BaseHatcher

class pyslm.hatching.BaseHatcher

Bases: ABC

The BaseHatcher class provides common methods used for generating the ‘contour’ and infill ‘hatch’ scan vectors for a geometry slice typically a multi-polygon region.

The class provides an interface to generate a variety of hatching patterns used. The developer should re-implement a subclass and re-define the abstract method, BaseHatcher.hatch(), which will be called as a minimum. Other behavior can be controlled for the generation of scan vectors include generateHatching().

The user typically specifies a boundary, which may be offset the boundary of region using offsetBoundary(). This is typically performed before generating the infill. Following offsetting, then a series of hatch lines are generated using generateHatching() to fill the entire boundary region using polygonBoundingBox(). To obtain the final clipped infill, the hatches are clipped using clipLines() which are clipped in the same sequential order they are generated using a technique explained further in the class method. The generated scan paths should be stored into collections of LayerGeometry accordingly.

Attributes Summary

CLIPPER_SCALEFACTOR

The scaling factor used for polygon clipping and offsetting in PyClipr for the decimal component of each polygon coordinate.

Methods Summary

boundaryBoundingBox(boundaries)

Returns the bounding box of a list of provided boundaries, typically generated by the tree representation in pyclipr.

clipContourLines(paths, contourPaths)

clipLines(paths, lines)

clipperToHatchArray(coords)

error()

Returns the accuracy of the polygon clipping depending on the chosen scale factor.

generateHatching(paths, hatchSpacing[, ...])

Generates un-clipped hatches which is guaranteed to cover the entire polygon region base on the maximum extent of the polygon bounding box

hatch(boundaryFeature)

The hatch method should be re-implemented by a child class to generate a Layer containing the scan vectors used for manufacturing the layer.

offsetBoundary(paths, offset)

Offsets a single path for a single polygon.

offsetPolygons(polygons, offset)

Offsets a set of boundaries across a collection of polygons by the offset distance.

polygonBoundingBox(obj)

Returns the bounding box of the polygon - typically this represents a single shape with an exterior and a list of boundaries within an array.

Attributes Documentation

CLIPPER_SCALEFACTOR: int = 100000

The scaling factor used for polygon clipping and offsetting in PyClipr for the decimal component of each polygon coordinate. This should be set to inverse of the required decimal tolerance i.e. 0.01 requires a minimum scale factor of 100. This scaling factor is used in internally in ClipperLib2.

Note:

From experience, 1e4, mostly works, however, there are some artefacts generated during clipping hatch vectors. Therefore at a small performance cost 1e5 is recommended.

Methods Documentation

static boundaryBoundingBox(boundaries)

Returns the bounding box of a list of provided boundaries, typically generated by the tree representation in pyclipr. The output of the bounding box takes the form of \(\left(x_{min}, y_{min}, z_{min}, x_{max}, y_{max}, z_{max}\right)\).

Parameters:

boundaries – A list of polygons

Return type:

array

Returns:

A \((1 \times 6)\) numpy array of the bounding box

static clipContourLines(paths, contourPaths)

This function clips a series of (contour paths) across a closed polygon using Pyclipr.

Note

The order is guaranteed from the list of lines used, so these do not require sorting. However, the position may require additional sorting to cater for the user’s requirements.

Parameters:

  • paths – The set of boundary paths for trimming the lines

  • contourPaths (List[ndarray]) – The un-trimmed complex open paths to be clipped

Returns:

A list of trimmed lines (open paths)

static clipLines(paths, lines)

This function clips a series of lines (hatches) across a closed set of polygons using Pyclipr.

Note

The order is guaranteed from the list of lines used, so these do not require sorting usually. However, the position may require additional sorting to cater for the user’s requirements during scanning.

Parameters:

  • paths – The set of boundary paths for trimming the lines

  • lines – The untrimmed lines to clip from the boundary

Returns:

A list of trimmed lines (open paths)

static clipperToHatchArray(coords)

A helper method which converts the raw polygon edge lists returned by PyClipr into a numpy array.

Parameters:

coords (ndarray) – The list of hatches generated from clipping operations

Return type:

array

Returns:

The hatch coordinates transfromed into a \((n \times 2 \times 3)\) numpy array.

classmethod error()

Returns the accuracy of the polygon clipping depending on the chosen scale factor.

Return type:

float

generateHatching(paths, hatchSpacing, hatchAngle=90.0)

Generates un-clipped hatches which is guaranteed to cover the entire polygon region base on the maximum extent of the polygon bounding box

Parameters:

  • paths – The boundary paths for the generated hatch vectors to cover

  • hatchSpacing (float) – Hatch spacing to use

  • hatchAngle (Optional[float]) – Hatch angle (degrees) to rotate the scan vectors

Return type:

ndarray

Returns:

Returns the list of un-clipped scan vectors

abstractmethod hatch(boundaryFeature)

The hatch method should be re-implemented by a child class to generate a Layer containing the scan vectors used for manufacturing the layer.

Parameters:

boundaryFeature – The collection of boundaries of closed polygons within a layer.

Raises:

NotImplementedError

Return type:

Optional[Layer]

static offsetBoundary(paths, offset)

Offsets a single path for a single polygon.

Parameters:

  • paths – Closed polygon path list for offsetting

  • offset (float) – The offset applied to the poylgon

Returns:

A list of boundaries offset from the subject

static offsetPolygons(polygons, offset)

Offsets a set of boundaries across a collection of polygons by the offset distance. A positive offset is the offset applied to the exterior of the polygon, whereas a negative offset is applied to the interior of the boundary.

Note

Note that if any polygons are expanded overlap with adjacent polygons, the offsetting will NOT unify into a single shape.

Parameters:

  • polygons – A list of closed polygons which are individually offset from each other.

  • offset (float) – The offset distance applied to the polygon

Returns:

A list of boundaries offset from the subject

static polygonBoundingBox(obj)

Returns the bounding box of the polygon - typically this represents a single shape with an exterior and a list of boundaries within an array. The output of the bounding box takes the form of \(\left(x_{min}, y_{min}, z_{min}, x_{max}, y_{max}, z_{max}\right)\).

Parameters:

obj (Any) – A set of geometries

Return type:

ndarray

Returns:

A \((1 \times 6)\) numpy array representing the bounding box of a polygon