how to control our CNC milling machine. So we need to create some files that will be understood by soem other software that does know how to drive the mill. We use a program called masterCAM for this. This is covered in another step by-step list linked to Workflow for Automated Milling of Site Models. SO our last step in this Rhino workflow is to create 3 files that we can open in MasterCAM to define our geometry.

Select each of the terrain solid, the rooftop surfaces, and the extrusion intersection curves and export to 3 individual step files.


	Geographic Information Systems (+/-) Geographic Information Systems in the Design School Getting Started With ArcGIS at the GSD GIS Software Manuals GIS Courses at the GSD Links for GSD GIS Fans Data Resources (+/-) GIS Data Resources Understanding GIS Data, Metadata and Schema GSD Data Collection About Census Data US Census Data: 2000-1970 from Geolytics US Business Directory Digital Elevation Models Sources of Geographic Images Data Handling (+/-) Understanding GIS Data, Metadata and Schema ArcMap 101: Exploring Peoria Data Geotagging Site Photos Beginning a GIS Database Concepts of Geographical Referencing Systems Why Don't My Layers Line Up? AKA: ArcMap Projections Tutorial Georeferencing Scanned Maps and CAD Data Converting GIS Layers to DXF Geocoding Clipping an Ocean Polygon A Random Tutorial Effective Cartography (+/-) Elements of Cartographic Style Basic Cartography in ArcMap Mapping with Nominal-Class Data Mapping with Quantitative Data Mapping Census Data Tutorial Analytic Techniques (+/-) Spatial Models in Scholarship and Decision Support Guidelines for Documenting Models Setting up a Geoprocessing Environment A Development Buildout Model Real Estate Tutorial Mastering Relational Procedures in ArcMap Vector GIS Procedures in ArcMap (Allston) Vector GIS Procedures in ArcMap (Transit) Raster GIS Procedures in ArcMap (Earthshelter) Raster GIS Procedures in ArcMap (Winter Olympics) Processing the Census Transportation Planning Package Classifying Satellite Images Designing for Visibility Studying Urban View Corridors Evaluating Development Scenarios Reverse Engineering New Urbanism Topographic Modeling in 3D (+/-) Conceptualizing and Modeling Sites Good Site Model Structure in Sketchup Basic Terrain Modeling (ArcGIS) Experimenting with Massing Scenarios in SketchUp Beginning a 3d Site Model in SketchUp Experimenting with Zoning Dimensional Regulations in 3d A rough Understanding of 3D Site Context with ArcGlobe Graphics and Animation in ArcGlobe Workflow for Automated Milling of Site Models Interchanging 3D Data between ArcGIS and 3dStudio Topographic Modeling in FormZ (+/-) FormZ 101: A Field of Dreams Modeling Terrain with Contours and Surfaces (formZ) Modeling Surfaces with Mapped Images (formZ) Analytical Graphics from 3-D Site Models (formZ) Metropolitan Scale 3d Models (+/-) The Boston Virtual City Collective Retrieving Scenarios from the Metropolitan Model Repository Creatning Historic and Future Scenarios Studying Urban View Corridors Integrating Administrative CAD Data, GIS and Google Earth Export NYC Data to Sketchup
				Preparing Site Models for Milling This document lists a set of steps for preparing a site model containing a terrain surface and extruded objects for milling on the GSD's Computer Numericly COntrolled (CNC) Router. This page is supplemental to the page Workflow for Automated Milling of Sites. We assume you have a sketchup model containing a terrain mesh, and tthe flat tops of the extruded objects, at the correct elevation above the terrain. Import Model to Rhino, Scale and Shift to fit in Milling Material Our terrain model starts out quite large, probably more than 100 feet in extent, but we need to scale it so that it fits on a relatively small piece of foam.We use Rhino as a tool for transforming the model -- scaling and shifting and rotating it into a coordinate space that the milling machine will be comfortable with. Create new Rhino file: Large Objects / Inches Import sketchup file. Select all, and use Edit->Group to group everything Choose Transform>Scale3d or Type Scale into the command window - choose origin of rhino model (in middle of grid). With Snaps on, choose Surface->Plane->Corner to Corner to create a rectangular mesh 12" x 12" with one corner at the origin of your model. Use the Arrow tool to Shift the the model into the box. Use Transform>Rotate to rotate model to fit in the box. Scale and shift and rotate again as needed to fit into the box with at least a half inch margin around the work. If zooming/panning gets very tired, use View>Viewport Properties to set camera and target to be near the origin. In one of your elevation viewports, move the model up so that the top of the model is just below 2 inches. Hopefully you still have an inch of material below, so that the foam won't warp or tear loose during the milling job. Ungroup Adjust Precision of the Rhino Model Many of the representations in rhino are curves that are parmetrically defined, as opposed to lines which have explicit begining and end points, and whose intersections can be calculated fairly easily. Being curve-oriented is an advantage for some things, but it is a bit less exact. One thing that comes up when bringing in a very large site model and then scaling it down to an 8 insh square is that Rhino adopts a faily low precision when it opens the large model. Think of precision as the snapping tolerance used by the automated operations of the program itself. But when we get the model down to something small, we should adjust the precision accordingly, or else there will be problems -- particularly in the step where we have to connect up several surfaces to create a closed solid. Go to Tools>Options>Units and set your Tolerances as follows: Absolute: 0.0001 Relative: 0.001 Angle: 0.001 Convert the Rooftop Polygon Surfaces to NURBS and Drape Terrain INtersection Curves Rhino and Mastercam are surface oriented, and many of their operations are most happy when surfaces are expressed as continuos curve funcetions known as Non-Uniform B-Splines or NURBS. IN the next sequense of steps we will use the layer manager subsystem of rhino to put our buiklding tops on a new layer, and we will use a transformation tool to convert the polygons that are our rooftops to NURBs, and finally we will create outlines of these surfaces and project them onto the terrain surface. These lines will represent the place where the building meets the grouns and will be used to tell the router exactly how to cut around the buildings. Select the Building tops. These have probably been grouped so that they will all select at the same time. Use Edit>Layers>Edit Layers to open the Layer Manager. right click to reate a new layer for your tops. While we are in the layer manager, create a new layer for the Building_contours and another for your Terrain. Right click the Tops layer and use Change Object Layer to place all the building tops (selected) into this layer, and click the lightbulb to hide these tops for now. Type meshtoNURB at the command line to convert of your building top polygons to a Non Uniform B-Spline (NURBS) Polysurface. The original polygons will remain selected (in yellow) after the command has finished. You can hit the delete key to get rid of them. Select your terrain surface and repeat the two steps described above to turn your terrain into a NURB and delet the original polygon mesh. Now we will create curves around the edges of these new building top surfaces, and project them onto the terrain surface. Select the building top surfaces and use the DupBorder command to make a new set of curves that follow the borders of the building tops. Use the Project command to project these border curves to your terrain surface. Make sure to flip the DeleteInput option to Yes so that you will not have an extra set of building outlines in your model. When this command completes, you will have a new set of 3D courves in your model that you can put into your Building_Contours Layer. Create Terrain Solid with Skirt In this phase, we will take our terrain surface, and project its edge down to model the vertical sides of our foam model. This is simoar to what we did with building tops. Select the terrain surface and use the DupBorder command to make a new object that is the border of the polysurface. Use Project to project this border curve to your 12"x12" rectangular mesh. Make sure to flip the DeleteInput option to Yes. From the surface menu choose Surface>Extrude Curve>Straight to extrude the 2d border projection to create a fence that rises above the terrain surface. Be sure that the Cap option is set to Yes so that the new extrusion will be capped on the bottom. Use the Trim command, select your fence as the surface to trim, choose the 3d surface border (not the surface) as the cutting object. After trimming, you should hit the escape key to leave the trim command, which is witing for you to select the next thing to trim. You can delet the 12x12 surface now, that we created at the begining of this process. Use Solid>Create Solid to join the terrain surface with its rectangular base. Select this new Solid and move it to the Terrain layer that you created. Export Data as STEP Files Rhino does not know how to control our CNC milling machine. So we need to create some files that will be understood by soem other software that does know how to drive the mill. We use a program called masterCAM for this. This is covered in another step by-step list linked to Workflow for Automated Milling of Site Models. SO our last step in this Rhino workflow is to create 3 files that we can open in MasterCAM to define our geometry. Select each of the terrain solid, the rooftop surfaces, and the extrusion intersection curves and export to 3 individual step files.