# The Control bar

• Overview: The Control bar both changes and displays the current axis, subsample rate and zoom factor.
• Axis: The axis symbol shows the current orientation of the axis. Clicking the axis symbol rotates the axis. Each left click rotates the axis counter-clockwise 90 degrees. Each right click rotates the axis clockwise 90 degrees.
• Subsample: The subsample factor determines the fraction of data points in the file that are displayed. The subsample factor operates differently depending on whether the data points are on a uniform grid or are on a non-uniform grid. For a uniform grid every {subsample} data point is displayed. For example, if the subsample factor is one, every data points is displayed; if it is changed to ten, every tenth data point is displayed. This results in a reduction, by a factor of one hundred, in the total displayed data points. For a non-uniform grid the program constructs a uniform grid which it uses as a mask on top of the non-uniform grid. The details of how the program constructs this uniform grid is given in the input file format section of the docs. The program finds, for each square of the uniform grid, the non-uniform grid data point that is closest to the center of each square in the uniform grid. It then displays for each square of the uniform grid that closest data point- but at the data point's location on the non-uniform grid. What sample size affects in the case of a non-uniform grid, is the relative coarseness of the uniform grid. A larger sample size will make larger squares on the uniform grid that on average will contain more of the non-uniform grid's data points and will thus result in less vectors being displayed. A smaller sample size will make smaller squares on the uniform grid that will on average contain fewer of the non-uniform grid's data points and will thus result in more vectors being displayed. The numeric value of sample size is the ratio of the size of a grid square in the current uniform grid compared to the size of a grid square in the original uniform grid i.e .5 means grid squares half the original size resulting in a grid with four times as many points. Note also that the arrow size is adjusted so that the arrow will fit inside the uniform grid so that adjusting the subsample factor will also adjust the overall arrow size. In addition note that a subsample factor of zero simply displays every vector in the data.
• Changing the Subsample factor: Two techniques using the control bar can be used to change the subsample factor. The first technique is to move the top scale bar until the subsample factor is the desired value. The second technique is to simply left-click on the number to the right of subsample:. The desired subsample factor can then be typed in. The subsample factor can also be changed using the keyboard.
• Arrow mag: Arrow mag allows the user to change the arrow display size in mmDisp. Increasing the arrow magnitude value will draw longer arrows on the display. Decreasing the arrow magnitude value will draw shorter arrows on the display.
• ZOOM: The zoom controls the magnification of the vector display. Assuming no other changes, increasing the zoom factor results in a smaller region of data displayed in the same size window with a corresponding increase in arrow size. However the size of the arrow, as discussed below, depends also on the subsample rate and the size of the frame. The zoom factor is the number of pixels in the frame divided by the number of arrows in the frame assuming the subsample rate is one. When the subsample rate is increased from one, the number of arrows is decreased and the number of pixels available to each arrow is increased causing an increase in the arrow's size. Thus the subsample rate also effects the size of the arrows but in a way independent of the zoom factor. The subsample rate corresponds to the resolution of the display while the zoom factor corresponds to the closeness to the display.
• Changing the Zoom level: Two techniques using the control bar, one technique using the keyboard, and one technique that works by outlining an area in the display window, can be used to change the zoom level. The first technique is to move the bottom scale bar until the zoom factor is the desired value. The second technique is to simply left-click on the number to the right of Zoom:. The desired zoom value can then be typed in. A menu command, Fill Display , can also change the zoom level.
• Turning Off: The control bar may be turned off by toggling the control bar option off under the option menu.

Go to the top