7.2 - Data Processing for OpenDX

Similar to Maple, the data which OpenDX reads in must be in the appropriate format for the software to understand. But because the dataset is stored in Excel format, it can easily be converted into plain ASCII text file (.txt) format which OpenDX can understand.

Since OpenDX can only plot scattered data in Cartesian coordinates, a transformation of the dataset from cylindrical coordinates is also necessary. There are two methods to achieve this. The first method is to write a macro in OpenDX visual program which uses the Mark, Compute and Unmark modules to do the conversion. The second method is to convert the data in Excel and then later input into OpenDX. Since OpenDX is not intentionally used as a data manipulation package as compared to Excel, the second method was chosen.

The magnitude of the angular velocity was scaled 1000 times. This was done or else the value of the angular velocity w will be too small to be seen on the graph (see figure 7.2.1). Also in every fourth column of the dataset, cardinal numbers (e.g. 1,2,3... ) were inserted. The number was assigned to differentiate the particles in the cluster. The data was formatted so that they are all in scientific form with accuracy of up to 4 significant figures. The data was then saved in tab delimited text (.txt) format.

Figure 7.2.1 - Cardinal number was inserted into the fourth column to index the different particles in a cluster. So the dataset is consisted of position and particle index number.

Text file incompatibility between Unix (which my OpenDX runs on) and DOS (which my Excel runs on) system was a problem after the dataset was saved as text format. Apparently this is a common problem and it arises because Unix and DOS system interprets new line feed differently. Unix interprets all new line feed from DOS files as the character <cr> (or carriage return). This creates a data reading error for OpenDX. To overcome this problem, a program called Treptos 1.0 was used to convert the DOS file into Unix files where all the carriage return has been removed.