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/, many users wish to use their own 3D models 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 represents objects by approximating their surfaces using polygon meshes. Procedural Solids represents objects by first using primitives (cylinders, prisms, pyramids, spheres, cones) and then constructing the object by means of operations such as Boolean operations on sets (union, intersection, and difference) as well as geometric transformations of those sets.
Obtaining 3D models
There are many places on line to get free 3D models or to buy models. Here are some resources:
You can import many of these models directly into STK if they are in glTF or COLLADA model format. Some models need editing 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. In house, AGI engineers 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. This tutorial is part of an FAQ called "
How to Convert CAD Models for Use in STK."
Another free modeling utility is
SketchUp. It's fairly easy 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. STK uses meters.
• Make sure that the model is axis aligned properly. Generally, STK's X axis is the velocity axis. The Z axis points toward 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. These will increase the polygon count and rendering time without adding analytical value.
• Remove all two-point polygons.
• Merge small polygons less than 10mm.
• Separate out, into its own layer, any geometry 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 (i.e., 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. In house, AGI engineers 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 you take steps to reduce the polygon count. You can do this by removing all internal parts before the conversion. Creo Parametric calls this "Shrink Wrapping." Other apps may have something similar.
• To the extent possible, remove all external parts like nuts and bolts .
• Follow this rule of thumb: 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), you can convert it to an STK MDL model (*.mdl) using AGI's proprietary utility, LwConvert. To obtain the utility, follow these steps:
- Go to the downloads page on the AGI website.
- Select the "Other" tab and locate the download for Lightwave Converter in the list.
- The download zip includes the utility and a LwConvert "Read me" text file . All documentation for LwConvert is available from within the utility.
