What is the significance of 3.4D products in surveying and mapping?

With the combination and continuous development of surveying and mapping technology and computer technology, maps are no longer limited to the previous models. Modern digital map is mainly composed of DOM (digital orthophoto map), DEM (digital elevation model), DRG (digital raster map), DLG (digital line drawing) and composite model.

I. Introduction

1, DOM (digital orthophoto map): The image 4D effect data generated from aerial photos and remote sensing images are corrected by pixels, and cropped according to the scope of the map. Its information is rich and intuitive, with good interpretability and measurability, from which physical geography and socio-economic information can be directly extracted.

2.DEM (Digital Elevation Model): Digital Elevation Model is a collection of numbers, which expresses the ups and downs of the ground through elevation. It can make perspective views and cross-sectional views, calculate the earthwork volume and count the surface coverage area, which can be used for terrain analysis related to elevation, visibility condition analysis and flood inundation area analysis.

3.DRG (Digital Grid Map): Digital Grid Map is a digital product in the form of paper topographic map grid. It can be used as a background related to other spatial information, used for data collection, evaluation and update, and integrated with DOM and DEM to derive new visual information.

4.DLG (digital line drawing): a vector data set stored in layers according to basic geographical elements on the existing topographic map. Digital line drawing contains both spatial information and attribute information, which can be used in construction planning, resource management, investment environment analysis and other aspects as well as as as the spatial positioning basis of professional information systems such as population, resources, environment, transportation and public security.

Second, the collection method

1, Digital Elevation Model (DEM):DEM data acquisition usually includes the following methods:

(1): ground measurement: use automatic recording distance measuring theodolite (commonly used electronic quick measuring theodolite or universal theodolite) for field measurement. This theodolite is generally equipped with a microprocessor, which can automatically record and display relevant data, and can also calculate various stations. The recorded data can be input into the computer through serial communication for processing.

(2) Digitization of existing maps: the method of digitizing information (such as contour lines) on existing maps with digitizers. At present, commonly used text digitizers include hand tracking digitizer and scanning digitizer.

(3): Space sensor: The global positioning system (GPS) combined with radar and laser altimeter is used to collect data. As early as 2000, after the space shuttle Endeavour completed its nine-day flight around the earth, it used high-tech technologies such as spaceborne imaging radar and synthetic aperture radar to collect the ground elevation information of the area where human beings can move normally (about 80% of the total area of the table). After processing, it can be made into digital elevation models and three-dimensional topographic maps.

The surveying and mapping results obtained in this plan have wide coverage, high precision and unified benchmarks. They are not only widely used in the civil field, but also have important value in military activities such as missile launch, battlefield management and logistics planning, so they are widely concerned by military circles and media in various countries.

2. Digital photogrammetry method: This is one of the most commonly used and effective methods to obtain DEM data. Manual, semi-automatic or full-automatic measurement is used to obtain data by using the attached automatic recording device (interface) stereo mapping instrument or stereo coordinate instrument, analytical mapping instrument and digital photography system.

3. Lidar +CCD camera: Lidar, also known as airborne lidar, is an airborne laser detection and ranging system installed on aircraft. It is a comprehensive application system of GPS (Global Positioning System), INS (Inertial Navigation System) and laser ranging. For example, ALTM3 100 system produced by Canada's OPTECH Company and LiteMapper5600 system produced by Germany's IGI Company, ALTM3 100 and LiteMapper5600 airborne laser scanning remote sensing systems also integrate CCD cameras to record the image information of detection points synchronously with the laser detection and ranging system.