Modelling and animating a solar system using Real3D v3.5

Introduction

Release note:

As the first issue on this was first released as a zipped file, some references to files will no apply. I have not had the time to go through this whole tutorial again, so if you find such a reference, please email me at kpetter@c2i.net, and I will mail you any missing files by hand. This is the first tutorial I wrote, so it isn't all that good. Also, this tutorial is not scientific accurate, to say the least.

Aim:

This small tutorial will guide you through the steps needed to create a planet orbiting a star, which also contains a moon orbiting the planet. When done you will have learned how to create faked sharp terminators on planets (as the current release of Real 3D does not support it directly), control object by different animation methods, and some basic use of skeletons to control the objects. Also, a way of producing faked 'radiosity' (actually albedo value) will be shown.

Who is it for:

It is best if you have a little experience with Real3D before going on with this. At least the understanding of the hierarchical way Real 3D works, and some basic understanding of the Real 3D standard user interface is required. You don't have to be an expert though, as most things are explained. However, some things have been left out, to encourage you to study the manual... (good excuse, huh?) maybe even come up with better ways of doing this.

Features:

The orbits are animated using PATH methods. Additional ROTATION methods to rotate the bodies.
Relative and correct scale ratios are presented, but have been overridden for better visualization.
Animated (autopoint type) 'radiosity', to make the earth light up unlit parts of the moon, and vice versa.
Animated (autopoint type) transparancy map, so the light can shine through the surface of the earth, still casting full shadows.
Simple texture maps; earthcol.iff, mooncol.iff, transpmap.iff. Kept small, find better maps somewhere on the web.
Full eclipses and partial eclipses will/can happen at some point in the animation, depending on time scale.

Modelling time, and some easy animating

Preperations:

Start Real3D with no default lights, no materials, and no objects (or hit 'File/Project/New', and delete the materials).
The default 0.1 meter sized grid will work fine.
It might also be a good idea to set 'Settings/Creation/Qry. Level Name' since we for all levels will have appropriate names.
Be sure that the RPL-script is in the macros directory, and you might test it as well. It should generate an ellipse with the left focus-point at excactly 0,0,0.

Create some materials:

Create a material called 'earth-col' with 'EarthCol.iff' as a map. Tile x on and -1. Grade x and grade y could be applied. Set the Angle Scope handler with a = -1.1, and b = 0. Rest is default.
Create a material called 'moon-col' with 'MoonCol.iff' as a map. Tile x on and -1. Grade x and grade y could be applied. Set the Angle Scope handler wih a = -1.1, and b = 0. Rest is default.
Create a material called 'transp-map' with 'TranspMap.iff' as a map. Color off, and transp map on. Grade x and Egde x to prevent restarting. Tiling should be off. Rest is default.

Then we need to create a working hierarchy for the earth body:

Change the root name to 'solar-system'
In this, create a level called 'system-earth'
In this, create a level called 'planet-earth'
In this, create a level called 'rotating'
In this, create a level called 'parts'
Step one up, to 'rotating', and create a level called 'ROTATION' to mark it as a future method holder
Step one up, to 'planet-earth', and create a level called 'radiosity'
In this, create a level called 'SKELETON' to mark it as a future method holder
Step up to 'planet-earth' and create a level called 'transp', and set the mapping flag
Enter this, and create a level called 'SKELETON' to mark it as a future method holder

The moon is also a part of the earth going around the sun, so:

Step up to 'system-earth' and create a level called 'system-moon'
In this, create a level called 'moon-moon' (for Jupiter one could have created moon-io, moon-europa etc)
In this, create a level called 'rotating'
In this, create a level called 'parts'
Step one up, to 'rotating', and create a level called 'ROTATION', to mark it as a future method holder
Step one up, to 'moon-moon', and create a level called 'radiosity'
In this, create a level called 'SKELETON' to mark it as a future method holder
Step up to 'moon-moon' and create a level called 'transp', and set the mapping flag
In this, create a level called 'SKELETON' to mark it as a future method holder
Step up to 'system-moon' and create a level called 'PATH' to mark it as a future method holder
Step up to 'system-earth' and create a level called 'PATH' to mark it as a future method holder

Okay, let us check what we have. Your working hierarchy should look like this:

solar-system system-earth planet-earth rotating parts ROTATION radiosity SKELETON transp(T) SKELETON INV KINEMATIC system-moon moon-moon rotating parts ROTATION radiosity SKELETON transp(M) SKELETON PATH PATH

Inner parts are modelled first, so lets create the moon:

Enter the 'parts' level somewhere inside the 'moon-moon' level.
Take a top view, and create a sphere about 0.1 m in diameter in the center (0,0,0).
Create a spherical mapping with the moon-col map.

Make the moon rotate about its axis:

Enter the ROTATION level somewhere in the moon-moon level.
Hit 'a' while this level is selected, select ROTATION, and set frequency to 27.
Take a front view, and create an axis from y=-0.2 to y=0.2. The direction is important.
Go back to and select the whole 'rotating' level, and rotate the object, say, 10 degrees (our moon isn't actually tilted this way, this is just an example), still from the front view.

Put the moon into an orbitlike path:

Go to the 'PATH' level somewhere in the moon-moon system and take a top view.
Hit 'z' and select the ellipse macro, with 0.5, 0.3 and moon-orbit as its input.
Select the 'PATH' level, hit 'a', and select PATH. Set frequency to 27.
Go back and select the 'rotating' level, and move its objects to the rightmost quadrant of the ellipse, which should be at about x=0.65.
Take a top view and zoom close to the moon. Enter the 'transparency(T)' level.
Create a parallel mapping using the transp-map. Click first in the upper left corner, and then in the lower right. Make sure it covers the moon excactly.
We will rotate the mapping later to get it properly aligned.

Let us test what we have so far:

Bring up the animation window, use a high frame count, say 5000.
Play the animation with a top view. You'll notice that the moon rotate one time for each orbit, and this is just like real life for our moon. If you change the frequency in the rotation level to a much higher number, say 600, you will get a more earthlike orbit and rotation (though this is by far the correct values). If we had used a perfect circle (eccentricity=0), then it would have been possible to use a DIRECTION method instead of a PATH method (provided the moon had only one rotation per orbit), and get rid of the ROTATION method. But since the orbit we use in this case is slightly elliptical, we have to use both PATH and ROTATION methods. This is also like the real life; the moon will actually show us some (about 5%) of the 'darkside' during an orbit. The more the elliptical the orbit path, the more of the darkside will show. Also, remember I said something about using a TRANSFORM method to control the speed of the orbiting body; if we had used DIRECTION here, the TRANSFORM method would have affected both motions the DIRECTION controls.
Take a front view, and play. Here you'll see that the axis is constantly tilted during the animation. As you may know, the earth is tilted quite a bit, and it is this tilt that gives us seasons.

We cannot complete the animation parts of the moon until its parent body is done, the earth:

Enter the 'parts' level somewhere inside the 'planet-earth' level.
Take a top view, and create a sphere about 0.2 m in diameter in the center (0,0,0) so that it is twice the size of the moon (which is just about the case with the earth-moon system).
Create a spherical mapping with the earth-col map.

Make the earth rotate about its axis:

Enter the ROTATION level somewhere in the planet-earth level.
Hit 'a' while this level is selected, select ROTATION, and set frequency to 365 as we have roughly 365 days in a year.
Take a front view, and create an axis from y=-0.2 to y=0.2. The direction is important.
Go back to and select the whole 'rotating' level, and rotate the object, say, 20 degrees (it's actually more, but this is an example), still from the front view.

Put the earth into an orbit like path:

Go to the 'PATH' level somewhere in the 'system-earth' level and take a top view.
Hit 'z' and select the ellipse macro, with 2.5, 0.05 and earth-orbit as its input.
Select the 'PATH' level, hit 'a', and select PATH. Set frequency to 1.
Go back and select the 'rotating' level, and move its objects to the rightmost quadrant of the ellipse, which should be at about x=2.625.
Take a top view and zoom close to the earth. Enter the 'transparency(T)' level. Create a parallel mapping using the transp-map. Click first in the upper left corner, and then in the lower right. Make sure it covers the earth excactly. We need to create this at this stage to keep the transparancy map properly aligned.

Now it is time to position the moon in respect to the earth:

Go to the 'system-earth' level, select the 'system-moon' level.
Take a top view and move this level from 0,0,0 to the center of the earth, which should be at about x=2.625.
Since we have already rotated the earth about 20 degrees, we now have to rotate the whole 'moon-system' level accordingly. Select this level and rotate it 20 degrees. However, not many moons have such a perfect inclination to the parent bodys' equator, so we can rotate it a little more, say, an additional 4 degrees. Try to keep this number small.

Advanced animation, adding position independent 'radiosity'

Okay, so much for the easy part... Now we are going to add some 'radiosity' to the animation in such a way that the sunlight that hits a body, gets reflected back out into space directed towards the sun. I originally wanted to do this with SKELETON and INV KINEMATIC animation methods with line parameters, but due to a bug (or change) in v3.5, I will have to do this in a completely different manner. Also, when using the skeleton primitive as a skeleton parameter combined with a locked IK offset, the result was not satisfactory. Because of that, I use a skeleton animation type, a normal line as the parameter, and animating the endpoints of the line with groups. There probably are even better ways to do this.

Create a spotlight controlled by a skeleton:

Enter the 'radiosity' level somewhere in the 'moon-moon' level.
Take a front view and create a spotlight from the moons center, pointing to 0,0,0.
Select the 'SKELETON' level, hit 'a', and change it to SKELETON animation type.
Enter the 'SKELETON' level, and create an axis from the moons center to 0,0,0. Set the protected flag for the line which shall act as a skeleton.
Enter the 'line' level, use 'Modify/Freeform/Divide to Groups', and set the upper value to 1, lower is default. It's probably a good thing to change the SIDE tags to 'moonline1' for the 'line', 'group', and 'group.1' objects instead of the rather cryptic number. This is something worth doing other times as well, to prevent dual tag numbers. It can't happen by itself, but it is a good habit, because this is an easy mistake if you are used to copying levels that contain groups, which should point to other objects. When doing a 'Render Hierarchy' in a 'debugging' situation, the bug is easier to spot.
Select the first group, hit 'B' to make it a level, and rename the level to 'outer'
Select the other group, hit 'B' to make it a level, and rename the level to 'center'. Set the protected flag for this level.
Enter the 'outer' level, and create a PATH method here, below the group. Set frequency to 27.
Find the 'moon-orbit' parameter curve in the 'PATH' level, which itself is in the 'moon-moon' level. Change the SIDE tag to 'moon-orbit'. Create a link object, cut the 'link' and paste it into the 'PATH' level inside the 'outer' level of the line. Make sure to set the protected flag of the link. I use to have the same name for the link and its object, but with a (l) to mark it as a link, so you may want to change its name to 'moon-orbit(l)'.
Go to the 'PATH' method in the 'system-earth' level, and copy the 'earth-orbit' parameter curve.
Go back to inside the 'line' level in the radiosity skeleton part. Create a 'PATH' method within the line.
Paste the 'earth-orbit' inside the 'PATH' method, and set the protected flag.

Have the moons transp-map be controlled by a skeleton in the same way:

Take a front view.
Enter the 'transp(T)' level somewhere in the 'moon-moon' level.
Select the 'transp-map(T)' mapping object, and rotate it around the moons center in such a way that it is in perfect alignment with the radiositys' skeleton line (having the same tilt, pointing towards 0,0,0).
Select the 'SKELETON' level, hit 'a', and change it to SKELETON animation type.
Enter the 'SKELETON' level, and create an axis from the moons center to 0,0,0. Set the protected flag.
Enter the 'line' level, use 'Modify/Freeform/Divide to Groups', and set the upper value to 1, lower is default. Change the SIDE tags to 'moonline2' for the 'line', 'group', and 'group.1'
Select the first group, hit 'B' to make it a level, and rename the level to 'outer'
Select the other group, hit 'B' to make it a level, and rename the level to 'center'. Set the protected flag for this level.
Enter the 'outer' level, and create a PATH method here, below the group. Set frequency to 27, and set the protected flag.
Find the 'moon-orbit' parameter curve in the 'PATH' level, which itself is in the 'moon-moon' level. Check that the SIDE tag is 'moon-orbit'. Creake a link object, cut the 'link' and paste it into the 'PATH' level inside the 'upper' level of the line. Make sure to set the protected flag of the link. Change its name to 'moon-orbit(l)'.
Go to the 'PATH' method in the 'system-earth' level, and copy the 'earth-orbit' parameter curve.
Go back to inside the 'line' level in the transp(T) skeleton part. Create a 'PATH' method within the line.
Paste the 'earth-orbit' inside the 'PATH' method, and set the protected flag.

The moon is now complete, and luckily the spotlight of the earth is a bit easier :-)

Enter the 'radiosity' level somewhere in the 'planet-earth' level
Take a front view and create a spotlight from the earths center, pointing to 0,0,0.
Select the 'SKELETON' level, hit 'a', and change it to SKELETON animation type.
Enter the 'SKELETON' level, and create an axis from the earths center to 0,0,0.
Set the protected flag for the line which shall act as a skeleton.
Enter the 'line' level, use 'Modify/Freeform/Divide to Groups', and set the upper value to 1, lower is default. Change the SIDE tags to 'earthline1' for the 'line', 'group', and 'group.1' objects.
Select the first group, hit 'B' to make it a level, and rename the level to 'outer'
Select the other group, hit 'B' to make it a level, and rename the level to 'center'.
Enter the 'outer' level, and create a PATH method here, below the group. Set frequency to 1.
Find the 'earth-orbit' parameter curve in the 'PATH' level, which itself is in the 'system-earth' level. Change the SIDE tag to 'earth-orbit'. Create a link object, cut the 'link' and paste it into the 'PATH' level inside the 'outer' level of the line. Make sure to set the protected flag of the link. Change its name to 'earth-orbit(l)'.

Have the earths transp-map be controlled by a skeleton in the same way:

The actual map is perfectly aligned for the earth, as the earth has an inclination of zero defined, so we won't do much here. However, for other planets, the inclination is not zero, and you must align the map properly, as we already did for the moon.
Select the 'SKELETON' level, hit 'a', and change it to SKELETON animation type.
Enter the 'SKELETON' level, and create an axis from the earths center to 0,0,0. Set the protected flag.
Enter the 'line' level, use 'Modify/Freeform/Divide to Groups', and set the upper value to 1, lower is default. Change the SIDE tags to 'earthline2' for the 'line', 'group', and 'group.1'
Select the first group, hit 'B' to make it a level, and rename the level to 'outer'
Select the other group, hit 'B' to make it a level, and rename the level to 'center'.
Enter the 'outer' level, and create a PATH method here, below the group. Set frequency to 1.
Find the 'earth-orbit' parameter curve in the 'PATH' level, which itself is in the 'system-earth' level. Check that the SIDE tag is 'earth-orbit'.
Creake a link object, cut the 'link' and paste it into the 'PATH' level inside the 'outer' level of the line. Make sure to set the protected flag of the link. Change its name to 'earth-orbit(l)'.

Final Comments:

One could use a TRANSFORM method to alter velocity along the orbit, but I don't know how to calculate it. You'd be better off choosing between 'radiosity' effect or the correct change in velocity. Since I don't know how to calculate it accurate enough, there is a picture below showing the typical TRANSFORM curves one could use for the orbits of the moon and the earth.
How to calculate (x,y). p1=(0.0,0.0), p3=(0.5,0.5), and p5=(1.0,1.0). For the earth p2 with x=0.25 then y=0.25-0.25*0.8(parameter)*0.05(eccentricity)=0.24. For the earth p4 with x=0.75 will then be 1-0.24=0.76. For the moon p2 with x=0.25 then y=0.25 -0.25*0.8(parameter)*0.3(eccentricity)=0.19. For the moon p4 with x=0.75 will then be 1-0.19=0.81. Note the shape of the curve. In the beginning the angle is less steep than in the midle of the animation. Thus we can see the angle as an indicator of velocity. Use 'Create/Controls/B-Spline Knot' to create the actual curve. See the figure below.

Note1:

If you are going to try to use a TRANSFORM method to control the speed of the main body (Earth), make sure that the TRANSFORM method is placed directly above the whole earth-systems PATH method, so that none of the above methods are affected. Therefore, one need to insert a TRANSFORM method directly above the moons PATH method as well. You will have to calculate the parameter curve (or SFOR formula) by yourself, as I am not a maths genius :-) or use the method I presented above. Then you will need to modify the animation system so that a TRANSFORM method is correctly used in all other subanimation systems... and this is the reason it is not included in this tutorial. Maybe a future tutorial will explain this. The file 'SimpleTransformEx.obj' may provide some useful information about the TRANSFORM method, and how to apply it in this situation.

Note2:

You'll probably notice that the moon-system has an extra unused level. I have made it this way for easily implementation of more moons in the moon-system level. Also, it's probably better to get used to one way of doing things.

Note3:

If you want to make a complete solar-system of your own, I have included the file 'orbitdata.txt' which contains all neccesary information. The right column have already been scaled to the size I used once, but the FREQ numbers for the PATH and DIRECTION methods will not be correct. (I made my own solar-system in a completely different way than we did above, so please ignore the FREQ values in the right column). In this tutorial we animated the earth and moon using PATH and ROTATION, but for orbits that have a close to zero eccentricity and 'stationary orbit' (like our moon) one could have used DIRECTION method instead of PATH and ROTATION. Note that with these values, bodies will become extremely small, and rendering errors may occur. I.e. Deimos (one of mars' moons) would have measurements of 0.015 x 0.0122 x 0.011 mm (yes millimeters). Zooming in close to this and render, you would notice a whole bunch of jagged egdes due to the accuracy Real3D provides.

Note4:

A very nice way to animate the solar-system as a whole, is to use PATH methods only (forget all about skeletons, rotations and so forth), and set the 2D-particle flag for all the bodies. Enable 'trails' post effect, and render. This is a very fast way of showing the orbits in the solar-system. One can produce a huge animation within a few hours.

Note5:

I have not been able to find specific information about the solar-system. Therefore there might be things that are not even correct. As an example; do the orbits have the same orientation (about the rest of the space) even if it is a suborbit (like the moon)? If this was the case, it would be fairly easy to change the way the orbits behave during the animation time.

I had to experiment a lot on which protected flags to set and which to not set, so in case I have forgot some of the flags, I used the 'Custom/Modelling/Dump Objects' function to generate this list, just in case:

-------------------------------------------------------------
                            | Boolean  Invisib  M  Prot  M  L
                            | -------- -------  A  ----  B  I
                            | A  I  P  W  R  C  P  P  P  L  G
                            | N  N  N  F  T  D  P  1  2  U  H
 Objects                    | D  V  T           I        R  T
-------------------------------------------------------------
 solar-system               | .  .  .  .  .  .  .  .  .  .  .
  system-earth              | .  .  .  .  .  .  .  .  .  .  .
   planet-earth             | .  .  .  .  .  .  .  .  .  .  .
    rotating                | .  .  .  .  .  .  .  .  .  .  .
     parts                  | .  .  .  .  .  .  .  .  .  .  .
      ellipsoid             | .  .  .  .  .  .  .  .  .  .  .
      earth-col             | .  .  .  .  .  X  X  .  .  .  .
     ROTATION               | .  .  .  .  .  .  .  .  .  .  .
      line                  | .  .  .  .  X  X  .  .  .  .  .
    radiosity               | .  .  .  .  .  .  .  .  .  .  .
     light_spot             | .  .  .  .  .  .  .  .  .  .  X
     SKELETON               | .  .  .  .  .  .  .  .  .  .  .
      line                  | .  .  .  .  X  X  .  X  .  .  .
       outer                | .  .  .  .  .  .  .  .  .  .  .
        group               | .  .  .  .  .  .  .  .  .  .  .
        PATH                | .  .  .  .  .  .  .  .  .  .  .
         earth-orbit(l)     | .  .  .  .  .  .  .  X  .  .  .
       center               | .  .  .  .  .  .  .  .  .  .  .
        group.1             | .  .  .  .  .  .  .  .  .  .  .
    transp                  | .  .  .  .  .  .  X  .  .  .  .
     transp-map             | .  .  .  .  .  X  X  .  .  .  .
     SKELETON               | .  .  .  .  .  .  .  .  .  .  .
      line                  | .  .  .  .  X  X  .  X  .  .  .
       outer                | .  .  .  .  .  .  .  .  .  .  .
        group               | .  .  .  .  .  .  .  .  .  .  .
        PATH                | .  .  .  .  .  .  .  .  .  .  .
         earth-orbit(l)     | .  .  .  .  .  .  .  X  .  .  .
       center               | .  .  .  .  .  .  .  .  .  .  .
        group.1             | .  .  .  .  .  .  .  .  .  .  .
   system-moon              | .  .  .  .  .  .  .  .  .  .  .
    moon-moon               | .  .  .  .  .  .  .  .  .  .  .
     rotating               | .  .  .  .  .  .  .  .  .  .  .
      parts                 | .  .  .  .  .  .  .  .  .  .  .
       ellipsoid            | .  .  .  .  .  .  .  .  .  .  .
       moon-col             | .  .  .  .  .  X  X  .  .  .  .
      ROTATION              | .  .  .  .  .  .  .  .  .  .  .
       line                 | .  .  .  .  X  X  .  .  .  .  .
     radiosity              | .  .  .  .  .  .  .  .  .  .  .
      light_spot            | .  .  .  .  .  .  .  .  .  .  X
      SKELETON              | .  .  .  .  .  .  .  .  .  .  .
       line                 | .  .  .  .  X  X  .  X  .  .  .
        outer               | .  .  .  .  .  .  .  .  .  .  .
         group              | .  .  .  .  .  .  .  .  .  .  .
         PATH               | .  .  .  .  .  .  .  X  .  .  .
          moon-orbit(l)     | .  .  .  .  .  .  .  X  .  .  .
        center              | .  .  .  .  .  .  .  X  .  .  .
         group.1            | .  .  .  .  .  .  .  .  .  .  .
        PATH                | .  .  .  .  .  .  .  .  .  .  .
         earth-orbit        | .  .  .  .  X  X  .  X  .  .  .
     transp                 | .  .  .  .  .  .  X  .  .  .  .
      transp-map            | .  .  .  .  .  X  X  .  .  .  .
      SKELETON              | .  .  .  .  .  .  .  .  .  .  .
       line                 | .  .  .  .  X  X  .  X  .  .  .
        outer               | .  .  .  .  .  .  .  .  .  .  .
         group              | .  .  .  .  .  .  .  .  .  .  .
         PATH               | .  .  .  .  .  .  .  X  .  .  .
          moon-orbit(l)     | .  .  .  .  .  .  .  X  .  .  .
        center              | .  .  .  .  .  .  .  X  .  .  .
         group.1            | .  .  .  .  .  .  .  .  .  .  .
        PATH                | .  .  .  .  .  .  .  .  .  .  .
         earth-orbit        | .  .  .  .  X  X  .  X  .  .  .
     PATH                   | .  .  .  .  .  .  .  .  .  .  .
      moon-orbit            | .  .  .  .  X  X  .  .  .  .  .
   PATH                     | .  .  .  .  .  .  .  .  .  .  .
    earth-orbit             | .  .  .  .  X  X  .  .  .  .  .

Lights and Rendering:
These are the setting I used for producing good pictures:
Normal Rendering mode
Ambient 0,0,0
Background 0,4,14
Brightness 20
Overlight 0
Antialiasing 4
Lightsamples 4
Supersample On
AutoExp Off
Rest as default

Earth radiosity spotlight:
Local radius 1.3
Brightness 5
Spot fade 20%
Spot angle 178
Light color 128,130,155
Earth sphere color 255,255,255
Material was replaced with a bigger texture map.

Moon radiosity spotlight:
Local radius 1.0
Brightness 8
Spot fade 20%
Spot angle 178
Light color 89,80,76
Moon sphere color 98,91,83

To simulate a sun, I have two lightplanes perpendicular to each other in the center:
Size 0.4 x 0.4 m
No fading
Brightness 15
Light color 255,252,242

Material settings:
moon-col(T):
Color and Shadow Map On
High level texture
Tile x = -1
Grade x and y
Scope Angle a=-1.1 b=0
Effect = 100

moon-bmp(T):
Color, Bump and Shadow Map On
High level texture
Tile x = -1
Grade x and y
Bump height = 3
Scope Angle a=-1.1 b=0
Effect = 65

Earth-col(T):
Color map On
High level texture
Tile x = -1
Grade x and y
Scope Angle a=-1.1 b=0
Effect = 100

Helpdesk

Real 3D

Main area