gen_measure_arc (Operator)

Name

`gen_measure_arc` — Prepare the extraction of straight edges perpendicular to an annular arc.

Signature

`gen_measure_arc( : : CenterRow, CenterCol, Radius, AngleStart, AngleExtent, AnnulusRadius, Width, Height, Interpolation : MeasureHandle)`

Description

`gen_measure_arc` prepares the extraction of straight edges which lie perpendicular to an annular arc. Here, annular arc denotes a circular arc with an associated width. The center of the arc is passed in the parameters `CenterRow` and `CenterCol`, its radius in `Radius`, the starting angle in `AngleStart`, and its angular extent relative to the starting angle in `AngleExtent`. If `AngleExtent` > 0, an arc with counterclockwise orientation is generated, otherwise an arc with clockwise orientation. The radius of the annular arc, i.e., half its width, is determined by `AnnulusRadius`.

For an explanation of the concept of 1D measuring see the introduction of chapter 1D Measuring.

The edge extraction algorithm is described in the documentation of the operator `measure_pos`. As discussed there, different types of interpolation can be used for the calculation of the one-dimensional gray value profile. For `Interpolation` = 'nearest_neighbor', the gray values in the measurement are obtained from the gray values of the closest pixel, i.e., by constant interpolation. For `Interpolation` = 'bilinear', bilinear interpolation is used, while for `Interpolation` = 'bicubic', bicubic interpolation is used.

To perform the actual measurement at optimal speed, all computations that can be used for multiple measurements are already performed in the operator `gen_measure_arc`. For this, an optimized data structure, a so-called measure object, is constructed and returned in `MeasureHandle`. The size of the images in which measurements will be performed must be specified in the parameters `Width` and `Height`.

The system parameter 'int_zooming' (see `set_system`) affects the accuracy and speed of the calculations used to construct the measure object. If 'int_zooming' is set to 'true', the internal calculations are performed using fixed point arithmetic, leading to much shorter execution times. However, the geometric accuracy is slightly lower in this mode. If 'int_zooming' is set to 'false', the internal calculations are performed using floating point arithmetic, leading to the maximum geometric accuracy, but also to significantly increased execution times.

Attention

Note that when using bilinear or bicubic interpolation, not only the measurement rectangle but additionally the margin around the rectangle must fit into the image. The width of the margin (in all four directions) must be at least one pixel for bilinear interpolation and two pixels for bicubic interpolation. For projection lines that do not fulfill this condition, no gray value is computed. Thus, no edge can be extracted at these positions.

Please also note that the center coordinates of the arc are rounded internally, so that the center lies on the pixel grid. This is done to ensure consistency.

Execution Information

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Processed without parallelization.

This operator returns a handle. Note that the state of an instance of this handle type may be changed by specific operators even though the handle is used as an input parameter by those operators.

Parameters

`CenterRow` (input_control)  point.y `→` (real / integer)

Row coordinate of the center of the arc.

Default value: 100.0

Suggested values: 10.0, 20.0, 50.0, 100.0, 200.0, 300.0, 400.0, 500.0

Typical range of values: ```0.0 ≤ CenterRow ≤ 511.0``` (lin)

Minimum increment: 1.0

Recommended increment: 10.0

`CenterCol` (input_control)  point.x `→` (real / integer)

Column coordinate of the center of the arc.

Default value: 100.0

Suggested values: 10.0, 20.0, 50.0, 100.0, 200.0, 300.0, 400.0, 500.0

Typical range of values: ```0.0 ≤ CenterCol ≤ 511.0``` (lin)

Minimum increment: 1.0

Recommended increment: 10.0

`Radius` (input_control)  number `→` (real / integer)

Default value: 50.0

Suggested values: 10.0, 20.0, 50.0, 100.0, 200.0, 300.0, 400.0, 500.0

Typical range of values: ```0.0 ≤ Radius ≤ 511.0``` (lin)

Minimum increment: 1.0

Recommended increment: 10.0

`AngleStart` (input_control)  angle.rad `→` (real / integer)

Start angle of the arc in radians.

Default value: 0.0

Suggested values: -3.14159, -2.35619, -1.57080, -0.78540, 0.0, 0.78540, 1.57080, 2.35619, 3.14159

Typical range of values: ```-3.14159 ≤ AngleStart ≤ 3.14159``` (lin)

Minimum increment: 0.03142

Recommended increment: 0.31416

`AngleExtent` (input_control)  angle.rad `→` (real / integer)

Angular extent of the arc in radians.

Default value: 6.28318

Suggested values: -6.28318, -5.49779, -4.71239, -3.92699, -3.14159, -2.35619, -1.57080, -0.78540, 0.78540, 1.57080, 2.35619, 3.14159, 3.92699, 4.71239, 5.49779, 6.28318

Typical range of values: ```-6.28318 ≤ AngleExtent ≤ 6.28318``` (lin)

Minimum increment: 0.03142

Recommended increment: 0.31416

Restriction: `AngleExtent != 0.0`

`AnnulusRadius` (input_control)  number `→` (real / integer)

Radius (half width) of the annulus.

Default value: 10.0

Suggested values: 10.0, 20.0, 50.0, 100.0, 200.0, 300.0, 400.0, 500.0

Typical range of values: ```0.0 ≤ AnnulusRadius ≤ 511.0``` (lin)

Minimum increment: 1.0

Recommended increment: 10.0

Restriction: `AnnulusRadius <= Radius`

`Width` (input_control)  extent.x `→` (integer)

Width of the image to be processed subsequently.

Default value: 512

Suggested values: 128, 160, 192, 256, 320, 384, 512, 640, 768

Typical range of values: ```0 ≤ Width ≤ 1024``` (lin)

Minimum increment: 1

Recommended increment: 16

`Height` (input_control)  extent.y `→` (integer)

Height of the image to be processed subsequently.

Default value: 512

Suggested values: 120, 128, 144, 240, 256, 288, 480, 512, 576

Typical range of values: ```0 ≤ Height ≤ 1024``` (lin)

Minimum increment: 1

Recommended increment: 16

`Interpolation` (input_control)  string `→` (string)

Type of interpolation to be used.

Default value: 'nearest_neighbor'

List of values: 'bicubic', 'bilinear', 'nearest_neighbor'

`MeasureHandle` (output_control)  measure `→` (handle)

Measure object handle.

Result

If the parameter values are correct, the operator `gen_measure_arc` returns the value TRUE. Otherwise an exception is raised.

Possible Predecessors

`draw_circle`

Possible Successors

`measure_pos`, `measure_pairs`, `fuzzy_measure_pos`, `fuzzy_measure_pairs`, `fuzzy_measure_pairing`

Alternatives

`edges_sub_pix`

`gen_measure_rectangle2`