Mesh Level Zones
Mesh Level Zone objects are used as part of the mesh generation process carried out when undertaking 2D modelling. They can be used to divide a 2D Zone into regions in which mesh element elevations are to be modified based on ground level elevations or user-defined values. The zones can be used to define elevations of road channels and kerb depths for example.
Mesh Level Zones can be imported via the Open Data Import Centre or, for InfoWorks networks, generated via intersection. Zones can also be digitised directly on the GeoPlan Window.
Parameters for Mesh Level Zones are edited in the Mesh Level Zone Grid Window of the Polygons Grid or the Mesh Level Zone Property Sheet. For further information on creating and editing polygons, see the Digitising Network Objects section.
Using Mesh Level Zones for Ground Level Adjustment
Mesh Level Zones can be used to define specific zones in which ground levels are to be modified in the 2D mesh.
The ground level at each zone vertex is determined from the Ground Model used during the meshing process or from user-defined values.
Adjustments to zone vertex levels are applied and mesh element elevations within the zone are calculated from the resulting surface instead of the ground model. Elevations are assigned to mesh elements within the zone without modifying the source ground model.
The method of adjustment is selected in the Type field, and are described below:
- Level (Specified fixed level): the level of all Mesh Level Zone elements and vertices will be set to the value specified in the Level field.
- Rel. to highest (Fixed level relative to highest): the maximum sampled level from the ground model within the Mesh Level Zone is found, and then raised or lowered by a value specified in the Raise by field.
- Rel. to lowest (Fixed level relative to lowest): the minimum sampled level from the ground model within the Mesh Level Zone is found, and then raised or lowered by a value specified in the Raise by field.
- Raise or lower: the level of every Mesh Level Zone element and vertex is raised or lowered by a value specified in the Raise by field.
- Specify (Specified boundary elevations): the elevations at mesh level zone vertices will be set to a user defined value, obtained from the ground model or interpolated from other zone vertices as specified in the Vertices grid. The calculated elevations will then be adjusted by an Elevation adjustment specified in the grid.
- Adjust (Boundary ground model adjusted): the elevations at mesh level zone vertices will be set from the ground model and will then be adjusted by the Elevation adjustment specified in the Vertices grid.
If you use either the Specify (Specified boundary elevations)or Adjust (Boundary ground model adjusted) option, you can also specify that Upper limit level and Lower limit level values are to be applied. If the modified element level is greater than the upper limit or less than the lower limit, the element level will be set to the value in the limit field.
When the 2D mesh is generated, the Level (Specified fixed level), Rel. to highest (Fixed level relative to highest), and Rel to lowest (Fixed level relative to lowest) options will produce a Mesh Level Zone surface that is perfectly flat while Raise or lower simply raises or lowers the ground level of the zone without altering its surface.
The Specify (Specified boundary elevations) and Adjust (Boundary ground model adjusted) options let you change the topography of the Mesh Level Zone as individual vertex elevations can be adjusted.
See the Mesh Level Zone Data Fields (InfoWorks) and the Mesh Level Zone Data Fields (SWMM) topics for details about the criteria used to adjust element ground levels.
The adjusted ground level is displayed in the Ground Level field of the 2D Zone Mesh Element Properties dialog.
If changes are made to a Mesh Level Zone after meshing of the 2D zone has been carried out, it will be necessary to recalculate mesh elevations within the 2D zone. This can be done by resampling elevations for selected 2D zones.
