About mesh editing

InfoWorks ICM has many tools available to enhance the detail of 2D meshes, beyond simply representing the topology from the ground model. Use mesh editing objects from external GIS files, layers displayed on the GeoPlan view, or objects within the network.

2D mesh considerations

When adding 2D mesh editing objects to a model, there are a few things to keep in mind:

• If building detail into a mesh beyond a single street level, good quality GIS mapping is needed as the base data. Then, extract, clean, and simplify the information into GIS files to be imported into ICM.
• Use the 2D Zone properties as an advantage. At a certain point, too much data will represent a problem. On large catchments, polygons can be built for the entirety of the 2D zone, and then imported. However, many of those polygons share the same key property, such as the infiltration model, but differ spatially. This is where the 2D Zone properties can be advantageous, by setting it to a specific value and omitting importing those polygons.

• Data should be simplified to remove excessive vertices before being imported. If 2D elements are 5m2, there is typically little value in having vertices spaced less than 0.5m apart.
• The addition of new objects requires the mesh to be regenerated before they are applied, and this must be done before a simulation can take place.
• The majority of objects are automatically included in the mesh during generation once they have been added to the network—except for voids and breaklines, which must be explicitly allocated.

• Ideally, object types should be added one at a time to simplify conflict resolution. When adding thousands of polygons into a model and recreating a mesh, problems or errors can be difficult to isolate. Therefore, it is always best to add object types, such as roughness zones, one at a time, and then re-mesh to ensure there are no problems.

Simplifying external GIS layers

There are some things that can be done to simplify external GIS layers before they are imported into ICM.

In adjoining buildings, there is the potential for vertex conflicts. If individual building footprints share the same threshold, or they are outside the area of interest, then they can be merged into a single polygon. This can significantly simplify the quantity and complexity of input data. However, in areas of interest, this may not always be possible.

Reduce excessive vertices. There is typically not much benefit to having individual vertices at spacings less than 0.5m, especially along straight edges. Reducing the vertex count can help to speed up digitization of the GeoPlan.

Post import considerations

Once the import process is complete and the model is ready to be worked on, other mesh-editing considerations may come up:

• Multi-part, hollow, or donut polygons should be avoided, as they can be difficult for the mesher to interpret correctly. Use the 2D zone properties to help simplify inputs and eliminate the need to store polygon objects with the same properties in the model.
• Gaps between buildings and any other mesh features can generate many elements with the classic meshing routine. Remove or expand these gaps as appropriate.
• Complex shapes contain many points and may require several stages of refinement. This is best undertaken in specialist GIS software, where the proper tools and routines are available to process large datasets more easily.
• If a high-level of detail is required for outputs, it can be simpler to achieve this via post-processing than by building this level of detail into the model.

Refinement questions

Asking some questions about the needs of the specific model can help to refine it. For example:

What level of detail is required for the outputs?
Can the level of detail vary in different regions of the model?
Do all the buildings and structures need modelling explicitly?

Answering these questions can help to determine the next steps.