LiDAR's applications and uses

USGS's 3D Elevation Program (3DEP)

• USGS's 3DEP: complete LiDAR coverage for the entire country by 2023
• Total project cost: $ 1 billion

USGS data on Entwine

USGS's 3D Elevation Program (3DEP)

• USGS identified 600 applications potentially benefit from 3DEP data

USGS Updates on 3DEP (April 24 2019)

USGS's 3D Elevation Program (3DEP)

• USGS identified 600 applications potentially benefit from 3DEP data

USGS updates on 3DEP (April 24 2019)

Business uses of LiDAR data (ordered by estimated annual benefits)

• Flood risk management (FEMA)
• Infrastructure and construction management
• Natural resources conservation (NEON)
• Agriculture and precision farming
• Water supply and quality
• Wildfire management, planning and response
• Geologic resource assessment and hazard mitigation
• Forest resources management
• River and stream resource management
• Aviation navigation and safety
• ...
• Land navigation and safety

Source: USGS Updates on 3DEP (April 24 2019)   LiDAR applications and business uses factsheets

LiDAR data

a brief look under the hood

• LiDAR datasets are often referred to as "3D point clouds" - sets of spatially coherent, 3D points.
• In its simplest form, a LiDAR point cloud is a table of coordinates and numeric values, in which each row (tuple) contains the 3 coordinates of each sampling point (x, y, z) and optionally several additional point attributes.

LiDAR data

a brief look under the hood

• There are 2 types of point attributes: scalar (one-dimensional), and vector (multi-dimensional)
• Examples of additional attributes:
  • Timestamp: a time tag value at which the point was acquired
  • Intensity, reflectance, amplitude: a numeric value representing the (normalized) laser pulse return magnitude
  • Number of returns (target count): the total number returns for a given pulse
  • Return number (target ID): the pulse return number for a given output pulse
  • True color: often in (red, green, blue) format
  • Surface normal vector: often in (n_x, n_y, n_z) format

LiDAR data in text formats

• Human readable and highly interoperable
• Not optimal for machine interpretation and manipulation.
• Generic CSV (comma-separated-values), TSV (tab-separated-values) formats can be used to store LiDAR data.
• Metadata (e.g. total number of points) can be stored in the beginning and/or the end of each file.

LiDAR data in binary formats

• Not human readable, and requires file format specification for interoperability
• Optimized for machine interpretation and often more compact
• Examples: LAS, E57

ASPRS's LAS format

• A standard file format developed and maintained by the ASPRS (American Society of Photogrammetry and Remote Sensing)
• General structure:
  • Metadata (header and variable length records)
  • Sequence of point records
  • Additional metadata

ASPRS's LAS format

ASPRS's LAS format

• A standard file format developed and maintained by the ASPRS (American Society of Photogrammetry and Remote Sensing)

ASPRS's LAS format

Think twice (or more) about your selection of a data representation

• Be concious about the number of decimal digits you keep.

IEEE 754

Think twice (or more) about your selection of a data representation

• Beware of the limitations of your selection of data types (e.g. IEEE 754 floating point number encoding).
  • Not every real number can be represented by a IEEE 754 float.
  • There is always a gap between 2 consecutive representable numbers. The gap increases as we move away from number zero.
  • Example 1: the next representable float number after 0.085000000894070 is 0.085000008344650; there is a gap of 0.000000007450581 between the two numbers.
  • Example 2: the next representable float number after 182536128.0 is 182536192.0; there is a gap of 64.0 between the two numbers.

IEEE 754

Think twice (or more) about your selection of a data representation

• Beware of the limitations of your selection of data types (e.g. IEEE 754 floating point number encoding).
  • "95% of folks out there are completely clueless about floating-point." -- James Gosling
  • The first launch of Arian 5 (European space rocket) failed because of a similar problem.

IEEE 754