Geospatial services

2D Feature mapping from High Resolution Satellite images

Remote sensing is a vital system to acquire information of earth resources and environment. Remotely sensed images comprise of spectral, spatial and temporal resolution. The introduction of High-resolution satellite imagery is projected to reduce cost for medium and small scale topographic mapping. Since high-resolution satellite imagery has a much close-fitting field angle, the projection of images is nearly calculated by parallel rather than central systems. Using high resolution we can extract valuable information that will serve as a reference to bigger data needs and planning.

The feature extraction stage is intended to obtain a solid, non-redundant and evocative demonstration of observations. It is accomplished by removing repetitive and irrelevant material from the data.

satimageinterpretation

satimageinterpretation


SBL has perfected its capabilities in 2D feature mapping in the form of base mapping, land use land cover mapping and other types of thematic mapping. This kind of remote sensing services requires the knowledge of pre-processing on the satellite images. These pre-processing steps includes geo-referencing for geometric corrections and image enhancement for radiometric corrections. Digitally enhanced and geo-referenced images can be (re)projected to real world co-ordinate systems to put it in use for 2D feature extraction.
map digitisation

map digitisation

GIS data represents real world entities and features such as roads, land use, elevation, trees, waterways, etc. In GIS all features are grouped under the classes of point, line or polygons. Points are the smallest entity in GIS. Land marks, spot heights and point features such as locations of wells, ATM’s etc. can be represented in the form of points. Lines constitute a series of points called vertices and nodes with a start point and an end node point. Transportation network, drainage network, telecommunication lines, power transmission lines, sewerage network and other utility and transport networks can be represented in the form of lines. Polygons are closed features in which a line has start point and end point the same and which will encompass an area within it. Parks, water bodies, residential areas and forests can be represented in the form of polygons.

For 2D feature extraction services SBL will follow a classification schema derived after the requirement and need study established with the end-client. For example, for a forest department forest land parcels along with hydrographic and transportation network will be captured. For a mining firm during their replacement and rehabilitation process residential buildings, plantations, and orchards may be the main concentration. The thematic mapping using 2D features will be established as per the project and need requirements and is designed with a long term vision of serving the future changes and developments.

GIS mapping for 2D features extraction can be possible through aerial photographs as well. The features can be extracted using image interpretation keys such as tone texture, size, shape, association ext. SBL’s experienced image interpreters will deduce the images to useful thematic categories based on the classification schema. The final stage of the GIS based mapping services is the cartographic layout preparation. Each and every mapped 2D features will be given with a suitable standard symbology and layout can be prepared based on standard cartographic norms. The above notes explains in general the 2D mapping approach adapted by SBL.

SBL UK to partner with Ordnance Survey at major construction event.

uk-event
SBL’s UK division is delighted to have been selected by Ordnance Survey – the UK’s National Mapping Agency – as an exhibitor Partner on their stand at Digital Construction Week in London. In conjunction with IDC, we will be showcasing how Ordnance Survey map data products can be maximised through innovation.

The event takes place between 20th and 22nd October. Please feel free to visit us at the OS stand – M42 – for a demonstration.

We will issue a more detailed communication closer to the event. In the meantime further information can be found here:

http://www.digitalconstructionweek.com/home

Use of Airborne LIDAR in Transmission Line Projects

The growing energy demand is an issue that power utility authorities incessantly face. The creation of new transmission lines is not always probable due to complications in acquiring rights-of-way and obtaining environmental approvals. Airborne LIDAR uses a precise laser scanning technology that offers decidedly accurate terrain and tower elevation data for the transmission line corridor. The advanced software tools allow the analysis of critical distances, obstacles identification, slackness calculation, catenary shape calculation, and location of structures besides allowing data to be exported to specialized engineering softwares.
GIS plays an important role regarding operation planning, data maintenance and design of transmission lines. A great amount of data is required for the operation and maintenance of data related to transmission lines, which includes property ownership data, corridor land use/land cover (LULC), transmission line situation and characteristics. The physical features of the lines and corridor LULC are determined during construction but has to be updated due to the constant change in surroundings during the lifetime. Automation of technological procedures involved in data collection, integration and processing will ensure increased efficiency in the management of the utilities. Dispensation of the data discusses to the production of complete topographic GIS products including their custom-made presentation and analysis.
LIDAR (Light Detection and Ranging) is a contemporary remote sensing technique for the collection of high density and accurate topographic data, which allows high-speed and economical data acquisition of power utility networks. LIDAR together with GIS technology offers efficient tools for database management and analysis.

Fig 1. LIDAR components

Fig 1. LIDAR components

Further to range measurements, some LiDAR systems are also adept in registering the intensity of the backscattered laser pulse. Intensity is defined as the ratio of strength of reflected laser to that of emitted laser, and is influenced mainly by the reflectance of the reflecting object (Song, 2002). Reflectance deviates with material characteristics so that different materials have different reflectance. Therefore intensity images may be supplementary information for a LULC classification. The merging of intensity images with Elevation information produces an image where features can be easily identified. Intrinsic to the collection process the above mentioned images are ortho-rectified images facilitating in the collection of required data for a GIS System. These ortho-images can be used as location image references to maintain or to update an existing GIS database.

111
Figure 2 – (a) Intensity Image (b) Image obtained by fusing intensity information with elevation information.

Results of the managed LIDAR data consists of 3D information about cables, structures as well as all hindrances along the corridor in a form of a point cloud with X, Y, Z coordinates and intensity value. Post-processing actions are needed in order to classify features and to develop additional information. Ground and cable points are categorized using algorithms available in TerraScan software.

Picture4

Among the non-ground points power lines strings can be captured using top views and need to ensure that it connects all the towers. This classification is the result of analysis by an automated filter developed which detects all LIDAR hits returns from the power lines and can be categorized as wires. Towers were also can be detected in a similar way. Critical points can be detected along the transmission lines and exact height needs to be assigned to each object. 50m either side of the transmission lines can be considered for object search and exact height of the objects can be derived. The objects encountered will be houses and vegetation in general. A vegetation clearance report will help to details location of the critical points and its complete information.
LIDAR technology provides a well-organized collection of high density and accurate topographic data, being one of the most recognized cost-effective and high-speed method to such projects. Above and beyond the obstacles and vegetation along the corridor, the location and height of the prevailing towers can be derived precisely. The high density of the laser points enables accurate delineation of the cables as well as the derivation of the connection points. LIDAR in concurrence with GIS methodologies provides efficient database updating and analysis.

3D feature extraction services

3D shapes have been functional in many fields, such as 3D City modelling, Terrain Visualization, industrial design, education, animation entertainment and preservation of historical sites, etc. Feature extraction of 3D shapes is an important branch of Geographical Information Systems using the advanced technologies like Digital Photogrammetry, LiDAR Data processing and pattern recognition, attracting more responsiveness from many technocrats. 2D feature mapping shows only horizontal features on a planar surface, without elevation contours to depict the terrain, whereas in 3D topographic mapping contour and elevations are vital parts. More importantly combination of Planimetric/Topographic Mapping is a depiction of the Earth surface features in 3D means and used for geospatial analysis and modeling.

Picture1(1)

SBL’s 2D/3D Feature Extraction in-house expertise qualifies us to capture data from small to large scale stereo models and generate high precision digital topographic maps. SBL 3D feature extraction services provides accurate digital planimetric feature extraction for cartography mapping and 3D topo mapping by extracting surface features like railroads, buildings, hydrological features, vegetation, etc., with proper coding and symbology.
     Viewing the features extracted from the above methods and get superimposed on the 3-dimensional digital aerial photograph, ensures that editing and collection time is accurate and complete.
SBL’s ability to create customized databases and cartographic map representations is useful in meeting any specification or software format.

Picture2

The benefit of 3D features is the value-added geospatial information that can be derived from high resolution stereo images and hi-density point cloud data. This comprises three specific data products, not exclusively, Digital Orthophoto, digital terrain models and 3D vector data. Digital Orthophoto have turn out to be a standard constituent of base map data, and can be used for accuracy assessment, 2D vector digitizing and update, change detection and a number of other applications. 

AREAS INFLUENCED BY 3D APPLICATIONS:
     •Long Range Planning
     •BIM 
     •Utility Network Designing
     •Plant/Facility Planning & Management
     •Roadway Design
     •Utility Management
     •Landfill/Quarry Management
     •Topographic Surveys
     •Volumetric/Quantity Calculations

Parcel mapping through GIS technique

New Image

A digital record of land parcels or plots is a necessity of modern day administration of any country. In general these data is available in old paper maps and cloth mounted maps which are poorly maintained. In modern era, with every aspect of life is going digital, it is imperative to get the parcel/plot boundaries also in digital form for effective administration and as part of the e-governance initiatives. Land administration will be much easier with parcel boundaries in digital parcel map or Cadastral map. The Cadastral map is one of the basic registers that administration at village, town, city and country can have.

SBL Geospatial Services division is having in-house experience and expertise in executing such GIS services. Geographic Information System (GIS) is an appropriate tool used in mapping parcel boundaries. First step in such mapping process is geo-referencing of the parcel maps after converting the paper maps into raster format by scanning method. The ground control points required to register scanned images to the ground is possible through field surveying, from other georeferenced maps, from open source data. Geo-referenced parcel map can be used digitize the parcel boundaries through heads-up digitization. The mapped objects can be point, line or polygon. Added advantage of parcel mapping in this way is that, one can incorporate any number of attributes to the digitized parcel boundaries. This will explicitly give ownership details, history of ownership, change details of the properties and any other relevant information deemed fit for the purpose.

New Image2

The digital parcel map is the vital component of any cadastral system and is used for legal, administrative and economic decision making and an irrefutable input for planning and development. One of the most important and basic benefit is that individuals can easily come to know about the area of land under their ownership and other details of their own property. This will help government directly by getting right amount of tax without any evasion due to poor record maintenance and difficult retrieval process of the same. It will greatly help urban development departments by assessing accurately parcels and properties affected by any developmental program and decision making will be much easier as we know the impact beforehand. Municipality planning will also be much easier with a digital parcel map, as the department is having accurate details of properties under its jurisdiction.

Most suitable GIS software, ArcGIS is nominated for carrying out the parcel mapping work. Besides digitizing, attribute assignment and management and geo database management, topology building and checks will be very easy in this software platform. Parcel mapping services also include mosaicking or seamless joining of adjacent maps so that village, taluk or district level data can be viewed and analyzed simultaneously. This will be highly helpful for the decision makers. Unlike paper maps and cloth mounted maps, digital parcel will be easy to analyze for area calculations and other statistics. The final results of the parcel maps can be represented in the form of ready to print maps by applying cartography techniques to the mapping process. Standard mapping symbology can be used to demote boundaries of parcels and other details thus mapped.

The paper or cloth parcel map was observed as a static, plain view of preselected areas, available at fixed scales, but due to the advances of the geospatial technology, it is now progressing into a dynamic, recurrently updated network of interconnected databases with large amounts of geographically referenced information linked to a comprehensive central digital parcel database.

GIS for Utility Mapping

Utilities intrinsically are laid out geographically over a large areas of a city, state or country. It’s a demanding task to organize the information, develop and maintain the concomitant assets and infrastructure which are in a form of connected networks. GIS technology supports in making more intelligible databases of the network by placing the assets accurately on Maps and thus making it easier to identify and manage with ground truth visibility.
SBL provides utility mapping services in the following domains:

  • Electric Power Lines
  • Telecommunication Networking
  • Oil and Gas
  • Municipal Utilities
    • Waste Water
    • Storm water
    • Water supply lines
  • Traffic Utilities
  • Railway Utility Mapping

utilitty-mapping

SBL Geospatial Services has been in the forefront of assisting national and international clients with their specific utility and asset mapping. SBL possess in-house capability to understand, map and analyze any kid of utility mapping requirements. The multi-technology approach that SBL uses in their utility mapping services, by the means of LiDAR mapping, Aerial and UAV photography, Satellite imagery and paper to CAD conversion, has helped large private and government organizations in tuning their decision support and making systems to be robust, accurate and responsive.

GIS utility mapping services offers a collective platform to access data, manage assets, update utility network information, incorporate work orders, find customer information, and prepare reports.

Accurate and precise network mapping is well-thought-out to be a vital aid in building, planning, refurbishing and maintaining all consumers and assets of a Utility. The GIS datasets gets cohesive with all proven modeling software tools, ERP and MIS applications, SCADA systems, thus encompassing the usage of GIS technology further than just mapping.

LiDAR DATA PROCESSING AND ASSET MANAGEMENT

LiDAR(Light Detection And Ranging):A form of representation of 3D surfaces, Point cloud data, are usually produced by aerial or terrestrial laser scanning, also known as Light Detection and Ranging (LiDAR). The data is produced as sets of very dense (x, y, z) points or in a more common, binary format called LAS that may include values of multiple returns and point intensities. Many leading GIS processing software’s now accommodate and supports basic and advanced LiDAR data processing and analysis. LiDAR is emerging as one of the cost-effective and accurate data capture system to manage large assets such as Railway stations and other public/private infrastructures.
SBL GIS Services division has been in the forefront of processing LiDAR services for some time now. Our LiDAR data processing services has been entrusted with prestigious and complex Infrastructure modelling projects across many geographies. One such example is demonstrated in the picture given below.

Picture1
Fig-1: All visible data captured as vector data with the help of Terrestrial LiDAR scanner point cloud data related to this project and attributed to their respective code. The above view is illustration of the output.

The Science behind LiDAR Working
LiDAR working is quite simple and it works on the principle of Light – speed and time taken to reflect the same from a surface. The distance is calculated from the difference between the time when a beam of light hits a surface and measure the time it takes to return to its source. Light travels very fast – about 300,000 kilometers per second, or 0.3 meters per nanosecond so we feel the instantaneous result when a light is turned on. The paraphernalia required to measure this needs to function extremely fast. Only with the advancements in modern computing technology has this has become possible.
Distance = (Speed of Light x Time of Flight) / 2

USES OF LiDAR MAPPING.
One of the main focus of LiDAR services in the Urban Infrastructure Mapping.

Urban Infrastructure Planning  
Urban Planning or City development is the science of land use planning which considers several aspects of the as-built data and social environments of the area of interest. LiDAR Mapping is a moderately new technology for obtaining Digital Surface Models (DSMs) and Digital Building Models. This data, when combined with orthorectified images, can create highly detailed Surface Models and eventually 3D City Models.
Wayside assets include tarmacs, streetlights, signs, advertisement boards, traffic signals and street furniture. A thorough understanding of all the assets, what they are and where each asset is located, is crucial to the development of an asset portfolio.
An accurate record of all assets along the transportation network is vital to asset management, to plan a maintenance schedule and budget costs. A bigger challenge than developing the asset database is keeping it up to date and this is where the cost-effective, accurate LiDAR Mapping will come into play.

UAV DATA PROCESSING FIELDS OF APPLICATION

UAV data processing

UAV data processing


This write-up intends to present birds eye view of fully automated and accurate mapping solutions based on ultra-light UAV imagery. We showcase interesting observations in the field of UAV mapping, the steps to analyze the accuracy of the automated processing on several datasets. The software used to process is one of the leading and evolving software in the UAV data processing domain.
The accuracy highly depends on the ground resolution (GSD) of the input imagery. When chosen appropriately this mapping solution can compete with traditional mapping solutions that capture fewer high-resolution images from airplanes and that rely on highly accurate orientation and positioning sensors on board. Due to the advancement of computing practices and processing prowess of computers and careful integration with recent computer vision techniques, the result is robust and fully automatic and can deal with inaccurate position and orientation information which are typically problematic with traditional techniques.
SBL’s geospatial team is one of the first in the region to process such images. Processing of UAV images has its own challenges. SBL used to receive post-processed UAV images along with IMU and GCPs as input. Aerial Triangulation is the first step performed. During this stage Ground Control Point (GCP) and Actual Check Point (ACP) reports has been generated. This is an iterative step till we get desired accuracy. The following will explain in brief some of the critical steps in the processing of UAV data.

  1. The software examines for matching points by analyzing all images. The software used here an improved version of the binary descriptors, which are very powerful to match image points quickly and accurately.
  2. Those matching points as well as estimated values of the image position and orientation provided by the UAV autopilot are used in a bundle block adjustment to reconstruct the exact position and orientation of the camera for every acquired image.
  3. Based on this re-establishment the matching points are corroborated and their 3D coordinates calculated. The geo-reference system is WGS84, in this case, based on GPS measurements from the UAV autopilot during the flight.
  4. Those 3D points are interpolated to form a triangulated irregular network in order to obtain a DEM. At this stage, construction of a dense 3D model increases the spatial resolution of the triangulated data.
  5. This DEM is used to project every image pixel and to calculate the geo-referenced ortho-mosaic. The ortho image will be devoid of positional and terrain displacement inaccuracies.
  6. Picture1
    One of the major application for which UAV images used are for agriculture. UAV images are ideal for small size farms. Plant counts such as corn counting will give an idea of yield from those plants. Plant health monitoring, differentiating species of agricultural farms/plants and plantation estimation are the major task performed for agriculture. Growth stages of the farms can also be monitored using ortho images acquired through UAV process. UAV image processing is also helpful for the site selection for solar farms.
    In case of forestry, UAV images are very helpful in species identification. SBL’s interpreters have identified forest species and enabled the client to map forest land parcels. It is a tool to monitor de-forestation as well as afforestation. Golf courses are another field where UAV data sets are highly useful. Golf course features can be mapped with their actual heights through this process.
    Mining industry is the most benefitted in the usage of UAV technological advancement. As most of the mines are spread over small areas, UAV data acquiring and processing is very cost effective. Along with other data processing, SBL has got the expertise in generating contours and mining related features to very minute levels of detail.

Photogrammetry and Remote sensing

SBL is in the fore front of using the latest of mapping technologies such as Photogrammetry and Remote sensing to cater to the GIS services demands in the world-wide industry. As a leading GIS Services provider SBL has executed several complex Aerial Photogrammetry projects towards the fulfilment of Photogrammetry mapping demands.

The following is a brief introduction to Photogrammetry and Remote Sensing for those who are new with the technology.

BLOG-IMAGE

Photogrammetry

Photogrammetry, as its name implies, is a 3-dimensional coordinate measuring technique that uses photographs as the fundamental medium for metrology (or measurement). The fundamental principle used by Photogrammetry is triangulation or more specifically called Aerial Triangulation. By taking photographs from at least two different locations, so-called “lines of sight” can be developed from each camera to points on the object. These lines of sight (sometimes called rays owing to their optical nature) are mathematically intersected to produce the 3-dimensional coordinates of the points of interest.
The expression Photogrammetry was first used by the Prussian architect Albrecht Meydenbauer in 1867 who fashioned some of the earliest topographic maps and elevation drawings. Photogrammetry services in topographic mapping is well established but in recent years the technique has been widely applied in the fields of architecture, industry, engineering, forensic, underwater, medicine, geology and many others for the production of precise 3D data.
Branches of photogrammetry

There are two broad based branches in Photogrammetry

  • Metric Photogrammetry : Deals with the precise measurements and computations on photographs regarding the size, shape, and position of photographic features and/or obtaining other information such as relative locations (coordinates) of features, areas, volumes, These photographs are taken using a metric camera and  is mostly used in the engineering fields e.g. surveying etc
  • Interpretive Photogrammetry: Deals with recognition and identification of the photographic features on a photograph such as shape, size, shadow, pattern etc to add value and intelligence to information seen on the photograph (annotation).,

Remote Sensing

Remote Sensing is a closely aligned technology to Photogrammetry in that it also collects information from imagery. The term is derived from the fact that information about objects and features is collected without coming into contact with them. Where remote sensing differs from Photogrammetry is in the type of information collected, which tends to be based on differences in color, so land use and land cover is one of the primary output of remote sensing processing. Remote sensing was originally conceptualized to exploit the large number of color bands in satellite imagery to create 2D data primarily for GIS. Nowadays remote sensing tools are used with all types of imagery to assist in 2D data collection and derivation, such as slope. Software tools today tend to hold a much wider range of image technologies such as image mosaicing, 3D visualisation, GIS, radar as well as softcopy Photogrammetry.

Key concepts:

  • Spatial resolution.
  • Radiometric resolution. 
  • Spectral resolution. 
  • Temporal resolution
    • Spatial resolution describes the ability of a sensor to identify the smallest size detail of a pattern on an image. In other words, the distance between distinguishable patterns or objects in an image that can be separated from each other and is often expressed in meters.
    • Spectral resolution is the sensitivity of a sensor to respond to a specific frequency range (mostly for satellite and airborne sensors). The frequency ranges covered often include not only visible light but also non-visible light and electromagnetic radiation. Objects on the ground can be identified by the different wavelengths reflected (interpreted as different colours) but the sensor used must be able to detect these wavelengths in order to see these features.
    • Radiometric resolution is often called contrast. It describes the ability of the sensor to measure the signal strength (acoustic reflectance) or brightness of objects. The more sensitive a sensor is to the reflectance of an object as compared to its surroundings, the smaller an object that can be detected and identified.
    • Temporal resolution depends on several factors–how long it takes for a satellite to return to (approximately) the same location in space, the swath of the sensor (related to its ‘footprint’), and whether or not the sensor can be directed off-nadir. This is more formally known as the ‘revisit period’