Circular No. 17/2019/TT-BTNMT stipulates technical procedures for establishing digital elevation models using terrestrial LiDAR scanning technology on fixed stations.

CIRCULAR

Technical regulations for establishing digital elevation models using terrestrial LiDAR scanning technology on fixed stations
Ground-based LiDAR at fixed stations

Pursuant to the Law on Surveying and Mapping dated June 14, 2018;

Pursuant to Decree No. 27/2019/NĐ-CP dated March 13, 2019 of the Government detailing certain provisions of the Law on Surveying and Mapping;

Pursuant to Decree No. 36/2017/NĐ-CP dated April 4, 2017 of the Government on the functions, tasks, powers, and organizational structure of the Ministry of Natural Resources and Environment;

At the proposal of the Director of the Vietnam National Survey, Mapping and Geoinformation Agency, the Director of the Institute of Surveying and Mapping Sciences, the Head of the Science and Technology Department, and the Head of the Legal Department;

The Minister of Natural Resources and Environment promulgates this Circular on technical regulations for establishing digital elevation models using terrestrial LiDAR scanning technology on fixed stations,

PART I

GENERAL PROVISIONS

Article 1. Scope of Regulation

This Circular stipulates technical requirements for establishing digital elevation models using terrestrial LiDAR scanning technology on fixed stations.

Article 2. Applicability

This Circular applies to state management agencies in surveying and mapping; organizations and individuals operating in the field of surveying and mapping.

Article 3. Explanation of Terms

In this Circular, the following terms are understood as follows:

1. TIN (Triangular Irregular Network): A special format used to store digital elevation model data in the form of an irregular triangular grid.

2. GeoTIFF: A special format used to store digital image data along with geographic location information of the image; raster DEM and DSM data.

3. Fixed station point: A point where the LiDAR scanning equipment is placed and has coordinates and height accuracy equivalent to that of the first-order control network.

4. Control measurement point: A point where control measurements are set up to link scanning data from adjacent fixed stations.

5. Terrestrial LiDAR scanning on fixed stations: A method using LiDAR scanning equipment placed on fixed stations to create 3D models of surfaces and objects.

Chapter II

TECHNICAL REGULATIONS

Article 4. Mathematical Basis

1. Digital elevation models shall be established according to the National Reference System and National Coordinate System VN-2000, projection, and central meridian as specified in Circular No. 973/2001/TT-TCĐC dated June 20, 2001 of the Land Administration General Department guiding the application of the national reference system and coordinate system VN-2000.

2. The elevation system used in building digital elevation models is the national elevation system.

Article 5. Accuracy requirements for digital elevation models

Digital elevation models shall be established with accuracy requirements as specified in Table 1 below:

Article 6. Procedures for establishing digital elevation models using ground-based LiDAR scanning technology at fixed stations

Article 6. Procedure for establishing digital elevation models using terrestrial LiDAR scanning technology on fixed stations

The procedure for establishing digital elevation models using terrestrial LiDAR scanning technology on fixed stations includes the following main steps:

Step 1. Preparation work;

Step 2. Site survey;

Step 3. Design of terrestrial LiDAR scanning;

Step 4. Control measurement;

Step 5. Data acquisition;

Step 6. Data processing;

Step 7. Field investigation, verification, and supplementary surveying;

Step 8. Establishment of digital elevation models;

Step 9. Quality inspection, review, and acceptance;

Step 10. Product delivery.

Article 7. Preparation work

1. Collection of documents and data: topographic maps, land administration maps..., collection of national coordinate and height control points, Geoid model (if available) in the construction area.

2. Preliminary plan preparation: determination of the data acquisition range of a single station and scan point density, drawing the layout of station placement points on the topographic map.

3. Preparation of computers and software for SS adjustment, leveling, and LiDAR data processing.

Article 8. Site Survey

1. On-site handover of the construction site area.

2. Topographic and topographical survey of the construction site area: describe the characteristics of the terrain and topography such as elevation differences, terrain fragmentation, and density of topographical features to adjust the preliminary design for detailed design purposes.

3. Determine national coordinate points and elevations to serve the control network measurement for coordinates and elevations.

Article 9. Design for Ground-based LiDAR Scanning

1. Design LiDAR stations according to the principle that adjacent stations must be aligned; scanning coverage must fully cover the construction site area; ensure maximum accuracy and cost-effectiveness. The station scanning point density is determined per square kilometer. The data acquisition range of a single scanning station and the station scanning point density are specified in Table 2 as follows:

(*) - For requirements to establish a high-precision Digital Elevation Model (DEM) with accuracies of 0.10 m and 0.20 m, the distance between adjacent stations shall not exceed 400 m.

2. Design target points according to the following principles:

a) Between two adjacent stations, at least five common target points must be arranged, and these points should not lie on a straight line;

b) Target points are designed in circular or square shapes with dimensions no less than 15 cm, coated with reflective paint to enhance surface reflectivity for laser beams.

Article 10. Control Network Measurement

1. The ground-based LiDAR scanning control network established at fixed stations is formed using surveying technologies ensuring accuracy equivalent to a first-order base network for station points.

2. The accuracy of station points is defined as follows:

a) The coordinates of station points are determined with accuracy equivalent to a first-order base network;

b) The height accuracy of station points is determined to be equivalent to technical height networks.

3. Design marker points for station machines and measure the coordinates and heights of station points

a) Specifications and sizes of markers for station machines follow the regulations for second-order network survey markers in Appendix 01 of Circular No. 68/2015/TT-BTNMT dated December 22, 2015, issued by the Minister of Natural Resources and Environment regarding direct survey techniques for topographic mapping and geographic base database establishment at scales of 1:500, 1:1000, 1:2000, and 1:5000 (hereinafter referred to as Circular No. 68/2015/TT-BTNMT);

b) First-order base networks and technical height networks are stipulated in Circular No. 68/2015/TT-BTNMT.

Article 11. Data Acquisition for LiDAR

1. The LiDAR scanning equipment must be accurately centered and balanced, measuring the machine height twice at the beginning and end of each session, reading to millimeters.

2. At adjacent station points, target points must be accurately centered and balanced using tripods. Measure the height of the target points, reading to millimeters.

3. Establish parameters for a station: station point number, coordinates, and height; adjacent station point numbers, coordinates, and heights of target points.

4. Requirements during on-site scanning:

a) During scanning, continuously monitor the operation of all equipment;

b) At each station, record the logbook: scanning time, scanning mode, draw a schematic diagram of the station including information about the station point number, adjacent station point numbers, and target point numbers according to the provisions in the Appendix attached to this Circular;

c) The minimum number of scanning points when acquiring data must be 100 points per square meter;

d) After completing each station, check that the recorded data is fully stored in the scanner's memory.

Article 12. Data Processing

The process of processing ground-based LiDAR scanning data at fixed stations includes the following main steps:

1. Loading data into the computer.

2. Filtering out points exceeding the data reception limit of a single station machine.

3. Merging point cloud data from individual station machines and conducting relative offset checks at common measurement points between adjacent station machines. The relative offset between common measurement points shall not exceed twice the permissible error specified in Table 1.

4. Merging and adjusting point cloud data from individual station machines into a unified block based on coordinate and height parameters of the station points.

5. Removing points that do not belong to the target for data collection.

6. Classifying point cloud data for establishing digital surface models and digital elevation models.

Article 13. Field Survey, Cross-checking, and Supplementary Measurement

1. Identifying areas lacking scanning data for establishing digital elevation models due to obstruction, weak signals, interference, or flooded areas.

2. Conducting supplementary measurements using methods such as electronic total stations, GNSS, and other equivalent methods. The density and accuracy of supplementary measurement points are regulated in Article 30 of Circular No. 68/2015/TT-BTNMT.

3. Processing and integrating supplementary measurement data with LiDAR scanning data.

Article 14. Establishing Digital Elevation Models

1. Digital elevation models are created from groups of digital elevation model data.

2. Digital elevation models are represented in TIN, GRID, or GeoTIFF formats.

3. The accuracy requirements for established digital elevation models are as follows:

a) Edge errors between measurement zones must not exceed 1.5 times the permissible error of the digital elevation model;

b) Absolute errors of the digital elevation model are evaluated through field check points. The root mean square error of the height difference between measured heights and digital elevation model heights must not exceed the accuracy requirement specified in Table 1. Limit errors must not exceed twice the root mean square error and must not exceed 10%.

Article 15. Quality Inspection, Review, and Acceptance

Quality inspection, review, and acceptance work are carried out according to the provisions of Circular No. 24/2018/TT-BTNMT dated November 15, 2018, issued by the Minister of Natural Resources and Environment regarding quality inspection, review, and acceptance of surveying and mapping products.

Article 16. Submission of Data and Products

Submitted products include:

1. All original data from the LiDAR scanning device.

2. Point cloud data files in LAS format.

3. Grayscale images.

4. Digital surface models stored in two binary GRID and ASCII formats.

5. Digital elevation models stored in three binary GRID formats, TIFF format, and ASCII format with metadata or other formats if required.

6. Field measurement results: control grids for coordinates and heights of the measurement area, supplementary measurements (if applicable).

7. Technical summary report detailing information about equipment and software used, control grid adjustment results, LiDAR scanning parameters, point classification and filtering results, evaluation of processing errors, technical parameters of the digital elevation model.

Chapter III

IMPLEMENTING PROVISIONS

Article 17. Effective Date

1. This Circular takes effect from November 15, 2019.

2. When referenced documents in this Circular are amended, supplemented, or replaced, they shall be applied according to the newly issued documents.

Article 18. Responsibility for Implementation

1. Ministries, ministerial-level agencies, government-affiliated agencies, provincial People's Committees, centrally governed cities, and related organizations and individuals are responsible for implementing this Circular.

2. During implementation, if there are difficulties, agencies, organizations, and individuals should reflect them to the Ministry of Natural Resources and Environment for consideration and decision./.