Topographical perspective or land surveying perspective is asurvey is taken of surface features of the earth (for example, mountainous regions, etc); this can be obtained from an aeroplane flight using a LIDAR image capture system. Images must later be processed to extract vertical dimension data, and the results can then be viewed on a digital display, such as Google Maps or Google Earth.
Digital Elevation Model
A Digital Elevation Model (DEM) is a 3-D representation of a planetary surface’s topography, showing “bare earth” by removing objects. DEMs are crucial for GIS analysis, hydrological modelling, and infrastructure planning, derived from sources like satellite radar, LiDAR, and topographic maps.
Key Aspects
- Definition: DEMs represent bare earth, while DSMs include surface features.
- Data Sources: Generated from NASA’s SRTM, ASTER, and LIDAR surveys.
- Applications: Used in flood risk mapping, infrastructure, agriculture, and forestry.
- Visualisation & Processing: Techniques like hill-shading and slope analysis enhance terrain.
- Errors: Issues include “sinks” and “peaks,” needing correction for hydrologic modelling.
Common Types
- SRTM: NASA radar data for 80% of land.
- ASTER GDEM: Global DEM from satellite imagery.
- Copernicus DEM: High-res global DEM at 30m resolution.
- LiDAR DTM: Accurate ground elevation from laser scanning.
Digital Terrain Model
A Digital Terrain Model (DTM) represents the bare earth’s topography, excluding objects like trees and buildings. It consists of a 3-D grid of elevation points, often from LiDAR, and is crucial for flood risk assessment, civil engineering, and landscape visualisation.
Topological Map
A topological map perspective presents essential connections and structure, simplifying reality by removing precise scale and detail to show relationships, for example with subway maps highlighting routes over exact geography. Wheres the topographic map perspective, uses contour lines to visually translate a 3-D landscape’s elevation and terrain (hills, valleys) onto a flat 2-D surface, crucial for navigation and understanding landforms.
Stereo Mapping
Stereo mapping is a photogrammetric technique that uses two overlapping aerial or satellite images of the same area taken from different angles to create a 3-D, stereoscopic view. It enables accurate measurement and 3-D feature extraction—such as topography, buildings, and infrastructure—for GIS and engineering projects. This process, often viewed using glasses or specialised screens, provides superior visualisation compared to 2-D, allowing for precise, interactive, and detailed 3-D mapping.