Whenever a three dimensional dataset has been selected from an HDF file, the user will have to specify the orientation of the two dimensional slab to extract ( Section 3.4: The Orientation Menu), and a value or array index along that dimension from which to extract data .
By default, a user may select a new level either by index or by value (section 3.5.1). However, if no dimension information is stored with the current dataset, then the user will only be allowed to select by index only (section 3.5.2).
The following control panel will be displayed when the Change Level option has been selected from the main menu.
Figure 3.5a: Control panel for selecting a new level by index or value
Orientation: Label specifying orientation of the slab. (Section 3.4:The Orientation Menu).
Name: Label specifying character string of the name of the fixed dimension from
which the data will be selected.
Units: Label specifying character string of the units of the dimension from which
data will be selected.
Min[Index]: Label displaying minimum array index that user can select.
Max[Index]:Label displaying maximum array index that the user can select .
Min[Value]:Label displaying minimum array value which will be accepted.
Max[Value]:Label displaying maximum array value which will be accepted.
Index/Value: Tick boxes which specify the mode by which the user will select a new level. The default setting is by index. To change the mode, click in one of the two tick boxes using the left hand mouse button. The mode selected will active/inactivate the corresponding text input objects. If the Index option is set, the Index[1] text input object will be activated, so that it can recieve user information. If the Value tick box has been selected, the Value[1] text input object will be activated and the Index[1] text input object inactivated.
Index[1]: Text Input field which displays the currently select array index along which data will be extracted. Array index must be in the range specified by the Min[Index] and Max[Index] labels.
Value[1]: Text input field which displays the currently selected array value along which to extract data. Value must be in the range specified by the Min[Value] and Max[Value] labels.
Difference Queries.
For a difference query , the user must specify the second level . A second line will appear on the control panel, by which the user can enter the level or value for the second variable.
Figure 3.5b: Change Level Panel for a difference query
Text Fields:
There are two ways in which the values in the text input fields can be updated:
a) By entering new text via the keyboard. To accept text via the keyboard the text input field must be enabled.
b) By using the arrow keys to increment or decrement the index/value text fields depending on the mode selected.
Using the Keyboard:
Depending on which on the text fields are active , click on the text input line to active the prompt. Using the Delete/Backspace key, delete the existing entry and then type in the new index or value you wish to extract for. Press the Return Key. This will switch the prompt off and check the values you have entered. If selecting a slab of data by index, the new level entered will be checked to see if it is valid. If is not valid, then an error message will be displayed on the screen below the Accept and Cancel buttons. Otherwise, the program will retrieve the value along the dimension extracting data from and update the Value[] text field. If extracting data by value, the program will find the nearest matching value in the scales associated with the dimension data is being extracted from and update the Value[] text field with this value and also update the Index[] text field with the index to which this value corresponds.
Using the arrow keys:
The user may also use the arrow keys to increment and decrement the values in the text input fields. To increment the current index or value simple click once using the left hand mouse button on the Up arrow key. To decrement the current value, click once on the Down arrow key using the left hand mouse button. After each click of an arrow key, the index or value will be checked to see if it withing the current limits. If that index or value is outside of the valid range and error message will be displayed and the text fields remain unchanged.
Accept: To accept the current values displayed on the control panel, click once on the button using the left hand mouse button. Depending on the mode selected i.e either by index or by value, the program will check that the prompt for the corresponding text input field is switched off. If the prompt is still displayed, this means that the last value entered as not being processed. The program will now process the text has specified above. If the values are out of range an error dialog box will be displayed on the screen informing the user, that the request is not valid. If the level and the corresponding value are valid, then a new message box will appear on the screen, listing the levels and their corresponding values requested previously.
Figure 3.5c: Accepting levels and values specified by control panel.
The Level[1] displays the level entered and the Value[1] label displays its corresponding array value followed by the units along the dimension specified by the orientation. To accept the results, place the cursor over the Accept button and click once using the left hand mouse button. The new level will now be extracted and the new image displayed on the screen.
Cancel: This option will terminate the current selection of a new level and the data will not be changed.
Section 3.5.2: Selection by Index only.
If no dimension information is stored with the dataset, the user will only be able to change a level by selecting a new array index. The control panel for selecting a new level by index only will be displayed on the screen.
Figure 3.5d: Selection of a new level by Index only.
Orientation:Specifies orientation of current selected slab.
Min[Index]: Minimum valid array index accepted.
Max[Index]:Maximum valid array index accepted.
Index[1]: Text Input Field for array index. When the control panel is opened , the text field will display the level of the current 2-D slab displayed on the screen. ( Default setting is 0 ). To change the value using the keyboard, click on the text input line using the left hand mouse button. Using the Delete or Backspace key, delete the current entry and retype a new value. Press the Return key, to check if this is a valid entry. An error message will appear on the control panel if this is an invalid entry. To change the value using the arrow keys, click once on the Up or Down arrow key once to increment or decrement the index by one. An error message will again be displayed if an invalid entry is made.
Accept: Accepts the index value in the text input field. If the prompt is shown on the text input line, the last entry has not been processed correctly. A check will be made to ensure that this is a valid entry. If it is not a valid entry then the control panel will be closed and an error dialog box displayed on the screen. The current level will not be changed. If the level entered is valid, the Accept Levels [figure 3.5e] message box will now be displayed so the user can confirm their selection.
Cancel: Cancels any requests made and closes down the control panel, without changing the current level. Terminates the selection of a new level.
Figure 3.5e: Accepting Levels by Index Only
Accept:Confirms the selection of the new level. The data will now be extracted and the limits window will now be displayed (section 4.2: Specifying Data Min/Max ).
Cancel: Cancels selection. Level remains unchanged, and the control panel is closed down.
Section 3.5.3:Resetting Image Parameters.
If an image is already displayed on the screen and new data has been selected, or the level has changed, then if the two datasets are of the same size and of the same orientation, the user has the option of maintaining the same view and the same data limits as the previous image. These can be set using the following control panel:
Figure 3.5f: Reset Image Parameters.
By default, both the view and the limits of the data displayed will reset, whenever there has been a change in the data. To prevent either of these changing, click once on the selected tick box. When no tick appears in a box, the corresponding action will not take place. When setting the limits option, the user must be careful since the two types of data plotted may not have the same units. If the user decides not to reset the limits of the image data, the limits of the last image displayed will be used.
Please note: If the type of data has changed the user is advised to reset the limits option.