What is photogrammetry? Why can photogrammetry draw topographic maps?

Photogrammetry refers to the technology of measuring the shape, size and spatial position of the target by combining camera and film. Since 1839, when Nips and Dale invented photography, photogrammetry has a history of 170 years.

1. camera: In photogrammetry, the camera used to obtain aerial images is called aerial camera. Aerial cameras usually include photosensitive elements (i.e., negatives or digital cameras), lenses and mechanical structures.

2. External orientation element: used to determine the orientation of each photo in the ground space, including the geographic coordinates of the photography center and the camera attitude (i.e. rotation angle and direction).

3. Internal orientation elements: parameters used to determine the position and size of object points in each photo, including camera image point, image distance, distortion, etc.

4. Image: refers to a photo or digital image obtained and recorded by a camera in aerial photography or space photography, which shows the characteristics of the ground.

5. Stereo matching refers to the matching, orientation and fusion of two or more photos obtained from the same target or area in the same ground coordinate system to obtain a three-dimensional model and a digital map.

6. Digital Surface Model (DSM): A terrain surface model obtained from stereo images and modeled by digital technology can be used to accurately measure terrain elevation and terrain attributes.

7. Orthophoto: refers to a two-dimensional orthographic image that can be accurately measured and analyzed by correcting and integrating images with different heights and angles.

Matters needing attention when using photogrammetry technology

1, Safety first: Photogrammetry often involves flying, erecting equipment and other activities, so it is necessary to strictly abide by safety specifications and operating procedures to ensure that people or things will not be harmed during the operation.

2. High accuracy requirements: The data results of photogrammetry affect the accuracy and accuracy of the whole surveying and mapping, and the requirements are very high, so careful planning and preparation are needed before any operation, and high-precision equipment and tools are needed.

3. Data selection and processing: Photogrammetry needs a lot of data, and the selection and processing of data has a great influence on the accuracy and precision of the results, so it is necessary to select and process the data reasonably to avoid data clutter and interference.