Product(s):	OpenFlows FLOOD
Version(s):	10.03.01.01

Overview

This article will detail how to create a regular (constant spaced) computational grid in OpenFlows FLOOD and will include an example. To construct curvilinear grids please follow this tutorial: How to construct curvilinear grids in OpenFlows FLOOD. 

Method

When setting up a model simulation a 2D computational grid needs to be created, as this will specify the locations and resolutions of the 2D cells. This computational grid will be considered in the interpolation process for generating digital terrain model data file.

OpenFlows FLOOD is able to generate different types of grids, illustrated in the next figure:

Figure 1 – Different types of grids generated by OpenFlows FLOOD

As an example, we will create a simple constant-spaced grid.

• Open the Toolbox and double click on Grid -> Create Constant Spaced Grid.

This will open the “Constant Spaced Grid Tool” docked on the right of the main area. Your window should look like the one shown in the next figure.

 

Figure 2 – Create Constant Spaced Grid

 

An important aspect to take into account is that OpenFlows FLOOD supports 3 coordinate systems when creating a computational grid. The coordinates may be WGS84 Geographical coordinates, UTM WGS84 (if so the corresponding UTM zone must be defined), and a generic local coordinate system (reference in this tool as "Grid Coordinates"). 

When using the computational grid to create a digital terrain model by interpolating terrain elevations (from XYZ, raster, TIN) to the computational grid, FLOOD is automatically convert the terrain elevations coordinate system to either WGS84 Geographical coordinates or UTM WGS84 coordinates. If the generic local coordinate system, then the terrain elevations coordinate system must be the same as the computational grid, as no coordinate conversion can take place. Also, if this system is used, then the computational grid (and all the layers construct from the computational grid such as the digital terrain model data file, additional gridded data files and gridded results) will not be able to be automatically georeferenced in OpenFlows FLOOD Map window. Additional HDF gridded results will not be able to be loaded on to LumenRT for 4D rendering of FLOOD's results immersed in a reality model, as LumenRT can only read FLOOD's results that are written in Geographical coordinates WGS84. 

Please use the parameters detailed in the next figure:

Parameter	Value	Description
Coord.	Geographic Coordinates (the default)	Type of the coordinates to use. Options are geographic, UTM and metric (local) coordinates.
Origin X	15.44	X coordinate of the lower left corner.
Origin Y	47.06922	Y coordinate of the lower left corner.
Columns	351	Nº of columns of the grid
Rows	236	Nº of rows of the grid
dX	0.00002	Size of the grid cells along the X axis. Given in units of the coordinate system (in this case º).
dY	0.00002	Size of the grid cells along the Y axis. Given in units of the coordinate system (in this case º).
Angle	0.0	Rotation of the grid.

This will create a computational mesh with approximately 2 meter resolution (1º in the latitude 47 is approximately 100 km).

Keep in mind that if WGS84 Geographical coordinates are selected, dX and dY are give in decimal degrees. If UTM WGS84 or "Grid Coordinates" is chosen, then dX and dY are given in meters. It is not yet possible to create a computational grid in feet, although it is possible to load terrain elevations layers (XYZ or raster formats) using projections in feet to create a digital terrain model, even though the computational grid is given in meters. 

Then, you need to save the grid file, by clicking in the lower-right button . After this you will be prompted to define the target path and filename. 

When the tool closes, the grid remains loaded in the Map Window:

Figure 3 – Created grid / Map visualization