06 Grids

DELFT-FEWS is a location oriented system. All time series data must be referenced to a (geographic) location. Scalar time series need no additional information. For grid time series data, each point in the grid must be referenced to a location in a grid structure.

Grids may be regular or irregular. In regular grids each cell has the same width, height and area within the coordinate system it is specified in.

In irregular grids the grid has a fixed number of rows and columns, but the cell height and width is not equal in each row and column. For these grids additional information is required on the location of each individual cell in the grid to allow display in the grids display as well as for use in the spatial interpolation routine.

When available on the file system, the name of the XML file is for example:

Grids 1.00 default.xml

Grids                                          Fixed file name for the Grids configuration

1.00                                            Version number

default                                       Flag to indicate the version is the default configuration (otherwise omitted).

Figure 28 Elements of the grids configuration

regular

Definition of a regular grid. One or more regular grids may be defined.

Attributes;

•         locationId; location Id of the grid. This locationId must be included in the locations definition.

irregular

Definition of a irregular grid. One or more irregular grids may be defined.

Attributes;

•         locationId; location Id of the grid. This locationId must be included in the locations definition.

Regular grids

Figure 29 Elements of the Regular Grid in the Grids configuration

description

Optional description of the grid. Used only for reference purposes

rows, columns

Number of rows and columns in the grid

geoDatum

Coordinate system the grid is defined in. This may be a different coordinate system to that used in the main map display. The coordinate system may also differ per grid, as a grid may be regular in one coordinate system, but may be irregular in another. Defining the grid in the regular coordinate system is easier.

firstCellCenter

Coordinates of the center of the first grid cell. The convention in DELFT-FEWS is that this is the center point of the top left cell in the grid (Upper-Left).

firstCellCenter: x

Geographic coordinate of the first cell center point (Easting)

firstCellCenter: y

Geographic coordinate of the first cell center point (Northing)

firstCellCenter: z

Optional elevation of the first cell center point (Easting). If only this elevation is defined , then all cells in the grid are assumed to have the same elevation.

xCellSize / columnWidth

Cell width of each column in the grid. The cell width is given in the unit of the coordinate system referred to in the geoDatum. Generally this is metres, but in WGS 1984 this is decimal degrees.

The xCellSize-element is used when all cells are equal in width. Please use the columnWidth-element to define cells with variable columnWidth.

yCellSize / rowHeigt

Cell height of each row in the grid. The cell height is given in the unit of the coordinate system referred to in the geoDatum. Generally this is metres, but in WGS 1984 this is decimal degrees.

The yCellSize-element is used when all cells are equal in height. Please use the rowHeight-element to define cells with variable height.

z / zBottom / zTop

Optional definition of the elevation of each point in the grid. This definition is only necessary where a datum is required in for example 3-dimensional interpolation. This may be applied in for example interpolating temperature grids in high mountain areas. Alternative uses are the display of elevation in a cross section of the Spatial Display. The bottom/top layer is only displayed if the parameter unit is meters and if the corresponding displayOptions are configured in the TimeSeriesDisplayConfig file and if the layer contains non-NaN values. The useDatum property is not used here.

Use 'z' for the average elevation, and zBottom and zTop in case a model layer needs to be defined

zMapLayerName / zBottomMapLayerName / zTopMapLayerName

Optional definition of the elevation by reference to an ASC or BIL file stored in the MapLayerFiles-directory. This definition is only necessary where a datum is required in for example 3-dimensional interpolation. This may be applied in for example interpolating temperature grids in high mountain areas. Alternative uses are the display of elevation in a cross section of the Spatial Display. The bottom/top layer is only displayed if the parameter unit is meters and if the corresponding displayOptions are configured in the TimeSeriesDisplayConfig file and if the layer contains non-NaN values. The useDatum property is not used here.

Use 'zMapLayerNAme' for the average elevation, and zBottomMapLayerName and zTopMapLayerName in case a model layer needs to be defined.

Irregular grids

Figure 30 Elements of the irregular grid in the Grids configuration

description

Optional description of the grid. Used only for reference purposes

rows, columns

Optional, when specified the grid cell boundaries can be based on the neighbour cells. Number of rows and columns in grid, at least two rows and two columns. Don't configure this for scattered point grids.

geoDatum

Coordinate system the grid is defined in. This may be a different coordinate system to that used in the main map display. The coordinate system may also differ per grid. A grid may be regular in one coordinate system, but may be irregular in another. Defining the grid in the regular coordinate system is generally easier.

cellCentre

Definition of the cell centre points of all cells in the irregular grid. The number of cellCentre points defined must be the same as the number of cells in the grid (rows x columns).

cellCentre: x, cellCentre: y

Geographic coordinates of the cell centre point (x: Easting, y: Northing).

cellCentre: z

Elevation of the cell centre point.

esriShapeFile

Shape file with cell polygons, lines and/or cell centers.

csvFile

Since 2013.01. Csv file with cell centers.

netcdfFile

Since 2015.02. Reference to a NetCDF file that contains only grid geometry meta data. This only supports mesh topologies (unstructured grids) with 2D coordinates. This can be 1D network, 2D triangular, 2D flexible or 3D layered mesh topologies. For more information see https://github.com/ugrid-conventions/ugrid-conventions

Irregular grid definition from a UGRID NetCDF file

file

Name of a NetCDF file in the map layer files or a full absolute path to a NetCDF file. The file must have extension ".nc".

geoDatum

Optional. If the geoDatum of the coordinates cannot be determined from the infromation in the NetCDF file, then this geoDatum will be used. If this geoDatum is also not specified, then WGS 1984 will be used by default.

meshTopologyVariableName

Name of a mesh topology variable in the NetCDF file that contains the meta-data attributes of the mesh on which the data is defined.

staggerLocation

The (stagger) location within the mesh at which the data is defined. Only node, edge and face are supported. Data defined at nodes or edges will be handled as points in FEWS. Data defined at faces will be handled as polygons in FEWS. If the mesh in the netcdf file does not contain valid face bound coordinate variables, then data defined at faces will be handled as points in FEWS.

locationIndexSetVariableName

Name of a location index set variable in the NetCDF file that contains the indices of the locations at which the data is defined. The location index set variable in the NetCDF file should point to a mesh topology variable and a (stagger) location within the mesh. This is only supported if the location index set variable in the NetCDF file contains coordinates (i.e. a coordinates attribute that points to coordinate variables that contain only coordinates for the index set, not for the entire mesh).

Using a UGRID NetCDF file as unstructured grid definition

To import/export unstructured grid/flexible mesh data in Delft-FEWS, use a timeSeriesImport/ExportRun with type "NETCDF-CF_GRID" or use a generalAdapter import/exportNetcdfActivity. For this to work you need to add an irregular grid definition to the grids.xml configuration file. The easiest way to do this, is by using the option "netcdfFile" (see above) that refers to a NetCDF file that contains a UGRID mesh topology (and no data).

It is possible to use a D-Flow flexible mesh (D-Flow FM) flowgeom UGRID NetCDF file, produced by a D-Flow FM model run, as grid definition in Delft-FEWS. If your D-Flow FM model run does not produce a flowgeom file, then add the following line in the D-Flow FM .mdu file in the output section, e.g.:

[output]
...
FlowGeomFile    = f34_flowgeom.nc    # *_flowgeom.nc Flow geometry file in NetCDF format.
...

If the produced flowgeom file is not in UGRID NetCDF format, then you can change the format to UGRID NetCDF by changing the MapFormat to 4 in the D-Flow FM .mdu file in the output section:

[output]
...
MapFormat    = 4    # Map file format, 1: netCDF, 2: Tecplot, 3: netCFD and Tecplot, 4: NetCDF-UGRID
...

The flowgeom file format matches the map file format.

Config Examples

<irregular locationId="meshLocation">
	<netcdfFile>
		<file>simplebox_hex7_map.nc</file>
		<meshTopologyVariableName>insert_mesh_variable_name_here</meshTopologyVariableName>
		<staggerLocation>face</staggerLocation>
	</netcdfFile>
</irregular>

<irregular locationId="Swan2D_G2_cellcenters">
	<rows>1318</rows>
	<columns>317</columns>
	<esriShapeFile>
		<file>swan2D_G2_cellcenters.shp</file>
		<geoDatum>WGS 1984</geoDatum>
		<x>%X%</x>
		<y>%Y%</y>
	</esriShapeFile>
</irregular>

<irregular locationId="Swan2D_G2_cellcenters">
	<rows>1318</rows>
	<columns>317</columns>
	<esriShapeFile>
		<file>swan2D_G2_cellcenters.shp</file>
		<projectionFileAvailable>true</projectionFileAvailable>
		<x>%X%</x>
		<y>%Y%</y>
	</esriShapeFile>
</irregular>

<regular locationId="KNMI-HIRLAM-V70">
	<description>grid def. for KNMI-HIRLAM v7.0 with rotated pole</description>
	<rows>226</rows>
	<columns>136</columns>
	<rotatedSouthPole>
		<latitude>-30</latitude>
		<longitude>-15</longitude>
	</rotatedSouthPole>
	<gridCorners>
		<geoDatum>WGS 1984</geoDatum>
		<upperLeft>
			<x>-30.8688</x>
			<y>79.63847</y>
		</upperLeft>
		<lowerRight>
			<x>10.29617</x>
			<y>26.065</y>
		</lowerRight>
	</gridCorners>
</regular>

<regular locationId="WRF_CWB_Grid">
	<description>grid def. for imported WRF_CWB data</description>
	<rows>178</rows>
	<columns>148</columns>
	<geoDatum>WGS 1984</geoDatum>
	<firstCellCenter>
		<x>117.358656</x>
		<y>28.752274</y>
	</firstCellCenter>
	<xCellSize>0.048912529</xCellSize>
	<yCellSize>0.048912529</yCellSize>
</regular>

<regular locationId="QPF_LR">
		<description>QPF Grid for Long RangeABRFC</description>
	<rows>689</rows>
	<columns>1073</columns>
	<lambertConformalConic>
		<originLatitude>25.0</originLatitude>
		<originLongitude>265.0</originLongitude>
		<firstStandardParallelLatitude>25.0</firstStandardParallelLatitude>
		<secondStandardParallelLatitude>25.0</secondStandardParallelLatitude>
	</lambertConformalConic>
	<gridCorners>
		<geoDatum>WGS 1984</geoDatum>
		<upperLeft>
			<x>-130.13937712795388</x>
			<y>49.958437615088435</y>
			<z>0.0</z>
		</upperLeft>
		<lowerRight>
			<x>-69.19419381895221</x>
			<y>20.30332235930985</y>
			<z>0.0</z>
		</lowerRight>
	</gridCorners>
</regular>

<regular locationId="QPF">
	<description>QPF Grid for ABRFC</description>
	<rows>159</rows>
	<columns>335</columns>
	<polarStereographic>
		<originLatitude>90.0</originLatitude>
		<originLongitude>-105.0</originLongitude>
		<scaleAtOrigin>0.933</scaleAtOrigin>
		<equatorRadius>6367470.0</equatorRadius>
		<poleRadius>6367470.0</poleRadius>
	</polarStereographic>
	<gridCorners>
		<geoDatum>WGS 1984</geoDatum>
		<upperLeft>
			<x>-106.67471389477944</x>
			<y>39.37455858318055</y>
			<z>0.0</z>
		</upperLeft>
		<lowerRight>
			<x>-92.34455929643786</x>
			<y>32.390342856654044</y>
			<z>0.0</z>
		</lowerRight>
	</gridCorners>
</regular>

Generating XML

For NetCDF and GRIB files you can generate the grids.xml with F12>Clipboard>Copy grib geometry form file