How to convert CAD models for use in STK

Information

 
QuestionHow do I convert a CAD file for use in STK
Answer

Overview of 3D Models


3D models add realism to STK by depicting objects as they truly appear. While AGI has a plethora of models available at www.agi.com/models, many users wish to use their own CAD based model in STK. To use your own model in STK, the model needs to be converted to a glTF model (*.gltf, *.glb), a COLLADA model (.dae), or an STK MDL model (*.mdl). If using the STK MDL model, the CAD model needs to be converted to a LightWave model (*.LWO), then converted to a STK MDL model (*.mdl).

To learn more about the different model formats supported by STK, please see the STK Help at: STK Help > Getting Started > Customize 2D & 3D Graphics > 3D Graphics (Globe) Window > Using Models
 

Converting 3D Models


To learn how to convert a model for using in STK, please see the attached tutorial. The tutorial utilizes a free 3D modeling program called Blender, which is one of many tools that could be used to convert CAD models for use in STK. 

The attached tutorial files provides a walk-through of the following list of materials to convert a satellite model in STL format to COLLADA format with a full set of articulations:
 

  1. Blender Fundamentals
    1. Recommended Settings and Basic Controls
    2. Working with Primitives
    3. Importing Model Files
  2. Modifying and Preparing Models for Use in STK
    1. Component Scaling
    2. Axes Alignment
    3. Component Alignment
    4. Component Parenting
    5. Shading
    6. Solar Panel Groups
    7. Sensor Attach Points
  3. Materials and Textures
    1. Adding Materials and Colors
    2. Adding Textures with UV Mapping
  4. Exporting and Articulation File Creation
    1. Exporting COLLADA File
    2. Creating Ancillary Files
  5. Implementation in STK

Every CAD conversion is different and depends on the user's requirements for the geometry and how accurate the materials need to look. Not every step in the tutorial will be necessary for each model. 
 

Best Practices


Before importing the CAD model into Blender, there are a few things to consider. The biggest issue is to have the data prepped for export. Here are a few guidelines to consider:
  1. Remove spaces from the names of files
  2. Any internal geometry should be removed because it’s not going to be seen.
  3. All small parts such as nuts, bolts, washers, bolt holes, wiring should be removed. They unnecessarily add to the polygon count once converted.
  4. After the edits, the CAD model should be saved in its native file format with a different name and then exported to an *.stl format.
  5. Any parts that will need to be articulated in STK should be saved as a separate file.
If you don’t have the software, you could send a request back to the CAD engineer and request the edits.

Depending on the detail of the original CAD file, the converted model file could still have so many polygons that it won't load into STK. While there is a no limit to the number of polygons your model can have, other than the hardware of your machine, there is is a limit to the number of polygons per Node/Component/Layer. If the exported STL file is larger than 10MB, or roughly 90,000 polygons, then it should be broken up into at least a couple of assemblies or it will not load into STK. The reason for this is that the XML reading library libXML, which is used by the COLLADA DOM, has a limit of 10 million characters within any xml tag.

This does not mean that you cannot have any file larger than 10MB, only that each component/assembly/node within the COLLADA file cannot be larger than 10MB. You can have as many components/assemblies/nodes as are needed.
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