Package 'trowel'

Edit a live mesh

Description

Points are added with mesh_add_points() (returning stable vertex ids; a point at an existing vertex returns that vertex's id). Segments join two vertex ids; a segment that crosses an existing constraint has the crossing inserted as a new vertex, with attributes interpolated along the new segment. Removing a point removes any segment through it; removing a segment clears its constraint edges and leaves the vertices.

Usage

mesh_add_points(m, x, y, PA = NULL)

mesh_add_segments(m, a, b)

mesh_remove_points(m, ids)

mesh_remove_segments(m, seg_ids)

Arguments

m	a mesh from mesh_new()
x, y	coordinates of points to add
PA	attribute matrix for the new points (one row per point), or NULL
a, b	vertex ids of segment endpoints
ids	vertex ids to remove
seg_ids	segment ids to remove

Value

vertex ids for mesh_add_points, segment ids for mesh_add_segments, the mesh invisibly for the removals

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Create a live mesh

Description

A persistent constrained Delaunay triangulation that accepts edits at any time. Start empty or from the usual three tables: vertices, segments as index pairs, optional per-vertex attributes.

Usage

mesh_new(x = NULL, y = NULL, s0 = NULL, s1 = NULL, PA = NULL)

Arguments

x, y	vertex coordinates (may be omitted for an empty mesh)
s0, s1	1-based indices into the vertices for constraint segments
PA	numeric matrix of per-vertex attributes (one row per vertex), or NULL; column names become attribute names

Value

a trowel handle (a mutable object: functions that edit it return it invisibly)

Examples

x <- c(0, 1, 1, 0, 0.25, 0.75, 0.75, 0.25)
y <- c(0, 0, 1, 1, 0.25, 0.25, 0.75, 0.75)
m <- mesh_new(x, y, 1:8, c(2, 3, 4, 1, 6, 7, 8, 5))
mesh_counts(m)
table(mesh_triangles(m)$depth)

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Read a live mesh as tables

Description

Read a live mesh as tables

Usage

mesh_vertices(m)

mesh_triangles(m)

mesh_segments(m)

mesh_constraint_edges(m)

mesh_edges(m)

mesh_counts(m)

Arguments

m

a mesh

Value

data frames: mesh_vertices (id, x, y, origin, attribute columns; origin is "input", "crossing" or "steiner"), mesh_triangles (v0, v1, v2 as vertex ids, depth = constraint crossings from outside), mesh_segments (segment, position, vertex: the chain of vertex ids along each live segment), mesh_constraint_edges and mesh_edges (a, b vertex ids); mesh_counts is a list of sizes.

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Refine a live mesh

Description

Delaunay refinement toward a minimum angle and/or a maximum triangle area, inserting Steiner vertices. Attributes on new vertices are interpolated linearly from the mesh as it was before refinement. Can be called again after further edits.

Usage

mesh_refine(
  m,
  min_angle = NULL,
  max_area = NULL,
  max_steiner = Inf,
  keep_constraints = FALSE,
  inner_only = TRUE
)

Arguments

m	a mesh
min_angle	minimum angle in degrees (NULL for none; spade caps at 30)
max_area	maximum triangle area (NULL for none)
max_steiner	budget of Steiner vertices (Inf for unlimited)
keep_constraints	if TRUE constraint edges are never split
inner_only	if TRUE (default) the region outside every constraint (depth 0) is left as it was: Steiner vertices that would land there are dropped (vertices on boundary constraint edges stay, since they belong to both sides). Holes count as inside; filter by depth parity yourself if a hole should not be refined. FALSE refines every triangle in the hull.

Value

invisibly, a list with complete (did refinement finish within budget), added (vertex count added) and new_ids

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Triangle vertex index matrix

Description

Convenience for plotting and for handing to code that wants 1-based row indices into mesh_vertices() rather than ids.

Usage

mesh_T(m)

Arguments

m

a mesh

Value

integer matrix, 3 columns, rows index into mesh_vertices(m)

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The live mesh.

Description

The live mesh.

Usage

Trowel

Format

An object of class environment of length 12.

Methods

Method new

Create an empty mesh, with optional attribute column names.

Method add_points

Add points; returns their ids (an existing vertex at the same position is reused).

Method add_segments

Add constraint segments between existing vertex ids; crossings with existing constraints are resolved by inserting the crossing point. Returns segment ids.

Method remove_points

Remove vertices by id. Segments through them are removed too.

Method remove_segments

Remove segments by id (constraint flags cleared; vertices stay).

Method refine

Refine the mesh. Any argument may be NA to skip it.

Method vertices

Vertices: id, x, y, origin (0 input, 1 crossing, 2 steiner), attributes.

Method triangles

Triangles as vertex ids (3 columns) plus depth.

Method constraint_edges

Constraint edges currently in the mesh, as vertex id pairs.

Method edges

All edges as vertex id pairs.

Method segments

User segments: segment id and the chain of vertex ids along it.

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