When it comes to height, various uncertainties arise as in other departments. This uncertainty in GIS is due to the existence of a wide range of elevation models and not knowing which one to use in our project.
DSM (Digital Surface Models), DEM (Digital Elevation Models), DTM (Digital Terrain Models) and even TIN (Triangular Irregular Networks) are among the most widely used methods.
DSM (Digital Surface Models)
In LiDAR system, light pulses go to the ground. When the pulse of light comes out of its target and returns to the sensor, it gives the range (variable distances) to the earth.
Finally, LiDAR offers a large point cloud filled with variable altitude values. However, these elevation values may come from the top of buildings, tree canopy, power lines and other features. A DSM captures natural and artificial features on the Earth’s surface.
DSM is suitable for 3D modeling for telecommunications, city planning and aviation. Since the objects are removed from the ground surface, the following projects will be good examples.
Runway Approach Zone Execution: In aviation, DSMs can identify runway obstacles in the approach zone.
Vegetation Management: Throughout a transmission line, DSMs can see where vegetation occupies the line and how much of the line is occupied.
Field of View Inference: Urban planners use DSM to control how a proposed building will affect the visibility of residents and businesses.
DEM (Numerical Height Models)
DEM consists of raster grids that refer to a vertical datum and represent the naked world.
Artificial (power lines, buildings and towers) and natural (trees and other types of vegetation) elements are not included in a DEM. When you filter out off-land spots such as bridges and roads, you override artificial formations and vegetation, you get a smooth DEM.
This model is used extensively in hydrology, land and land use planning.
Hydrological Modeling: Hydrologists use DEMs to clean basins and calculate flow accumulation and flow direction.
Balancing Land Destruction: The areas prone to screaming are high sloping areas with sparse vegetation. This application is useful in planning the motorway or residential subdivision.
Soil Mapping: DEMs help mapping soils (such as geology, time and climate), a height function.
DTM (Digital Terrain Models)
Looking at the USGS LiDAR Base Specification (page 28), a DTM can be defined in two different ways, depending on where you live.
In some countries, a DTM is actually synonymous with a DEM. In other countries such as the United States and Turkey has a different meaning to the DTM. DTM is a vector data set consisting of dots at regular intervals and natural features such as mountain ridge and breaking lines (a line in the model showing a marked cut in the slope of a surface, such as a road or stream). DTM strengthens DEM by adding linear properties to bare soil terrain.
DTMs are typically generated by stereo photogrammetry. In the example, the contour lines are purple. DTM points are placed at regular intervals and characterize the shape of the bare soil area.
In the next picture you can see how the DTM is not continuous and not a surface model. You can include a DTM in a DEM from regular spacing and contour lines. A DTM shows distinctive terrain characteristics much better due to 3D refraction lines and 3D mass points at regular intervals.
How to Obtain Elevation Models Data
Some of the remote sensing methods that can be used to generate elevation models are:
LIDAR: As a result of the light coming out of the device hitting the ground, the reflected surface is returned to the sensor to measure the height of the ground surface.
Satellite Interaction: Synthetic aperture radars, such as Shuttle Radar Topography Mission, use two radar images simultaneously captured antennas to create a DEM.
Photogrammetry: Aerial photography uses photographs taken from at least two different points with photogrammetry. Similar to the operation of vision in humans, it can obtain depth and perspective due to separate perspectives.