A surface can be shifted by a single value. If you select this option, the value you enter in the Shift value field is used to shift the selected layers. The direction of the shift depends on the current application settings for the Z-axis Convention attribute.
For example, if the elevation is 12 metres below the datum and a shift of (positive) 10 metres is applied:
• if the Z-axis Convention is set to “Down is positive,” the result is 22 metres below the datum.
• if the Z-axis Convention is set to “Up is positive,” the result is 2 metres below the datum.
To apply a vertical shift using a single value:
1. Select a surface root layer in the Layers window.
2. Select the Vertical Shift command.
The Vertical Shift Surface dialog box is displayed.
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. Select Single Shift from the Shift type drop-down list.
7. Type a value greater than zero in the Shift value field.
You have the option of selecting the vertical reference system that will appear in the CSAR metadata for the resulting surface. 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.
8. Select a Vertical Datum option from the drop-down list.
9. To choose the name and location of the resulting surface, click the Output surface Browse (...) button.
A Save As dialog box is displayed.
10. Select a path and type a name for the shifted surface, then click Save.
11. 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 “Vertical Shift”.
• Vertical Coordinate System: The vertical coordinate system that was used to create the shifted surface.
• Additional Attributes: This property identifies the attributes from the source surface that were shifted.
• Shift Method: This property identifies the type of shift that was applied to the surface.
• Shift Value: This property differs depending on the type of shift applied. For a single‑value shift, it identifies the value by which the surface was shifted.
• 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. All elevations should be adjusted by the specified amount.