[Create grid shape solving Poisson equation]

Create grids by solving poisson equation to region which is defined by [Center line], [Left bank line], and [Right bank line].

Grids generated by this algorithm consists of cells that are similar to square, so it helps solvers do stable simulations.

Figure 249 shows an example of a grid created by this algorithm.

../../_images/poisson_example_grid.png

Figure 249 Example of a grid created by solving Poisson equation

When this algorithm is selected, if a river survey data is imported, The dialog in Figure 250 is shown.

When you specify the number of Control Cross Sections and click on [OK] button, center line is defined by using the river center lines of river survey data, as shown in Figure 251.

../../_images/poisson_select_control_xsec_dialog.png

Figure 250 [Specify the Number of Control Cross Sections] dialog

../../_images/poisson_centerline_example.png

Figure 251 Example of center line

Next, please generate left bank line and right bank line. Select [Build Left bank and Right bank lines] from menu. [Build Bank Lines] dialog (Figure 252) will be shown. When you input the distance on the dialog and click on [OK], Left bank line and Right bank line are generated, and shown like in Figure 253.

../../_images/poisson_banks_dialog.png

Figure 252 [Build Bank Lines] dialog

../../_images/poisson_banks_example.png

Figure 253 Example of generated Left bank line and Right bank line

Center line, Left bank line, Right bank line can be imported from Shape files or CSV files.

At last, select [Create Grid] from menu. [Grid Creation] dialog (Figure 254) will be shown.

When you input the number of division, and Maximum number of iteration on the dialog, and click on [OK], the grid is generated.

An example of generated grid is shown in Figure 255.

../../_images/poisson_gridgeneration_dialog.png

Figure 254 [Grid Creation] dialog

../../_images/poisson_grid_example.png

Figure 255 Example of generated grid

Attention

When you specify a small [Max number of iteration] value, Poisson equation will not converge enough.

Attention

When you create grids using this algorithm for strongly curved rivers, it sometimes occurs that grid cells get inverted, like shown in Figure 256. When you get grids like this, please try again with different values of nI and nJ, to change rate between them.

Generally speaking, this kind of problem seldom happens when you input nI and nJ value to make dI and dJ values almost the same.

../../_images/poisson_bad_example.png

Figure 256 Example of grids with inverted cells

[Build Left bank and Right bank lines]

Description: Generate Left bank and Right bank lines.

Dialog in Figure 252 is shown, so specify the distance values and click on [OK].

Figure 253 shows an example of generated [Left Bank Line] and [Right Bank Line].

You can modify the lines by dragging the vertices.

[Add Vertex] (A)

Description: Add vertices to lines

When you move the mouse cursor to hover on [Center line], [Left Bank Line], or [Right Bank Line] after selecting this menu, The mouse cursor changes to the shape in Figure 257.

Left click on the line and drag it to add a new vertex. The vertex is placed wherever you release the left click button.

../../_images/poisson_add_vertex_cursor.png

Figure 257 The mouse cursor display when adding a vertex is possible

[Remove Vertex] (R)

Description: Deletes the vertex of lines.

When this is selected and you move the cursor onto the vertex of the lines, the cursor shape will change (Figure 258). Left clicking will remove the vertex.

../../_images/poisson_remove_vertex_cursor.png

Figure 258 The mouse cursor when removing the vertex is possible

[Edit Center Line Coordinates] (T)

Description: Edits the coordinates of [Center Line].

When you select the menu , the [Center Line Coordinates] dialog (Figure 259) will open. Edit the coordinates and click on [OK].

../../_images/poisson_coordinates_dialog.png

Figure 259 [Center Line Coordinates] dialog

[Edit Left Bank Line Coordinates] (C)

Description: Edits the coordinates of [Left Bank Line].

The procedure is the same to [Edit Center Line Coordinates] (T).

[Edit Right Bank Line Coordinates] (H)

Description: Edits the coordinates of [Right Bank Line].

The procedure is the same to [Edit Center Line Coordinates] (T).

[Reset to Default] (R)

Description: Discards the grid creating conditions and restores the default state.

[Import Center Line] (E)

Description: Import [Center Line] from Shape files or CSV files.

The dialog in Figure 260 is shown, so please select the file you want to import, and click on [Open] button.

../../_images/poisson_center_import_dialog.png

Figure 260 [Select file to import] dialog

[Import Left Bank Line] (L)

Description: Import [Left Bank Line] from Shape files or CSV files.

The procedure is the same to [Import Center Line] (E).

[Import Right Bank Line] (I)

Description: Import [Right Bank Line] from Shape files or CSV files.

The procedure is the same to [Import Center Line] (E).

[Export Center Line] (N)

Description: Export [Center Line] to Shape files or CSV files.

The dialog in Figure 261 is shown, so please specify the name of file you want to export, and click on [Save] button.

../../_images/poisson_center_export_dialog.png

Figure 261 [Select file to export] dialog

[Export Left Bank Line] (F)

Description: Export [Left Bank Line] to Shape files or CSV files.

The procedure is the same to [Export Center Line] (N).

[Export Right Bank Line] (G)

Description: Export [Right Bank Line] to Shape files or CSV files.

The procedure is the same to [Export Center Line] (N).