Help-Desk

LiDAR is an active remote sensing system. An active system means that the system itself generates energy - in this case, light - to measure things on the ground. In a LiDAR system, light is emitted from a rapidly firing laser. You can imagine light quickly strobing from a laser light source. This light travels to the ground and reflects off of things like buildings and tree branches. The reflected light energy then returns to the LiDAR sensor where it is recorded.

A LiDAR system measures the time it takes for emitted light to travel to the ground and back. That time is used to calculate distance traveled. Distance traveled is then converted to elevation. These measurements are made using the key components of a lidar system including a GPS that identifies the X,Y,Z location of the light energy and an Internal Measurement Unit (IMU) that provides the orientation of the plane in the sky.

There are many different types of LiDARs based on their functionality and inherent characteristics.

• Airborne LiDAR
• Topographic LiDAR
• Terrestrial LiDAR
• Bathymetric LiDAR

A Discrete Return LiDAR System records individual (discrete) points for the peaks in the waveform curve. Discrete return LiDAR systems identify peaks and record a point at each peak location in the waveform curve. These discrete or individual points are called returns. A discrete system may record 1-4 (and sometimes more) returns from each laser pulse.

A Full Waveform LiDAR System records a distribution of returned light energy. Full waveform LiDAR data are thus more complex to process however they can often capture more information compared to discrete return LiDAR systems.

To get a high-quality orthomosaic map, you need high-quality images. To get high-quality images, you need to plan for a number of different variables, and develop a flight plan that creates the right conditions to handle them.

Without a defined and catalogued flight plan, even the most detailed aerial images lack important context needed to build an orthomosaic composite that is reliable, detailed, and accurate. That’s where flight planning comes in.

A drone flight plan will ideally be uniform in every possible sense, from elevation above a target object or landmass to airspeed and camera angle. Automation helps make the physical maneuvering of the drone easier, but without a carefully researched and detailed flight plan, the images you capture will end up with distortion that undermines accuracy and usability of the final map.

Post-processed spatially organized lidar data is known as point cloud data. The initial point clouds are large collections of 3D elevation points, which include x, y, and z, along with additional attributes such as GPS time stamps. The specific surface features that the laser encounters are classified after the initial lidar point cloud is post-processed. Elevations for the ground, buildings, forest canopy, highway overpasses, and anything else that the laser beam encounters during the survey constitutes point cloud data.

While LiDAR is a technology for making point clouds, not all point clouds are created using LiDAR. For example, point clouds can be made from images obtained from digital cameras, a technique known as photogrammetry. The one difference to remember that distinguishes photogrammetry from LiDAR is RGB. In other words: colour. Photogrammetric point clouds have an RGB value for each point, resulting in a colourised point cloud. On the other hand, when it comes to accuracy, LiDAR is hard to beat.

Photogrammetry and LiDAR (light detection and ranging) can produce similar outputs. Understanding their technological differences is crucial for land surveyors and geospatial professionals.

In drone survey missions, the choice between photogrammetry and LiDAR depends heavily on the exact application. You also need to consider operational factors, such as cost and complexity. Knowing what outputs you really need will help you make the right decision.

How does photogrammetry work?

In photogrammetry, a drone captures a large number of high-resolution photos over an area. These images overlap such that the same point on the ground is visible in multiple photos and from different vantage points. In a similar way that the human brain uses information from both eyes to provide depth perception, photogrammetry uses these multiple vantage points in images to generate a 3D map. The result: a high-resolution 3D reconstruction that contains not only elevation/height information, but also texture, shape, and color for every point on the map, enabling easier interpretation of the resulting 3D point cloud. Drone systems that use photogrammetry are cost effective and provide outstanding flexibility in terms of where, when, and how you capture 2D and 3D data.

How does LIDAR work?

LiDAR, which stands for “light detection and ranging,” is a technology that has been around for many decades but has only recently been available in a size and power feasible for carrying on large drones. A LIDAR sensor sends out pulses of laser light and measures the exact time it takes for these pulses to return as they bounce from the ground. It also measures the intensity of that reflection.

Comparison table: Photogrammetry and LiDAR

• Land surveying / cartography
• Land management and development
• Precise measurements
• Slope monitoring
• Stockpile volumetric measurements
• Urban planning

Land survey services are asked to produce topographic surveys for:

• construction and architectural projects
• environmental restoration and property improvements
• to fulfill regulatory requirements for construction codes
• guidance for setting up grading or drainage ditches
• when land developed for one purpose is being used for another purpose

Topographic maps identify numerous ground features, which can be grouped into the following categories:

• Relief: mountains, valleys, slopes, depressions as defined by contours Hydrography: lakes, rivers, streams, swamps, rapids, falls
• Vegetation: wooded areas Transportation: roads, trails, railways, bridges, airports/airfield, seaplane anchorages
• Culture: buildings, urban development, power ransmission line, pipelines, towers
• Boundaries: international, provincial/territorial, administrative, recreational, geographical
• Toponymy: place names, water feature names, landform names, boundary names

Refer to the map legend for a complete listing of all features and their corresponding symbols. Information along the map borders provides valuable details to help you understand and use a topographic map. For example, here you will find the map scale and other important information about the map such as the year, the edition and information pertaining to the map data.

Normally, a topographic survey is used as a basis for design decisions. An architect or consulting engineer will need an accurate digital plan of their site area to produce good design and construction drawings. The survey and data can also be used for other purposes, including new housing developments, new road layouts, land registry submissions or volumetric calculations.

Bathymetric contours are similar to regular contours, except they depict the elevations, shape, and slope of marine features offshore (usually the bottom floors of bays, seas, and oceans). They should not be confused with maps that depict depth curves, which usually represent water depths along coast~ lines and inland bodies of water. The contours of these maps are usually show in blue, with the data coming from hydrographic charts and depth soundings.

Ref://geologyscience.com" target="_blank">Google

All construction takes place in or on the ground, so it is easy to see how geotechnical engineering plays a crucial role in all civil engineering projects. Before any construction work takes place, it is vitally important to do a site investigation. The degree of investigation, impacts of the soil, and the overall need for a subsurface investigation vary greatly depending on the type of project.

Geotechnical survey helps you to design economical foundations and foundations suitable to particular soils and its conditions. Thus, prevents the failure of structures by both excessive settlements and load carrying failure.

Geo Technical Order (GTO) is a very important piece of document in oil well drilling. The subsurface data (formation boundaries, pressure, objective etc.) are the basis on which drilling plan is prepared. On this basis casing policy and mud systems are designed. The GTO includes everything in graphical form starting from formation tops to mud parameters to drilling progress plan for each phase of drilling. In one glance one can have the complete well plan through GTO.

Ref: Quora

Geodetic surveying is the survey in which the curvature of the earth is taken into account and higher degree of accuracy in linear and angular observations is achieved. The geodetic surveys extend over large areas and lines connecting any two points on the surface of the earth are treated as arcs. For calculating their projected distances on the plans or maps, the correction for the earth’s curvature is applied to the measured distances. The angles between the curved lines are treated as spherical angles. A knowledge of spherical trigonometry is necessary for making measurements for the geodetic surveys.

Ref: Quora

Subgrade is the compacted soil that supports all the pavement layers upon it. It is considered as bottom most layer of pavement that bears and transfers all the load of Road to the soil. Highly compacted subgrade ensures long life of Road and wipes out possibilities of settlement.

The success or failure of a pavement is more often dependent upon the underlying subgrade - the material upon which the pavement structure is built. Subgrades be composed of a wide range of materials although some are much better than others. This post discusses a few of the aspects of subgrade materials that make them either desirable or undesirable and the typical tests required to characterize subgrades. A subgrade’s performance generally depends on three of its basic characteristics (all of which are interrelated) as under:

• Load bearing capacity
• Moisture content
• Stabilization with cement or asphaltic binder

Marginally poor subgrade soils may be compensated for by using additional base layers. These layers (usually of crushed stone – either stabilized or un-stabilized) serve to spread pavement loads over a larger subgrade area. This option is rather perilous; when designing pavements for poor subgrades the temptation may be to just design a thicker section with more base material because the thicker section will satisfy most design equations. However, these equations are at least in part empirical and were usually not intended to be used in extreme cases.

A well-planned Road Management system can reduce time and cost of maintenance in an effective way. Here lies the importance of pavement condition survey. It performs a significant role in pavement management. An essential component of PMS is the capability to identify the overall condition of a pavement network and the expected future condition. A PMS addresses the most cost effective maintenance and rehabilitation for each road segment. Ideally, the pavement maintenance would be mostly preventive, so that roads are always in good shape and can provide a smooth and sturdy all - weather traveling surface. That can be beneficial for a wide range vehicle as well as for the users.