Chapter 6. A Brief Overview of Data Objects
Prev |  | Next

# Chapter 6. A Brief Overview of Data Objects

There is more to KST than simple plotting and viewing of data. From the data wizard, you have already seen that KST has the ability to create power spectra of data. In fact, KST is also capable of creating other data objects such as histograms, equations, and plugins. A utility called the Data Manager can help you keep track of all the data objects you create.

Start KST with the file `demo.kst`, included in the demo package:

    kst demo.kst

This KST session contains vectors and other data objects created from data in `gyrodata.dat`. The top plot contains the azimuth data, the middle plot contains the pitch data in blue, and the bottom plot shows the power spectrum of the pitch data in blue. Let us first examine the plots more closely. Tie the top two plots together using the techniques you learned in the previous section. Then hold down Ctrl to enter X Mouse Zoom mode. Now zoom in on a small region of the top plot (say from 50000 to 53000), to cause both tied plots to zoom. You will notice that the blue pitch curve is negatively correlated with the red azimuth curve. This is because the pitch gyro was slightly rotated relative to the azimuth axis (by -0.69 degrees). The true pitch `p'` is:

where `p` is the original pitch, is the rotation of the pitch gyro relative to the azimuth axis, and `a` is the azimuth gyro. `p'` is plotted as the black curve in the middle plot. The power spectrum of `p'` is the black curve in the bottom plot.

Now let us take a look at how the three plots were created. To display the Data Manager, select Data Manager... from the Data menu, or click the toolbar button:

The Data Manager contains the definitive list of data objects in the current KST session. It also allows you edit or create new data objects. As you can see, there are three curves (each created from a pair of vectors), one equation, two power spectra, and four data vectors listed. Right-click on C2-GY_PITCH and select W1-P1 from the Remove From Plot submenu. This removes the curve from plot P1 in window W1. Also remove PSD2-V3-GY_PITCH from plot P3 in window W1 using the same procedure. Now only the corrected curves should be displayed in the plots:

To see how the corrected pitch gyro was created, highlight C4-cleaned_pitch and click the Edit button. The Edit Equation dialog should be displayed:

Note that the equation used to calculate `p'` was entered in the Equation text box (an approximation of 1 was used for `cos(-0.69)`). Feel free to experiment with the settings in this dialog. Click OK (to save any changes made) or Cancel when you are done.

Note that all data objects have a number listed under the # Used column. This number indicates the number of times the data object is either used by other data objects or by plots. Since we removed a curve and a power spectrum, at least two data objects should have 0 listed under this column. Click Purge to permanently remove all unused data objects.

Click Close to close the Data Manager. You can exit KST now if you wish.

Prev |  | Next
Chapter 5. The Basics of Plot Manipulation | Home | Chapter 7. A Look at Plugins and Events