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Pop-up | Vertical Shift |
Tide data is used to generate final depths relative to tide datum by subtracting the tide from the sounding depth. This correction provides a more accurate depth value for the surface. When available, tide correction should be applied to all surfaces before using them to create charts.
You can select to load observations from one station or many tide stations. The single station option (Single tide station observations) would be used if your surface falls entirely within a single tide zone. The multiple stations option (Multiple tide station observations) is used if your surface spans multiple tide zones.
Tide zones are closed polygons with tide, time and range corrections for a primary station, plus up to three backup secondary tide stations. |
Observations are loaded from a tide file (.tid) or from a zone definition file (.zdf).
• Tide files contain observations from a single tide station. Applying this file will apply tide observations for the surface for the specified time period. Tide files can be created or edited in a text editor.
• Zone definition files contain data that defines tide zones. Applying this file tells the application where the zones are and in turn, which observations to apply for your surface. Zone definition files are in ASCII format and can be edited in a text editor.
See Tide File Formats for full descriptions of these files.
Procedure
1. Select a surface root layer in the Layers window.
2. Select the Vertical Shift command.
The Vertical Shift Surface dialog box is displayed.
In this dialog box, you define the attribute layers you want shifted and the amount by which to shift them. The resulting surface will contain all of the same layers as the source surface, but only those selected for shift will have their values shifted.
Any layer with a Z value can be shifted.
If the source surface contains a computed layer, that layer will lose its dynamic status and will no longer be affected by changes to the primary elevation layer. |
3. To select a layer, click the layer name in the Available list, then click the Add (right-arrow) button to move it into the Selected list.
4. [Optional] Repeat step 3 for each layer you want to add.
5. [Optional] You can also remove layers from the Selected list by clicking the layer name in the list, then clicking the Remove (left-arrow) button to return the layer to the Available list.
The primary elevation layer is required and cannot be removed from the Selected list. |
6. To apply tide correction, select a tide station observations option.
7. Click the Input file Browse (...) button and select an available file for the selected shift type.
8. Click Open.
The selected file is displayed in the Input file field.
When applying tide correction, you need to specify the date and time of the data to apply. Tide values for a particular area differ depending on the time of year and the time of day. This information is contained in layers in the surface.
9. Using the drop-down lists, identify the layers that contain the Date and Time values.
You have the option of selecting the vertical reference system that will appear in the CSAR metadata for the resulting surface created for the shift. The options available in the list are controlled by the Vertical Reference System database. This list can be edited using the Reference System Editor tool. For more information, see Vertical Reference System.
10. Select a Vertical Datum option from the list.
11. To choose the name and location of the resulting surface, click the Output surface Browse (...) button.
A Save As dialog box is displayed.
12. Select a path and type a name for the shifted surface, then click Save.
13. To finish, click OK.
A new surface is created and displayed in the Layers window. The attributes and properties from the source surface are carried over to the shifted surface. Additional properties are also populated under the Sources group.
• Operation: This property identifies the tool that was used to create the surface. For a shift, it will read “VerticalShift”.
• Vertical Coordinate System: The vertical coordinate system that was used to create the shifted surface.
• Shift Method: This property identifies the type of shift that was applied to the surface.
• Shift File: This property differs depending on the type of shift applied. For a tide shift, it identifies the file of depth values that was used to shift the surface.
• Date/Time Attribute: These properties identify the layers from which date and time values were obtained. These properties are only present for a surface with tide data applied.
• Original Depth Update: This property states whether or not the original depth value of any designated soundings was also updated by the shift. This property is only present if the source surface contained designated soundings.
• Source: This property identifies the name and location of the source surface.
The Z values in the selected layers should be shifted according to the selected method. To confirm that the shift was successful, compare the data in the new surface to the data in the original surface, referencing the adjustments in the tide file. The elevations should have been adjusted according to the data.