measure_pairs — Extract straight edge pairs perpendicular to a rectangle or annular arc.
measure_pairs(Image : : MeasureHandle, Sigma, Threshold, Transition, Select : RowEdgeFirst, ColumnEdgeFirst, AmplitudeFirst, RowEdgeSecond, ColumnEdgeSecond, AmplitudeSecond, IntraDistance, InterDistance)
measure_pairs serves to extract straight edge pairs
which lie perpendicular to the major axis of a rectangle or
For an explanation of the concept of 1D measuring see the introduction of chapter 1D Measuring.
The extraction algorithm of
is identical to
measure_pos. In addition
the edges are grouped to pairs: If
Transition = 'positive',
the edge points with a dark-to-light transition in the direction of the major
axis of the rectangle are returned in
ColumnEdgeFirst. In this case, the corresponding edges with a
light-to-dark transition are returned in
Transition = 'negative', the
behavior is exactly opposite. If
Transition = 'all', the
first detected edge defines the transition for
ColumnEdgeFirst. I.e., dependent on the positioning of the measure
object, edge pairs with a light-dark-light transition or edge pairs with a
dark-light-dark transition are returned. This is suited, e.g., to measure
objects with different brightness relative to the background.
If more than one consecutive edge with
the same transition is found, the first one is used as a pair element. This
behavior may cause problems in applications in which the threshold
Threshold cannot be selected high enough to suppress consecutive
edges of the same transition. For these applications, a second pairing mode
exists that only selects the respective strongest edges of a sequence of
consecutive rising and falling edges. This mode is selected by appending
'_strongest' to any of the above modes for
e.g., 'negative_strongest'. Finally, it is possible to select which
edge pairs are returned. If
Select is set to 'all', all
edge pairs are returned. If it is set to 'first', only the first of
the extracted edge pairs is returned, while it is set to 'last',
only the last one is returned.
The extracted edges are returned as single points which lie on the
major axis of the rectangle. The corresponding edge amplitudes are
In addition, the distance between each edge pair is returned in
IntraDistance and the distance between consecutive edge
pairs is returned in
InterDistance. Here, IntraDistance[i]
corresponds to the distance between EdgeFirst[i] and EdgeSecond[i],
while InterDistance[i] corresponds to the distance between
EdgeSecond[i] and EdgeFirst[i+1], i.e., the tuple
InterDistance contains one element less than the tuples
of the edge pairs.
measure_pairs only returns meaningful results if the
assumptions that the edges are straight and perpendicular to the
major axis of the rectangle are fulfilled. Thus, it should not be
used to extract edges from curved objects, for example.
Furthermore, the user should ensure that the rectangle is as close
to perpendicular as possible to the edges in the image. Additionally,
Sigma must not become larger than approx. 0.5 * Length1
(for Length1 see
It should be kept in mind that
measure_pairs ignores the
Image for efficiency reasons. If certain regions
in the image should be excluded from the measurement a new measure
object with appropriately modified parameters should be generated.
→object (byte / uint2 / real)
Measure object handle.
Sigma of gaussian smoothing.
Default value: 1.0
Suggested values: 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 7.0, 10.0
Typical range of values:
Minimum increment: 0.01
Recommended increment: 0.1
Sigma >= 0.4
Minimum edge amplitude.
Default value: 30.0
Suggested values: 5.0, 10.0, 20.0, 30.0, 40.0, 50.0, 60.0, 70.0, 90.0, 110.0
Typical range of values:
Minimum increment: 0.5
Recommended increment: 2
Type of gray value transition that determines how edges are grouped to edge pairs.
Default value: 'all'
List of values: 'all', 'all_strongest', 'negative', 'negative_strongest', 'positive', 'positive_strongest'
Selection of edge pairs.
Default value: 'all'
List of values: 'all', 'first', 'last'
Row coordinate of the center of the first edge.
Column coordinate of the center of the first edge.
Edge amplitude of the first edge (with sign).
Row coordinate of the center of the second edge.
Column coordinate of the center of the second edge.
Edge amplitude of the second edge (with sign).
Distance between edges of an edge pair.
Distance between consecutive edge pairs.
If the parameter values are correct the operator
returns the value 2 (H_MSG_TRUE). Otherwise an exception is raised.