The tool 'Auto update cross sections' may be used to update elevation data of existing cross sections using a DEM. Additionally, the tool may update only a part of the cross sections: this may be useful when a recent DEM is available but only covers floodplains, and in this case the DEM can be used to update the cross sections elevations in the floodplains while keeping the elevations in the riverbed unchanged.
Two options are available to control the extent of the cross sections to be updated:
· Update whole cross sections: This updates the elevation data all along the cross sections.
· Update parts of cross sections: This updates the elevation data only along parts of the cross sections. When applying this option, it is possible to select the two makers defining the part of the cross section which is NOT updated.
When applying the option 'Update parts of cross sections', and additional option 'Update levels for these markers' is also available. When it's checked, levels of the selected markers are updated, whereas levels of the selected markers are unchanged when the option is unchecked. As an example, it is possible to update the elevation data only in the floodplain by use of markers 4 and 5, which may be located on the banks. If banks levels are obtained from a survey which is assumed to be more accurate that the DEM used to update the floodplain, then the option should remain unchecked in order not to update the bank levels. On the opposite, if the new DEM is assumed to be more accurate than original data describing the banks, the option should be checked to update the bank levels as well.
Regardless of the selected option, the tool updates elevation data (Z-values in the raw data table) but keeps the following data unchanged:
· Coordinates
· S-values of the start and end points of the cross section
· S-values of the markers.
The update is controlled by the options specified in the 'Digital Elevation Model (DEM)' page, which control e.g. the spacing between points extracted from the DEM. Therefore a different number of raw data points may be obtained in the updated cross sections, compared to the original cross sections. This may be useful to best benefit from a new DEM with a higher resolution than the data used to create the original cross sections.
Options selected here control on which branches or parts of branches the cross sections should be updated. Four options are available:
· All cross sections: All cross sections in the model will be updated.
· Selected cross sections: Only the selected cross sections will be updated.
· Cross sections from selected branches: Only the cross sections on the selected branches will be updated.
· Cross sections from table of reaches: The locations of cross sections to be updated are specified in a table, offering flexible options to control the branches to be included, and also the range of chainages for each branch, where cross sections are updated. Cross sections are updated only between the specified lowest and highest chainages, and if the box is checked in the 'Include' column.
When the option 'Cross sections from table of reaches ' is used, the following buttons are available above the table:
· 'Import all': Imports all branches in the table, i.e. it creates one row for each branch in the model. Each branch is given its default lowest and highest chainages.
· ‘Import from file': Imports the 'Branch name', 'Lowest chainage' and 'Highest chainage' from a text file. The file format is: three columns with lowest chainage, highest chainage and branch name (in this order), with one separate line for each row of the table. Columns must be space-separated or tab-separated.
· 'Include all': Checks all boxes in the 'Include' column of the table.
· ‘Exclude all': Unchecks all boxes in the 'Include' column of the table.
· Update: updates cross sections following the specifications in the dialogue window.
· Save log: Saves the messages issued during the generation to a text file.
· Clear log: Clears the log-messages in the text box above the buttons.
· Close: Closes the tool.