How do I use my own 3D model in STK?

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QuestionHow do I use my own 3D model 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 3D model in STK. To use your own model in STK, the model needs to be a glTF model (*.gltf, *.glb), a COLLADA model (.dae), or an STK MDL model (*.mdl).
 

Types of 3D Models

There are two main categories of model file types: Polygonal and Procedural Solids. Polygonal modeling is an approach for modeling objects by representing or approximating their surfaces using polygon meshes. Procedural Solids is an approach for model objects by representing primitives (cylinders, prisms, pyramids, spheres, cones) and then constructing the object by means of operations (Boolean operations on sets: union, intersection and difference, as well as geometric transformations of those sets).
 

Obtaining 3D Models

There are many places online to get free 3D models or to buy models. Here are a couple of free resources: Many of these models can be directly imported into STK if they are in glTF or COLLADA model format. Some models need to edited to appear properly in STK, regardless of format. See the next section, Editing 3D Models, for more details.
 

Editing 3D Models

If you need to edit a 3D model, there are commercial and free modeling packages available. While we don't recommend any particular package, in-house we use Blender (Open Source),  MODO by Foundry, and LightWave by NewTek

AGI engineers have created a tutorial on converting CAD files through Blender for use in STK. You can find this tutorial on our FAQ: "How to convert CAD models for use in STK".

Another free modeling utility is SketchUp. It's a fairly easy utility to use and will natively create COLLADA models, which STK supports.

General notes on editing 3D models:

  • Make sure that the model is scaled properly. 
  • Not all modeling apps use the same internal units of measurement. The MDL format uses meters.
  • Make sure that the model is axis aligned properly. Generally STK's X axis is the velocity axis. The Z axis points towards or away from nadir, depending on which model type you are using.
  • Make sure all the polygons are facing the correct direction (to ensure the material textures are pointed outward).
  • Remove any internal components, rivets, or unnecessary elements. Things like rivets or internal components will increase the polygon count and rendering time, without adding analytical value.
  • All 2 point polygons should be removed.
  • Merge small polygons less than 10mm.
  • Separate out any geometry into its own layer that you will want to articulate later in STK. Search the FAQs for “Articulations” for further directions.

Converting 3D Models

You may have a 3D model that you want to use in STK, but it is not in a format that STK supports (glTF model, COLLADA model, or STK MDL model). You will need to convert the model into one of these formats to use with STK. 

There are free or commercial modeling packages available to convert 3D models. While we don't recommend any particular package, in house we use PolyTrans and Blender (Open Source).
 

General Notes on converting 3D models:

  • CAD models (from Creo Parametric, Unigraphics, Solid Works, etc.) may have very high polygon counts after the model is tessellated. These models will render slowly in STK unless steps are taken to reduce the polygon count.
    • This can be done by removing all internal parts before the conversion. Creo Parametric calls this "Shrink Wrapping". Other apps may have something similar.
  • All external parts, like nuts and bolts, should also be removed as much as possible.
  • A rule of thumb is don't convert more model than you absolutely need.
  • Make sure that your export units are in meters.

Converting From a Lightwave format

If you have a LightWave model (*.LWO), then it can be converted to an STK MDL model (*.mdl) using AGI's proprietary utility, LwConvert. 

Follow these steps:
  1. Download LwConvert, which can be found on the AGI website here
  2. Then select the "Other" tab and locate the download for Lightwave Converter in the list.
  3. If you don't see it at first, uncheck all the "Type" filter buttons and then check the "Free" button.
  4. After the page refresh, look for "Lightwave to MDL Utility" and click on "Download". All documentation for LwConvert is available from within the utility.
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