Firstly I'd like to mention some initial problems I have come across and what I have done to fix them, and changes I have had to make to the UML plan.
In the CreatePlanet class, i have added longitudeAscendingNode and longitudePerihelion as private instance variables (doubles). This was an oversight, as these values are required in the calculations for x1, y1 and z1. I have also removed periodOfOrbit as a variable in CreatePlanet, and moved it to the OrbitalCalculations class. I found it was easier to calculate the period of orbit using the semi-major axis, instead of hard code in a value for each planet.
The bulk of changes has occured in the OrbitalCalculations class. Firstly, meanAnomaly has been added as a private instance variable. I'm not sure why I left this out, but the variable is required to calculate the mean anomaly in the drawOrbit method. Secondly, I found I had neglected to consider the need of parameters in the majority of the methods. This was a mistake as of course most of the calculations utilise data which will, in the end, be taken from the created planets. These changes are as follows:
As you can see from the image, I have also renamed the vector class to Vector3D. I was a bit worried about vector being a reserved C++ word, so changed it to be on the safe side. Another change is to make the drawOrbit method Vector3D, instead of void. This simply means that the method returns the coordinates in vector form, instead of having another method to do this.
One of the major issues I knew I would have is calculating the eccentric anomaly. I tried out a few iteration methods that didn't work, but managed to find C# iteration code on this website: http://www.jgiesen.de/kepler/kepler.html. I adapated this code into C++, and tested it to give the same results as the calculator on that website. A screenshot of this method is below:
The final drawOrbit method utilises all the previous methods in the class to calculate the final x,y,z coordinates, here is a screenshot of this method:
I have also included test printing in this method, which will print the various stages to the console when the method is called in DrawSolarSystem. I had an issue with printf, the printing mechanism I have previously used in C++, and so decided to use cout as my test printing method throughout the program.
I had one final major oversight at this stage, which became apparent when I went to create the planet and test the drawOrbit method in DrawSolarSystem. The mean anomaly calculation requires a current time and a time since the planet was last at the perihelion point to be defined - what format was that in? I hadn't previously considered this fully. With some research, I discovered that astronomers use the Julian dating system (defintion), and thus my program would have to have some system of converting standard (Gregorian) dates into Julian dates. What I did was to add another class, called DateTime. In this class a date with a year, month and day can be defined, then a method called to convert it into a Julian date. It also has a method to convert a Julian date back into a Gregorian date, should it be necessary. The calculations for these methods were adapted from the following website: http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/julian-date-form. I also used this website which calculates Julian dates to confirm that the method works correcetly. A screenshot of the class is below:
Now i was able to create a planet in the InitGL class of DrawSolarSytem, and call the drawOrbit method of OrbitalCalculations in order to check the test prints. Here are some screenshots of the method, and the resultant console print out:
As you can see, data is given out for each calculation, so it's definately doing something!
Now onto the unresolved problems. As of yet, I haven't been able to find any data to verify and compare the majority of my answers with, aside from the Julian date and obvious ones like period of orbit.
In addition, you may have noticed commented out code to test Mercury as well as the Earth. I've searched for quite some time today trying to find dates for when Mercury was at it's perihelion point, but have so far been unable to find any data. This was easily sourcable data for the Earth, but appears much harder to find for other planets, and is something I will be consulting my supervisor about.
That's pretty much it for this week, some useful links I've found and used this week to follow.
Useful Links:
Perihelion dates for the Earth - dates for when the Earth was/will be at it's perihelion point. Would be lovely to have a similar table for other planets!
http://www.met.reading.ac.uk/~ross/Documents/OrbitNotes.pdf - contains slightly different orbital elements data than the JPL source I have been using. Something to discuss with Rob?
http://www.devmaster.net/forums/showthread.php?t=5059 - How to load 3Ds max objects into OpenGL. Could be useful if my current method fails.
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