Tute M01 Inspect Zpts SAGA: Difference between revisions
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Created page with '<ol> =Introduction= In this page we look at the process on assigning elevations to the TUFLOW Zpts that define the elevations in the model using SAGA GIS. Ensure that SAGA is ope...' |
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[[File:Tute M01 Saga Zpts All2.png|frame|none|400px|All Zpts in SAGA GIS, with attributes selected]]
As can be seen the elevation for all zpts is a nuyll value of 99,999. The next step is to assign values based on the DEM.<br>
<li>Navigate to the ''Modules'' tab in the ''Workspace Window'', expand the ''Shapes - Grid'' entry and right click on the ''Add Grid Values to Points'' and select ''Execute''.</li>
[[File:Tute M01 Saga Modules Shapes Grid.png|frame|none|Shape-Grid Module: Add Grid Values to Points]]
<li></li>In the ''Add Grid Values to Points'' dialogue, set:
* Points to '''2d_zpt_M01_5m_003_P'''
* Result to '''2d_zpt_M01_5m_003_P'''
* Grids to '''DEM_M01'''
Select ''Okay''. See the image below.</li>
[[File:Tute M01 Saga Add Grid Val to Pts.png|frame|none|Add Grid Values to Points Dialogue]]
In the map window, if you select a point with the ''Action'' cursor and navigate to the ''Attributes'' tab in the ''Objects Properties'' window, a new data attribute '''DEM_M01'''. This field should have an elevation assigned:<br>
[[File:Tute M01 Saga Zpt Fields2.png|frame|none|Attributes after DEM value added to points]]
<br>
If you select a Zpt outside the DEM area the value that has been assigned to this attribute is -99,999. We will remove any Zpts that have this elevation.
<li>In the ''Modules'' option select ''Shapes - Tools >> Select by Attributes... (Numerical Expression)</li>
<li> Set the following:
* Shapes to '''2d_zpt_M01_5m_003_P'''
* Attribute to DEM_M01
* Expression to "eq(a,-99999)" (without the quotes)
Select ''Okay''.
[[File:Tute M01 Saga Select By Attribute.png|frame|none|Select by Attribute]]
<li> Navigate to the ''Data'' tab in the ''Workspace'' window. The Zpts outside of the DEM should be highlighted. To delete these, right click on the '''2d_zpt_M01_5m_003_P''' item and select ''Edit >> Delete Selected Shapes''. The map window should look like the below:</li>
[[File:Tute M01 Saga Zpt NullRemoved.png|frame|none|Map View with null Zpts Removed]]
TUFLOW requires the elevation data to be in the fourth column and the inspection has added a fifth column with the DEM values. There are two ways of overcoming this:
* Updating the fourth (elevation) attribute column to have the values of the newly created (RASTERVALU) attribute.
* Remove the elevation column, so that the RASTERVALU column becomes the fourth column.
We will demonstrate the second option, the first option will results in the same data being stored twice in the shapefile, which will mean bigger file sizes.<br>
<li>In the ''Data'' tab, right-click on the '''2d_zpt_M01_5m_003_P''' item and select ''Attributes >> Show''. This should bring up a tabular view of the data:</li>
[[File:Tute M01 Saga Zpt Attributes1.png|frame|none|2d_zpt_M01_5m_003 Attributes]]
<li>Select the ''Delete Field'' icon (highlighted above)</li>
<li>In the dialogue, check the elevation check box and select ''Okay''</li>
[[File:Tute M01 Saga Zpt DeleteField.png|frame|none|Delete Fields Dialogue]]
<br>
By deleting the Elevation field we have promoted the DEM_M01 field to the fourth position and will be used by TUFLOW. In the map window, if you select a point with the ''Action'' cursor and navigate to the ''Attributes'' tab in the ''Objects Properties'' window, the output should look like this:<br>
[[File:Tute M01 Saga Zpt Fields3.png|Attributes After Removal of Elevation Field]]
<li>In the ''Data'' tab, right click on the '''2d_zpt_M01_5m_003_P''' item and select ''Save''</li>
We have now updated the GIS layer, the next step is to modify the TUFLOW geometry control file to read the new shapefile.<br>
<li>Save the current TGC file as '''M01_5m_003.tgc'''. Comment out or delete the Write MI and Stop lines entered previously (these are no longer needed).</li>
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