Object Features¶

This section presents the various features that pertain to a 3D object.

Units¶

Both the E3DObjectExtractor ^.NET ^Python parameters and the E3DObject ^.NET ^Python features are expressed in metric units.

For example: if the resolution of the input EZMap ^.NET ^Python is expressed in mm / pixel, the length parameter is expressed in mm.
Use the EZMap::GetResolution ^.NET ^Python and EZMap::SetResolution ^.NET ^Python accessors of the EZMap ^.NET ^Python to query and change its resolution.

All angles are expressed in degrees.

Object Plane and Base Plane¶

The E3DObjectExtractor ^.NET ^Python fits a plane to the pixels of each E3DObject ^.NET ^Python output:

Use E3DObject::GetPlane ^.NET ^Python to access this plane.

The E3DObjectExtractor ^.NET ^Python also tries to fit a plane to the pixels surrounding an E3DObject ^.NET ^Python

This plane is called the base plane.
It is an estimation of the local background around the object.
If there are too many undefined pixels in this area, the base plane is equal to the reference plane of the input EZMap ^.NET ^Python.

../../../_images/setting_objects_01.webp — Representation of the *base plane* and the *object plane*.¶

Bounding Box¶

The bounding box is the minimal enclosing rectangle for all the object positions.

It is oriented in the XY plane of the ZMap space (rotation around the Z axis of the ZMap).
Its rotation is used as the orientation of the object (see E3DObject::GetOrientation ^.NET ^Python).
Its X and Y sizes are the object length and width (see E3DObject::GetLength ^.NET ^Python and E3DObject::GetWidth ^.NET ^Python).
Its Z size is always in the Z axis of the ZMap direction.

../../../_images/setting_objects_02.webp — Representation of bounding boxes around 3D objects.¶

Length and Width¶

The length of an object is the largest dimension on the XY plane in the ZMap space. It is the same as the size of the major axis of the bounding box.

The width of an object is the smallest dimension on the XY plane in the ZMap space. It is the same as the size of the minor axis of the bounding box.

Use the E3DObjectExtractor::SetLengthRange ^.NET ^Python and the E3DObjectExtractor::SetWidthRange ^.NET ^Python accessors to set the ranges of allowed values for the length and the width.

Length and width of 3D objects in a ZMap.

Length and width of 3D objects in a point cloud.

Local and Reference Top Positions and Heights¶

The local top position of an object is the position (3D coordinates) of the point in the E3DObject ^.NET ^Python that is the furthest from the base plane.

The local height of an object is the distance between the local top position and the base plane.

The reference top position of an object is the position (3D coordinates) of the point in the E3DObject ^.NET ^Python that is the furthest from the reference plane.

The reference height of an object is the distance between the reference top position and the reference plane.

Reference height viewed in a point cloud representation.¶

If there are too many undefined pixels in the object surroundings:

The base plane is equal to the reference plane of the input EZMap ^.NET ^Python.
The local top position is equal to the reference top position.
The local height is equal to the reference height.

Use the E3DObjectExtractor::SetLocalHeightRange ^.NET ^Python and the E3DObjectExtractor::SetReferenceHeightRange ^.NET ^Python accessors to set the ranges of allowed values for the local and the reference height.

Average Position¶

The average position is the arithmetic mean of the 3D positions of the object, also known as the barycenter.

../../../_images/setting_objects_07.webp — The average position is displayed in blue. The top position is displayed in red. The object on the left shows the average and the top positions at the same place. The object in the center shows the average position inside the object.¶

Aspect Ratio¶

The aspect ratio is the width (the smallest dimension on the XY plane) divided by the length (the largest dimension).

It lies between 0 and 1.
The smaller the ratio, the more elongated the object is.
A square has an aspect ratio of 1.

Use the E3DObjectExtractor::SetAspectRatioRange ^.NET ^Python accessor to set the range of allowed values for the aspect ratio.

../../../_images/setting_objects_08.webp — Aapect ratios of different objects in a ZMap representation.¶

Orientation Angle¶

The orientation angle is the angle between the X axis of the EZMap ^.NET ^Python and the longest axis (the length) of the object.

The angle is measured in the clockwise direction.
The value must lie between \(-90°\) and \(+90°\).

Use the E3DObjectExtractor::SetOrientationRange ^.NET ^Python accessor to set the range of allowed values for the orientation angle.

../../../_images/setting_objects_09.webp — Representation angle viewed in a ZMap representation.¶

Local and Reference Tilt Angles¶

The local tilt angle is the angle between the base plane and the object plane.

A value of 0 means that the object top surface is parallel to its base.
The value must lie between \(0°\) and \(+90°\).

The reference tilt angle is the angle between the object plane and ZMap XY plane.

A value of 0 means that the object top surface is parallel to its base.
The value must lie between \(0°\) and \(+90°\).

Use the E3DObjectExtractor::SetLocalTiltRange ^.NET ^Python and the E3DObjectExtractor::SetReferenceTiltRange ^.NET ^Python accessors to set the range of allowed values for the tilt angles.

Area¶

The object area is the area of the top surface of the object projected on the reference plane of the EZMap ^.NET ^Python.

It is equal to the number of pixels in the object × the x-resolution of the EZMap ^.NET ^Python × the y-resolution of the EZMap ^.NET ^Python.

Use the E3DObjectExtractor::SetAreaRange ^.NET ^Python accessor to set the range of allowed values for the area.

../../../_images/setting_objects_12.webp — Area of an object in a point cloud representation.¶

Volume¶

The object volume is the volume that lies between the top surface and the base plane of the object.

Use the E3DObjectExtractor::SetVolumeRange ^.NET ^Python accessor to set the range of allowed values for the volume.

../../../_images/setting_objects_13.webp — Volume of an object in a point cloud representation.¶

Sphere¶

This feature is disabled by default.

When enabled, a sphere is an object E3DSphere ^.NET ^Python that represents the sphere that best fits the object (calculated according to the least squares).