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Mesh Visualisation

The plot_mesh_normals function renders the mesh with element outlines and normal arrows coloured by physical group, so you can check normal orientation before computing. It is provided as an optional extension built on Plots.jl — loading Plots triggers it automatically.

Setup

using Plots
using RadiativeViewFactor

If Plots is not loaded, calling plot_mesh_normals raises a clear error message rather than a cryptic MethodError.

Basic usage

mesh = load_mesh("geometry.msh"; surface_dim=1)
fig  = plot_mesh_normals(mesh)

The normal scale is estimated automatically from the mesh bounding box and the element count. The result is a 2D Plots.Plot with equal aspect ratio and one legend entry per group (name and tag).

Curve meshes (surface_dim=1) are the primary use: Line3 elements are drawn as smooth quadratic curves, Line2 as straight segments, and each element has a normal arrow at its midpoint.

Surface meshes (surface_dim=2) are drawn as an xy-projection of the element edges and normals — a quick sanity check, not a 3-D view. For full 3-D inspection of a surface mesh use Gmsh's built-in normal visualisation (View → Mesh → Normals).

Options

fig = plot_mesh_normals(mesh;
    normal_scale  = 0.05,              # arrow length in mesh units
    show_nodes    = true,              # scatter-plot element nodes
    show_indices  = true,              # label each element with its index
    group_colors  = Dict(1=>:red,      # override colours per physical group tag
                         2=>:blue))

normal_scale must be a Float64 (write 1.0, not 1).

Saving to file

fig = plot_mesh_normals(mesh)
savefig(fig, "normals.pdf")
savefig(fig, "normals.png")

Interpreting the output

Each element is drawn as:

  • A line (Line2, Line3) or edge outline (Tri3, Quad4, Tri6, Quad8) in the group colour
  • An arrow at the element centre (midpoint, for curve elements) pointing along the element normal

Arrows pointing toward the opposing surface indicate correct orientation. Arrows pointing away indicate a winding error — use reverse_normals=true in load_mesh to flip all normals before computing view factors, or reverse_group_normals to flip selected groups.