Description
Virtual Orrery and Real Time Rendering
1 Overview and Objectives
An orrery is a model of the solar system that mechanically replicates the orbital motions of the
planets around the sun. Detailed orreries also replicate the orbits of planets’ satellites around
their primaries. As with many other wonderful mechanical trinkets, orreries have mostly lost their
significance with the advent of computer simulations and graphics.
Your job in this fourth assignment of CPSC 453 is to develop a virtual orrery that animates
and renders the relative motions of the Sun, Earth and Moon against a starry backdrop. This task
allows you to assemble many of the things you’ve learned in the course into a final rasterization
assignment using OpenGL (note that the last assignment in the course will use ray tracing for rendering and not OpenGL). You will need to write C++ and OpenGL shader code to implement many
of the concepts learned in class, including geometry specification, coordinate systems, reference
frames, interactive input, composition of 3D transformations, model and view transforms, texture
mapping, shading, and real-time animation.
Source code for a boilerplate C++/OpenGL application is provided for you to use as a starting
point, though you may create your own template if you prefer. The boilerplate provides you with
a spherical camera implementation and basic shading for starting your orrery. The camera can be
zoomed using the scroll wheel and rotated by holding the right mouse button and dragging the
mouse.
2 Due Date
November 28th at 11:59 PM
3 Programming Assignment
There are a total of four parts to this programming assignment with an additional requirement for
integration and controls. This assignment is worth a total of 20 points, with the point distribution
as indicated in each part, and an additional possibility of earning two “bonus” designations. Note
that the bonuses may require going beyond what is presented in the lecture and tutorial components
of the course and may require student initiative to find online resources to complete successfully.
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3.1 Part I: Sphere and Texture Coordinates (4 Points)
Starting from the initially provided boilerplate code, or any template that you may have created
during this course, write a program that will generate triangle geometry to approximate a threedimensional unit sphere. There may be several good ways to do this. One possibility is to write a
C++ function that generates triangles from a parametric or other representation of a sphere (or an
ellipsoid created as a surface of revolution) and fills a vertex array with their vertex positions. For
your sphere, you must also generate normals for each vertex to be used in shading calculations later
and texture coordinates, to apply textures to your celestial bodies. Create four different spheres in
your scene, one for the Sun, Earth, Moon and an additional one to encompass the entire scene for
the starry backdrop. Texture these spheres using code similar to what was provided in assignment 2
(Note that you may simply copy and paste code from Assignment 2 if you like). To find the textures
for your celestial bodies feel free to download the images from one of the following sources:
1.http://www.solarsystemscope.com/nexus/textures/
2.http://planetpixelemporium.com/index.php
3.http://www.shadedrelief.com/natural3/pages/textures.html
Don’t worry about lighting or shading at this point – those will come later.
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3.2 Part II: Transformation Hierarchy (4 Points)
Define your “world” reference frame in terms of the Solar System, with an origin located at the
centre of the Sun. Organize your objects explicitly or implicitly so that the Earth’s position can be
described relative to the Sun, and the Moon’s relative to the Earth.
Position and scale your celestial bodies so that their relative sizes are reasonable in your virtual
scene. Encode the orbital inclination and axial tilt of the bodies as rotations in your transformation
hierarchy. Feel free to exaggerate the orbital inclination of the Earth so that it’s obvious in your
scene.
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3.3 Part III: Shading (4 Points)
Introduce a point light source into your scene, positioned at the centre of the sun. In OpenGL,
this usually just takes the form of a uniform vector variable in your shader. This will allow you
to calculate a light direction vector for your lighting equation. You will also need surface normals
which, like texture coordinates, can be stored and retrieved as vertex attributes or computed in the
vertex shader. Program the fragment shader to apply a shading model (Phong Shading) to your
objects. The Sun itself naturally needs no shading: it emits the light that illuminates your other
objects. Apply a diffuse reflection model for the Earth, and the Moon so that the side facing away
from the Sun is dark. Add specular and/or ambient components as you desire to make your scene
look as nice as you can. Do not shade the Sun or the starry backdrop with diffuse or specular
reflection.
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3.4 Part IV: Animation (4 Points)
Now that you have all your celestial bodies rendered beautifully with textures and shading, it is
time to make them move. Animate the axial rotation of each body and the orbital rotation of the
Earth,and the Moon about their respective primaries. Make both the axial and orbital rotation
periods of each body reasonable. A rate of one day per second of animation time, or even faster is
appropriate. Provide at minimum a means for pausing and restarting your animation, and if you’d
like, add the ability to adjust the animation speed. Note that each body has an axial tilt, meaning
that its axis of rotation is not perpendicular to its orbital plane. The Moon has an orbital inclination
with respect to the Earth’s equator, meaning that its orbital plane is tilted from the Earth’s axis
of rotation. The Earth also has an orbital inclination with respect to the Sun’s equator, and you
may choose whether you prefer to tilt the Sun’s rotational axis or the Earth’s orbital plane for your
orrery. You must capture axial tilts and orbital inclinations in your animation to receive full credit
for this part. You may ignore orbital eccentricity and have the bodies follow circular orbits. The
red arrows in the diagram denote movement of the Earth around the sun. The green arrows denote
the movement of the Moon around the Earth.
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3.5 Integration and Control (4 Points)
Ensure that your program does not produce rendering anomalies, or crash, when animating your
scene. Efficiency is important too! Programs that fail to clean up resources or generate excessive
amounts of unnecessary geometry may bog down the system or eventually crash, and will not
receive full credit.
3.6 Bonus Part I: Realistic Orrery (4 Points)
The first possibility is to use some advanced texture mapping techniques, combined with the programmability of the fragment shader, to create an Earth that looks as realistic as possible. Here are
some suggestions for what you might do:
1.Normal or bump mapping: shade the mountains and valleys to stand out.
2.Specular mapping: the oceans may look better if they were shinier than land masses.
3.Cloud texture(s): animate clouds that move over the Earth’s atmosphere.
3.Day/night textures: use a dark texture with city lights for the side away from the Sun.
4.Shadows: simulate the effects of solar and lunar eclipses.
3.7 Bonus Part II: Complete Orrery (4 Points)
The second possibility of earning a bonus is to flesh out your virtual orrery to include all the planets
of the solar system and as many of their satellites as you can find information about. Add the ability
to:
1.To slow down or speed up the animation to appreciate slow or fast objects.
2.To centre the camera on different planets to appreciate those perspectives.
3.Incorporate orbital eccentricity (elliptic orbits of the celestial bodies).
4 Submission
We encourage you to learn the course material by discussing concepts with your peers or studying
other sources of information. However, all work you submit for this assignment must be your
own, or explicitly provided to you for this assignment. Submitting source code you did not author
yourself is plagiarism! If you wish to use other template or support code for this assignment, please
obtain permission from the instructors first. Cite any sources of code you used to a large extent for
inspiration, but did not copy, in completing this assignment.
Please upload your source file(s) to the appropriate drop box on the course Desire2Learn site.
Include a “readme” text file that briefly explains the keyboard controls for operating your program,
the platform and compiler (OS and version) you built your submission on, and specific instructions
for compiling your program if needed. In general, the onus is on you to ensure that your submission
runs on your TA’s grading environment for your platform! It is recommended that you submit a
test assignment to ensure it works on the environment used by your TA for grading. Your TAs are
happy to work with you to ensure that your submissions run in their environment before the due
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date of the assignment. Broken submissions may be returned for repair and may not be accepted
if the problem is severe. Ensure that you upload any supporting files (e.g. makefiles, project files,
shaders, data files) needed to compile and run your program. Your program must also conform
to the OpenGL 3.2+ Core Profile, meaning that you should not be using any functions deprecated
in the OpenGL API, to receive credit for this part of the assignment. We highly recommend
using the official OpenGL 4 reference pages as your definitive guide, located at:https://www.
opengl.org/sdk/docs/man/.
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