Introduction

With 3D GIS data becoming more common in industry, the importance of game engines is increasing for

creating high quality geographic visualizations and interactive simulations. Unity and Unreal Engine are

two game engines well positioned for these needs. This document compares the two engines to help

evaluate their suitability for GIS visualization and simulation tasks. The workflow for creating animations

and interactive simulations of models generated by CityEngine, Esri’s procedural modelling software,

will be explored.

Unity and Unreal Engine

The game engines provide tools for animating objects in the scene along with a physics engine, which

can be used to simulate behaviour such as object collision, gravity, and character movement.

The similarities diverge when looking at customizing the engine to create new gameplay elements. In

Unity, C# and JavaScript are the supported programming languages, while Unreal requires either using a

node based visual editor called Blueprints to link engine functionality or programming in C++.

Although Blueprints provide a way to create custom behaviour without programming, the overall

learning curve of Unreal Engine is steeper than Unity due to the user interface being more complex.

Unreal Engine called Unreal Studio, which provides the ability to import data directly from supported

design software, is currently in beta release. Recent releases of CityEngine support exporting data into

Unreal Studio’s Datasmith file format. A CityEngine Unreal Studio template is also available that contains

materials that translate the CityEngine material attributes to Unreal materials.

Comparison

The 3D model export from CityEngine to the game engines can be time intensive, especially if the

process is executed frequently due to model updates. The table below summarizes a sample export of

over ten thousand tree models generated in CityEngine to the game engines.

The import process into Unreal Studio was much quicker because instanced meshes are supported with

the Datasmith export. This instancing works by referencing duplicate geometry instead of exporting

every instance individually.

The export of 3D buildings was also timed to evaluate the performance using models that aren’t suitable

for instancing due to non-repeating textures and geometry. As expected, there was no speed

improvement for Unreal Studio over Unity. However, it was surprising how much quicker the FBX export

executed compared to the Datasmith export.

Unity Asset Store

Unity provides an online store where assets can be purchased or downloaded for free. These assets

include 3D animations, models, shaders, and scripts.

Unreal Marketplace

The Unreal Marketplace can be used to purchase assets such as animations, characters, music, textures,

materials, and plugins. Some of the assets are also available for free download.

Comparison

The ability to easily find and download assets can be incredibly useful to save time when working on a

3D project. Unity seems to have more assets available for download. For example, the Unreal

Marketplace returns 11 results when searching with the keyword “traffic”, while Unity returns 392

Imported models can be explored interactively by adding a first or third person game object to the

scene. Alternatively, the built-in animation system can be used to move the camera through the scene

for a fly through.

In Unity, there is no built-in mechanism for saving the output of the game view to a video file. However,

free packages are available to download from the Unity Asset Store to accomplish this task.

For simulating character movement on a surface, a Navigation Mesh or NavMesh can be built based on

imported geometry such as a model of sidewalks or paths. Once characters are configured as NavMesh

Agents and assigned a script that determines the destination goal, they will be able to find the shortest

path on the NavMesh while avoiding obstacles.

Unreal supports building NavMeshes for character movement. Once a character is assigned an AI

Controller created with either Blueprints or C++, it will be able to navigate to destinations on the

NavMesh.

Comparison

Creating a simple character controller can be accomplished in both Unity and Unreal, though more steps

In Unity, this simply involves inserting a character controller included with the engine into the scene.

Animating cameras and objects in the scene is accomplished in both engines by creating keyframes in an

animation panel. However, Unreal Engine does have the functionality built-in to save videos of game

output, while in Unity this must be programmed or found in the Unity Asset Store.

For simulations such as crowd movement, both engines can build navigation meshes using imported

Based on the pricing model, Unity Personal is the best choice for projects where a splash screen is

acceptable and company revenue is less than $100 000. Unity Plus or Unity Pro are required as company

revenue increases.

Unreal Studio has a royalty free pricing model, with a cost of $49 per month when purchased with an

annual subscription.

Comparison

For creating interactive simulations, Unreal Engine can be used for free when using the FBX import

workflow provided no revenue is generated from the created simulation. However, because the

CityEngine to Unreal FBX workflow is not recommended due of the performance benefits of using

Datasmith, comparing Unreal Studio to Unity is more useful. The $49 a month cost of Unreal Studio is

competitive as it falls between the free and $125 monthly costs of the different versions of Unity.

Conclusion

Unity and Unreal Engine are very useful tools for visualizations and simulations of GIS data.

Experimenting with both engines before purchasing a license is recommended as they can be

downloaded for free to evaluate.