Emilie Nielsen at 00:15, 23 September 2024

2024-09-23T00:15:31Z

← Older revision		Revision as of 10:15, 23 September 2024
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	[[File:Tute M01 QGIS Zpts2.png \| frame \| none]]		[[File:Tute M01 QGIS Zpts2.png \| frame \| none]]
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	<li> Select OK to begin the inspection, the progress should be shown in the "Status" section of the dialogue as below. This inspection may take a while ~~(now might be a good time to read Section 4.4 of the 2010 TUFLOW manual)~~.</li>		<li> Select OK to begin the inspection, the progress should be shown in the "Status" section of the dialogue as below. This inspection may take a while.</li>
	[[File:Tute M01 QGIS Zpts3.png \| frame \| none]].		[[File:Tute M01 QGIS Zpts3.png \| frame \| none]].
	<li>Once the inspection has been completed, we need to remove any elevation point (Zpts) where the points are outside the extent of the DEM. During the inspection process these points were given the DEM_M01 value of Null or 0.<br>		<li>Once the inspection has been completed, we need to remove any elevation point (Zpts) where the points are outside the extent of the DEM. During the inspection process these points were given the DEM_M01 value of Null or 0.<br>

ElizaCollison: Created page with "
=Introduction= In this page we look at the process on assigning elevations to the TUFLOW Zpts that define the elevations in the model using QGIS. In this process we will..."

2023-01-09T01:58:57Z

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 QGIS. In this process we will..."

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<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 QGIS. In this process we will open a shapefile containing all of the Zpts and then inspect the elevations from a DEM. 
The process is similar to the process in QGIS, MapInfo and ArcGIS. However, this process is significantly slower in QGIS, taking approximately 30 minutes. Therefore, it is recommended that [[Tute_M01_Inspect_Zpts_ASC_Archive|direct input of DEM]] is used instead. Direct input of the DEM has the following benefits:
* Speed, direct input of the DEM to TUFLOW, is much faster than the process outline below; and
* Flexibility, if the cell size of the TUFLOW model is changed, the process below will need to be repeated, for a direct input of DEM or TIN, this is not necessary.
 
The process of inspecting the Zpts in QGIS is outlined below for completeness.

=Method=
<li>Open QGIS and ensure that the DEM is open, the DEM can be found in the '''Module_Data\DEM\QGIS\''' directory.</li>

<li>Open the blank Zpt layer '''2d_zpt_M01_5m_002_P.shp''', this was written in the '''TUFLOW\Model\gis\''' directory. The Zpts will appear as a mass of points when zoomed to the full extent. The zpts should appear as per the image below.</li>
'''Tip:''' The layer can be added be either using the '''Layer >> Add Vector Layer''' dialogue, using the shortcut keys '''Control + Shift + V''', or by dragging the '''2d_zpt_M01_5m_002_P.shp''' from windows explorer onto the '''Layers''' area of QGIS.

[[File:Tute M01 QGIS Zpts1.png | frame | none]]
 
<li>Ensure that the '''point sampling tool''' plugin is installed. Instructions on installing this can be found on the [[QGIS_Point_Sampling_Plugin |QGIS Point Sampling Tips]] page.</li>
<li>Start the plugin, by selecting '''Plugins >>> Analyses >>> Point Sampling Tool'''.</li>
<li>In the Point Sampling Tool Dialogue:
:* Ensure that the layer containing sampling points is set to '''2d_zpt_M01_5m_002_P'''.
:* Set the output point vector layer to '''\TUFLOW\model\gis\2d_zpt_M01_5m_003_P.shp'''.
:* Select the following layers 2d_zpt_M01_5m_002_P : n, 2d_zpt_M01_5m_002_P : m, 2d_zpt_M01_5m_002_P : type and DEM_M01 : band 1 (the Elevation from the source point is omitted as this contains only null elevations).</li>
The Point Sampling Tool dialogue should appear as below:
[[File:Tute M01 QGIS Zpts2.png | frame | none]]
 
<li> Select OK to begin the inspection, the progress should be shown in the "Status" section of the dialogue as below. This inspection may take a while (now might be a good time to read Section 4.4 of the 2010 TUFLOW manual).</li>
[[File:Tute M01 QGIS Zpts3.png | frame | none]].
<li>Once the inspection has been completed, we need to remove any elevation point (Zpts) where the points are outside the extent of the DEM. During the inspection process these points were given the DEM_M01 value of Null or 0. 
In order to select the points with a DEM_M01 value of zero, right click on the '''2d_zpt_M01_5m_003_P''' entry in the layers table of contents and select '''Open Attribute Table.'''</li>
[[File:Tute M01 QGIS Zpts4.png | frame | none]]
 
<li>In the '''Attribute Table''' dialogue:
* Set the layer to be editable using the toggle editing button which is shaped like a blue pen;
* Type "Null" (without the quotes) into the "Look For" section, at the bottom of the dialogue; and
* Set the field to look for "Null" to be DEM_M01, using the drop down box. 
Once these have been filled out, the dialogue should appear as below, when finished, select search.</li>
[[File:Tute M01 QGIS Zpts5.png | frame | none]]
 
<li>After a few seconds, the "Null" entries should be highlighted, select the '''Delete Selected Features''' (Control + D) option.</li>
<li>You will be prompted to confirm the delete, the items to be deleted will be highlighted. There should be 10,969 features to be deleted. Select '''OK''' to confirm.</li>
[[File:Tute M01 QGIS Zpts6.png | frame | none]]
 
<li>The delete process may take a minute, once completed, select the "Toggle Editing" button to complete the edits. When prompted select, '''Save'''.
[[File:Tute M01 QGIS Zpts7.png | frame | none]]
 
We have now updated the GIS layer, the next step is to modify the TUFLOW geometry control file to read the new shapefile. 
<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>

<li>Add the following lines to the TGC file and save.</li>
<tt>Set Zpts </tt> <tt>== 75</tt> 
<tt>Read RowCol Zpts </tt> <tt>== </tt> <tt>..\model\gis\2d_zpt_M01_5m_003_P.shp</tt> 
== Conclusion ==
The Zpts have been inspected from the DEM, the geometry control file (.tgc) updated to use the inspected Zpts. Please return to the tutorial model module 1 page where the next step is to [[Module1_test_Archive#Define_Preliminary_Active_and_Inactive_Areas_of_the_2D_Domain|define the active areas]].
</ol>

Tute M01 Inspect Zpts QGIS Archive - Revision history

Emilie Nielsen at 00:15, 23 September 2024

ElizaCollison: Created page with " =Introduction= In this page we look at the process on assigning elevations to the TUFLOW Zpts that define the elevations in the model using QGIS. In this process we will..."

ElizaCollison: Created page with "
=Introduction= In this page we look at the process on assigning elevations to the TUFLOW Zpts that define the elevations in the model using QGIS. In this process we will..."