A point cloud geometry is a (potentially large) collection of points. Point clouds are useful for storing large amounts of data, often gathered from LIDAR applications.
Associated with each point are properties called components, which contain a value that describes the point. Components are similar to attributes, but at the point level instead of at the feature level. Note that all points in a point cloud have the same schema (that is, the same set of components), but each point may have a different value for each component.
All components have a name and type. Possible component types are Real64, Real32, UInt64, UInt32, UInt16, UInt8, Int64, Int32, Int16, Int8, and String. Numeric components additionally may have a scale and offset factor; in such cases, the applied value of the component is
value x scale + offset. String components additionally may have an encoding.
While components may have any name, there are a few common components that exist in several formats. These components are described in the following table.
|x||The x component of the geometry.|
|y||The y component of the geometry.|
|z||The z component of the geometry.|
|intensity||The magnitude of the intensity of the pulse return.|
|color_red||The red image channel value at the point.|
|color_green||The green image channel value at the point.|
|color_blue||The blue image channel value at the point.|
|classification||The class of the point. Categorizes a point into fields, such as ground, building, water, and others. Values correspond to the ASPRS LAS specification.|
|return||The pulse return number for a given output pulse.|
|number_of_returns||The total number of detected returns from a single pulse.|
|gps_time||The number of seconds since the beginning of the week.|
|gps_week||The week number, counting from January 6th, 1980.|
|angle||The angle of the pulse that the point was scanned at.|
|flight_line||The flight line number the point was detected in.|
|flight_line_edge||Whether this point lies on the edge of the scan, along the flight line.|
|scan_direction||The direction in which a scanning mirror was directed when the point was detected.|
|point_source_id||A value that indicates the source of the file, such as a file number.|
|posix_time||Used to express the time, as the number of seconds elapsed since UTC January 1st, 1970.|
|user_data||Data to be used at the user’s discretion.|
|normal_x||The x component of the vertex normals.|
|normal_y||The y component of the vertex normals.|
|normal_z||The z component of the vertex normals.|
Indicates special characteristics associated with each point. Values correspond to the ASPRS LAS specification.
Note that there are no required components. For example, point clouds typically have all of the x/y/z components, but a point cloud may not have z (making it 2D), or may not have any of x/y/z (making it non-spatial).
Point clouds may also store a 4x4 transformation matrix, which is applied to the x/y/z components.
Point Cloud Attributes
- fme_geometry = fme_polygon
- fme_type = fme_point_cloud