How to Start
- Select Soundings... option from Dynamic Surface menu of Main Menu bar
What it Does
This dialog runs the soundings selection operation on the currently selected surface.
After selecting a dynamic surface from the layers window utilize this dialog for various sounding selection actions. If you have selected a rectangular area from the main window you can restrict the actions to the selected area by changing the scope from Entire Surface to Selection.
Selecting Soundings to Mark Suspect
The suspect soundings selection filter assists the user in identifying soundings that may be incorrect. Clicking the Run button in the Suspect Sounding Clearing Filter section will display the Suspect Filter Options dialog. The filter will select all soundings with depths that are more than a certain threshold away from the average depth in a cell. Enter a threshold in the Depth Threshold Difference text field and click the Filter button
Selecting Soundings to Mark Plotted
The NAVO sounding selection algorithm will select and mark soundings in a dynamic surface with the plotted flag when it selection criterion is set. Clicking the Run... button opens another dialog that lets you set parameters for the selection process as shown below. Once you have selected desired parameters the filter will run and soundings that pass the selection criterion will have their plotted flag set.
Normally the chart scale is specified to determine the default distance between selected soundings that are entered in the Chart Scale text field. For example a value of 20000 implies a chart scale of 1:20000. This gives the default minimum distance between soundings and is based on assuming 5mm text for the resulting chart. You can directly enter the minimum distance, overriding the suggested default for the given chart scale, by typing a new value in the Minimum Distance text field. The Selection Factor that defaults to two is used in algorithm and generally should be left alone. A smaller number improves the quality of the selection but increases running time (the default has been found to be a good balance). The Cell Size is read from the Dynamic Surface and is fixed. The Parameter Status field shows the criterion for running the algorithm. You cannot select soundings if you select an unreasonable chart scale for the cell size of the dynamic surface. The dialog box will display a message just below the parameter status to indicate if the selected parameters are acceptable or not. If they are not you must increase the chart scale (or minimum distance).
Feature Selection Filters
A dropdown menu in this section currently provides two filter algorithms which can be used to select and mark soundings by setting their feature flag. These are the Feature Filter and the Shoalest algorithm described below. The Feature Table... button will bring up a spreadsheet to of soundings with the filter flag set in the selection scope.
Feature Filter Algorithm
When selected and you click Run..., another dialog will appear to set the selection interval, the z-range minimum, and the z-range maximum. Specify the minimum distance apart of shoals in the horizontal plane (Selection Interval), and specify the depth range for consideration in the Z Range Minimum and Z Range Maximum text fields. Click the Filter button to begin the algorithm.
The actual algorithm is a two-step process. In the first step, it searches through all the data based on the defined cell size and finds the shallowest sounding that is not flagged as deleted and is within the selected depth range. In addition, the entry of the minimum and maximum values allows the user to restrict the process to only those soundings within the selected depth range. The second step prunes the list of selected shoal soundings based on the range interval entered. In this step, the selected soundings are first sorted in descending order. The shallowest is selected and then any sounding that lies within the entered range is deleted. The next shallowest sounding is selected and any soundings that lie within the entered range to it are deleted and so on.
When selected and you click Run... this algorithm will mark the shoallest sounding in each cell of the dynamic surface.
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