Date post: | 31-Oct-2015 |
Category: |
Documents |
Upload: | pabamadhumalie |
View: | 482 times |
Download: | 2 times |
Assignment 1
Report on Visit to Survey Department of Sri Lanka
Table of Contents
1. Geographic Information System Unit.........................................................................................................1
1.1. Introduction..........................................................................................................................................1
1.2. What is GIS..........................................................................................................................................1
1.3. Applications of GIS.............................................................................................................................1
1.4. Advantages of using a GIS..................................................................................................................2
1.5. Use of GIS in Sri Lanka.......................................................................................................................2
1.6. Datum...................................................................................................................................................3
1.7. Layers used in GIS...............................................................................................................................3
1.8. Functions of GIS..................................................................................................................................4
2. Topographical Drawing Unit......................................................................................................................7
2.1. Topographic Drawings.........................................................................................................................7
2.2. Grids.....................................................................................................................................................8
2.3. Sheet Indexing system and Sheet Number...........................................................................................8
2.4. Direction..............................................................................................................................................9
2.5. Map name and Identity........................................................................................................................9
2.6. Topographic maps..............................................................................................................................10
2.7. Topographic Mapping, what is a Topographic Map?........................................................................10
2.8. Thematic map.....................................................................................................................................11
3. The Center for Remote Sensing (CRS).....................................................................................................12
3.1. Satellite Remote Sensing...................................................................................................................12
3.2. Topographic and thematic mapping from satellite image data..........................................................13
3.3. Thematic mapping.............................................................................................................................13
3.4. Main processes in the Center for Remote Sensing............................................................................14
4. Photogrammetric Unit...............................................................................................................................15
4.1. Types of Photogrammetry..................................................................................................................15
4.2. Photogrammetry in Sri Lanka............................................................................................................16
References........................................................................................................................................................18
1. Geographic Information System Unit
1.1. Introduction
The Survey Department is mainly sub-divided into three management units to handle its ‘Central’ functions,
‘De-Centralized’ (provincial) functions and ‘Title Registration’ functions. Geographical Information
Systems (GIS) is under the central function unit. This department’s job is mainly to create and maintain the
GIS used in the Survey Department of Sri Lanka.
1.2. What is GIS
A Geographical Information System (GIS) is an information system that process and handle geospatial data
(data about places on earth) especially with the support of computer systems. The main difference of a GIS
from a normal information system is that GIS can capture, model, store, retrieve, share, manipulate and
present geographically referenced data. As GIS is also an information system it includes the properties of a
normal information system such as collection of users, machines, data, and procedures. GIS can represent
and analyze geographic features and events in digital form.
Purpose of a GIS
The main purpose of having a GIS is that, to solve problems related to topography and/or geography in an
effective and quick manner using geographic data. It assembles, stores and manipulate inputted geographic
data and attribute data. Then it interprets and visualize that data in many different ways (e.g. maps, globes,
reports, and charts) which make it possible to reveal relationships, patterns, and trends about those data.
1.3. Applications of GIS
GIS technology can be integrated into any enterprise information system framework and therefore it benefits
organizations of different magnitudes in almost every industry. Many application areas for GIS have been
identified during the previous decades because of the increasing attentiveness of the financial and strategic
value of it.
Telecommunication and e-Government
Utilities management and Healthcare
Transportation
Disaster and Emergency management
Land administration and Urban planning
Military applications
Environmental monitoring and assessment are some of the application areas of GIS that is identified.
1
Hence, the benefits of GIS is widespread among all those industries and areas mentioned above.
1.4. Advantages of using a GIS
As a result, advantages of a GIS can generally be characterized into five basic categories as follows.
1. Cost Savings and Increased Efficiency
Using GIS has increased the effectiveness and quality of the work. GIS has become very cost effective.
Some ways that GIS reduce expenses are reduction of fuel use, saving staff time, improve customer services
and workflow, enable efficient scheduling, etc.
2. Better Decision Making
GIS is the main technology used by local or international organizations for making better strategic decisions
regarding locations (real estate site selection, route/corridor selection, zoning, planning, evacuation planning,
conservation, natural resource extraction, etc.), which is vital for their success [1].
3. Improved Communication
Since maps are the best way to visualize geospatial data GIS based systems provide high quality maps. It has
become the global language for communicating between different groups of people located in all around the
world.
4. Better Recordkeeping
GIS provides a strong framework for managing geographic accounting records with full transaction support
and reporting tools. E.g. zoning, population census, land ownership, administrative boundaries,
environmental measurements, water flows, and etc.
5. Managing Geographically
The idea is that it is essential for organizations and businesses to be aware and informed about what is
happening in the geographic space in order to forecast and prescribe their future and current actions.
1.5. Use of GIS in Sri Lanka
The Survey Department as the National Surveying and Mapping Organization of Sri Lanka provides the map
data which is the base for any Geographic Information System in the country [2]. Therefore, all other
Government and private organizations use their products and services. For example, Ceylon Electricity
Board, Sri Lanka Water Board, Ministry of Agricultural Development and Agrarian Services, Ministry of
Highways and Road Development, Sri Lankan Army and Forces etc. GIS division has done major
contributions towards the Survey Department since the introduction of ‘digital mapping’ in 1992 by
supporting with its digital topographic vector databases. Some of the major activities of the department 2
currently running under novel developing concepts of the Government are, contributing to Southern Harbor
development project, Southern Airport establishment project, and power generation projects in reserved
regions of the country [3].
1.6. Datum
Datum is a mathematical model of the earth which define the position of the ellipsoid and the origin and
orientation of the coordinate systems relative to the center of the earth. It serves as the reference or base for
calculating the geographic coordinates of a location. Coordinate reference systems are created based on these
datums. Different regions of the earth use different datums that are most suitable for their area. These datums
are called as ‘Local Datums’. It only aligns the spheroid to match that particular region. But there is also a
datum which has its origin is the center of the earth and this datum is called as ‘Geocentric/Earth Centered
Datum’.
There are two types of datums.
Horizontal Datum – used to measure specific position on the earth’s surface such as latitude and
longitude.
Vertical Datum – used to measure the elevations of specific points on the earth or under water depths.
This data is gathered via sea level measurements such as tides, gravity which is measured with geoid,
and ellipsoid models used in horizontal datums.
Datum name: Kandawala
First defined in: 1930
Origin: Fundamental point: Kandawala. Latitude: 7°14'06.838"N, longitude: 79°52'36.670"E
Ellipsoid: Everest 1830 (1937 Adjustment)
Prime Meridian: Greenwich
Kandawala is a geodetic datum for Topographic mapping.
1.7. Layers used in GIS
As mentioned above GIS department uses digital maps since 1992. They have developed over time and
enhanced their databases for 1:10000, 1:250000, 1:50000 map scales. In every map they have represented
separate data in separate layers. This functionality is enable in GIS databases due to the use of computer
systems.
Layers used in 1:50000 map are Building, Transport, Hydrography, Places, Terrain, Administration,
Landuse, and Reserves & Grid.
3
Layers used in 1:25000 map are Road, Boundary, Cities, Contour, Lagoons, Peaks, Railway,
Streams, Tanks, Forests, Village, and Div. sec.
Layers used in 1:10000 map are Building, Transport, Hydrography, Places, Terrain, Administration,
Landuse, Reserves, and Utilities& Grid.
According to different scales each feature is represented in different ways. For example Building layer in
1:50000 map uses ‘Arcs’ to represent a building in a map. But in 1:10000 map Building layer uses ‘Points’
to represent buildings.
1.8. Functions of GIS
GIS branch of survey department has main responsibility over following functions.
1. Data Capturing
2. Data Input
3. Data Storage
4. Data Processing
5. Data Output and Presentation
Data Capturing
GIS branch is not actually dealing with data capturing and they worked with captured data from other
branches such as Remote Sensing and Photogrammetric. But it is a main responsibility of GIS branch to
minimize the error rate of captured data and use them in an accurate manner. So this branch works on data
capturing process as well to bring captured data in to an accurate position.
Survey department uses two basic methods for data capturing.
Aerial Photographs
Data capturing from an aerial photographs has been doing digitally since 1992 that can be directly feed to
any sort of Geographic Information System.
Satellite images
Most of the time large amount of data captured from satellite images and when those images are unclear
officers go for field visits to check the actual land and identify them correctly.
Data Input
Data input covers all aspects of capturing spatial data and converting the data into a form that can be
processed using the computer.
When input data, it is necessary to encode the data and write them to the database.4
There are two aspects of the data that need to be considered separately in geographical information systems.
1. Positional or geographical data necessary to define where the graphic or cartographic features occur-
which means that we need to know the coordinates
2. Associated attributes that record what the cartographic features represent – these are any other relevant
data related to a feature
Data Storage
GIS Branch of Survey Department has a topographic digital data base which consists of 1:50,000 and
1:10,000 scales from existing maps and other sources. This 10K tile (1:10,000) formed by dividing one 50 K
tile (1:50,000) into 25 tiles of 8*5 sq. Km. the total number of tile will be 1834. Each of the tiles consists of
10 layers as coverage. Updating process is very tedious here. The process of edge matching and editing in
coverage is very difficult and time consuming in ArcInfo or ArcEdit environment. Because of the above
difficulties Survey department has been decided to transform existing tile coverage to file geodatabases since
it helps to faster the editing process and checks on quality control process more. Ongoing transform process
of coverage to geodatabases will not reduce existing data fields but new fields can be added.
In present geodatabase is used as the data storage medium in GIS branch since it is the common data storage
and management framework for ArcGIS. Simply, it is a container for spatial and attribute data. The
geodatabase supports all the different types of GIS data that, such as attribute data, geographic features,
satellite and aerial images (raster data), CAD data, surface modeling or 3D data, utility and transportation
network systems and GPS coordinates. Data conversion tools in ArcGIS has suite of easily migrate existing
data into the geodatabase.
Vector data is stored in the geodatabase as thematic layers called feature classes. A feature class is a
collection of geographic features with the same geometry type, such as a point, line, or polygon with their
same attributes; and the same coordinate system. By storing feature classes within a feature dataset,
geospatial relationships can be modeled between the feature classes, enabling more advanced GIS analysis.
Data Processing
GIS branch performs spatial analysis in data processing. Spatial analysis deals with geographic patterns in
data and relationships between features. For example it can give an answer to questions such as, ‘how much
of urbanization has taken place over the years?’ or ‘how much of forest is being destroyed every year?’ and
so on.
Spatial analysis functions are as follows;
Functions Simple database query
5
Arithmetic and logical operations
Complicated model analysis
Database query is used to retrieve attribute data. It can be done by either clicking on the feature or using
conditional statements for complex queries.
Data transformation is done in data processing to remove errors from the data, bring the data up-to-date and
match the data to other data sets. Scale changing, fitting data to new projections, logical retrieval of data and
calculation of areas & perimeters are some examples for data transformations.
Data Output and Presentation
Presenting the information output from a geographical database is a most important function in this branch.
Proper visualization of the results helps in taking decisions for planning of resources. In order to make
decisions on location problems it is important to present the information suitably. This will make it easier to
take correct decisions regarding important geographical factors. Examples are location of schools, hospitals
etc on district population results, location of unstable slopes for stabilizing based on soil and topography
overlays and many more. Their main challenge is to output the results in more understandable manner so
maps, tables and figures (graphs & charts) are used as output methods.
6
2. Topographical Drawing Unit
Topography concern the extraction and representation of surface shape and features of the Earth or other
observable astronomical objects including planets, moons, and asteroids. It will different from ‘fine art' or
‘landscape’ because primarily purpose is to provide a visual record of a particular area rather than as a form
of self-expression. Topography is concerned with mapping common detail in general terms in a precise
measurements and relative location. It will capture the detail such as elevation natural and artificial features.
The graphic representation of the landform on a map by a variety of drawing methods, including contour
lines, hypsometric tints, and relief shading which enable to represent same information in three dimension
model of Earth in abstract manner on two dimension space.
In the process of conversion the abstract representation of actual distance, elevation, relative location and
natural and human made objects will be carried using set of additional detail or features of map. Common
Meta language based on the symbols and standard notations has used in map drawing with the purpose of
common use of general public. The topographic drawing consists of cross-sectional planes, symbols and in
certain number of graphical calculations, based on the purpose.
2.1. Topographic Drawings
Meta data will broadly divide into two called internal and external detail.
Internal Detail
Scale: A map’s scale indicates the relationship between the distances on the map and the actual distances on
Earth. The scale in general will be the scale factor which is indicated as a ratio of distance between the flat
map and the reference globe. For an example survey department of Sri Lanka provide topographic maps in
the scale of 1:50000 and 1:10000.
Symbols: Symbols to represent geographic features which can be natural or manmade or imaginary.
Basically there are three categories called points, lines and area. The using symbol can vary based on the
purpose of map and the scale. Symbols can be scandalized or specific to map. Points can indicate the detail
such as point elevation. The area features, such as vegetation (green), water (blue), and many other distinct
patterns to indicate vegetation, forest etc. Lines that may be straight, curved, solid, dashed, dotted, or in any
combination. The colors of the lines usually indicate similar classes of information like streams, roads etc.
Contours lines are imaginary lines as lines connect points that have equal elevation. If a map shows a large
enough area, contour lines form circles.
7
Sri Lanka survey department has maintained the some standard set of symbols for geographic maps which
are widely used around different institutions in Sri Lanka. The 1:10000 maps will be more descriptive and
having more symbols than the 1:50000 map. Topographical drawing section considers symbols of new map
based on the portability of overlapping. In such situation changing of symbols or merging symbols possible
based on calculations .It make conflicts and confusions to end user.
2.2. Grids
A map will be a projection of a reference of earth which need a unique origin point, standard meridian and
distance measurement schema which enable to derive actual location of map based on system defined in the
map. Sri Lanka currently using Piduruthalagala Mountain as the origin and two datums called Kadawala
datum and Sri Lanka Datum 1999. (Kandawala. Latitude: 7°14'06.838"N, longitude:
79°52'36.670"E.) .Datum is mathematical reference model to actual earth enable to give position based on
geographic coordinate system (longitude and latitudes).
Figure 1: Map Grid Coordinates of 1:10000 Map
The projected map able to resent in Cartesian coordinates .The map usually has two grids based on the
geographic coordinated and the national map-grid coordinates (local). The national map-grid coordinates,
termed SL_GRID_99, are computed using a Transverse Mercator projection. The geographic coordinate
system will represent in longitudes and latitudes while national map-grid coordinates indicated by distance
from the origin added false easting and false northing.
2.3. Sheet Indexing system and Sheet Number
Based on the different purpose different maps can be produce in different scales. Large Scale map which is
more detail will represent in number of sheets under unique indexing covering whole area. It is called as a
map series usually includes a group of similar maps at the same scale and on the same sheet lines or format
designed to cover a particular geographic area.
8
Figure 2: Indicating adjoining Map with Grid North
Under 1:50000 Metric sheet system Sri Lanka has divided in to 92 sections each covering an area 25 km x
40 km and these are divided into 25 1/10,000 sheets, each 5 km x 8 km. Adjoining Sheet numbers ,
Adjoining Sheets Diagram and the map sheet no given to identify the location based on whole Sri Lanka.
2.4. Direction
North on a map is the direction of a line of longitude which converges on the North Pole. A compass needle
points to the magnetic north pole. The magnetic north pole is currently located in the Baffin Island region of
Canada, and from the UK, is west of true north.
The grid lines on national map-grid coordinates define the direction of grid north. The grid lines point to a
Grid North, varying slightly from True North. This variation is smallest along the central meridian (vertical
line) of the map, and greatest at the map edges. The process of projection into the flat surface has caused to
this difference.
2.5. Map name and Identity
Figure 3: Map Name, Sheet Number and Other Detail
Each map will related to the area of Earth which can have references based on the user to identify the
position. Map name describe the purpose of the map, features of map or name of the area based on
administrative boundaries.9
In addition map can include date it is create author, and sources. Other details such as elevation guide,
spheroid, grid and projection note can include if necessary. The data collection for topographic drawing
based on the direct surveying or remote sensing. The selection of which method is based on depends on the
scale and size of the area under study, its accessibility, and the quality of existing surveys.
Maps can be broadly divided into three categories called Topographic maps, and thematic map.
2.6. Topographic maps
Topographic maps are detailed, accurate graphic representations of features that appear on the Earth's
surface. These features include. The topographic map captures major details (features) of earth which are
useful for general purpose and navigation.
Contours are imaginary lines that join points of equal elevation on the surface of the land above or below a
reference surface, such as mean sea level.
Figure 4: Actual Topology represented in 2D maps
2.7. Topographic Mapping, what is a Topographic Map?
Figure 5: Topological Map extraction from 1:50000 Map
The Above map extracted from the 1:50000 map which indicate the tea cultivation of Sri Lanka. It is
possible to inference that sloping areas are highly used for tea cultivation and valleys are used for rice
cultivation
2.8. Thematic map
Thematic map only capture specific geometric data and its attribute highlighting a specific use and theme.
The theme can be social, political, cultural, economic, sociological, agricultural, or any other aspects of a
10
city, state, region, or national. It is contrast to the regular map includes all the detail in brief including
geographical, political and geological and resources.
Understanding Thematic map
Thematic map able to provide inference knowledge of additional detail collected which need to highlight
based on the basic map. The importance of the thematic maps rose due the high level of demand for accurate
maps based on the increase of information.
Figure 6: Thematic Map Based on Jaffna Peninsula
The above map indicates the percentage of families having meal less than three times a day in Jaffna district.
It has taken general gramasewa areas as the primitive unit falling in to the basic map of the administrative
boundaries. The gramasewa areas has given distinct colors based on the legend .Legend differentiated
classes based on the percentage of families having meal less than three times a day.
Later with the evaluation of computer the information storing and extraction improved the new subject area
called Geographic information systems (GIS) which improve the capability to maintain and update the
details of maps. Collection of data from aerial photographs in digitally or digital format manner has been
having to the Survey Department in year 1992.Further manual maps of Survey Department has converted to
digital maps currently he topological drawing section of Survey Department .Topological Drawing section
mainly focus on the updating existing topological maps and generating thematic maps. Topological
Drawing section is capable of producing maps quickly and efficiently using modern technology.
3. The Center for Remote Sensing (CRS)
3.1. Satellite Remote Sensing
Sri Lanka survey department is using this Satellite Remote Sensing technology for their mapping in Sri
Lanka. The Sri Lanka Survey Department has been using Satellite Remote Sensing data for land use land
11
cover mapping with the aerial photographs since 1981. The center for Remote Sensing (CRS) Satellite
Remote Sensing was introduced to Sri Lanka Survey Department in late 1970's. The Sri Lanka Center for
Remote Sensing at the Survey Department act as a central organization for Remote Sensing related activities
in Sri Lanka. The goal of the CRS is to carry out specific operational work related to the Remote Sensing
specially interpretation of aerial photographs and satellite images.[1] The main task of this activity is to
support and supplement the existing mapping and services in Sri Lanka (Land use maps, image maps etc.)
The Center for Remote Sensing in the Survey Department has been using SPOT, LANDSAT MSS & TM,
and IRS Satellite Remote sensing data. It archives the available Satellite remote Sensing data for the country.
Satellite Remote Sensing data has been used for various activities related with earth resources and
environmental activities in cooperation with numerous user organizations. Few examples are Forest Cover
monitoring, paddy land mapping, tea mapping, environmental factors particular influence of chemical and
sediments in Mahaweli River, coastal protection, identification of disease effected plantations.
Present applications in the CRS
Land use mapping
Satellite image mapping
National archiving of satellite data
Figure 7: Satellite Image Coverage in Remote Sensing data at the CRS
Satellite imagery is sometimes supplemented with aerial photography, which has higher resolution, but is
more expensive per square meter. Satellite imagery can be combined with vector or raster data in a GIS
provided that the imagery has been spatially rectified so that it will properly align with other data sets. The
center for remote sensing most of time buys the raw satellite images. Then those images go through
12
processes for mapping purposes. Mainly mapping is done using topographic and thematic mapping from
satellite image data.
3.2. Topographic and thematic mapping from satellite image data
Topographic mapping
The production of topographic maps is based on the restitution of aerial photographs since many decades.
During the restitution process the operator extracts semantic information and geometric information out of
the images.
Though the production of topographic maps from satellite image data is basically very similar, it was
ignored by the cartographic community for a long time. It is of course obvious that the use of satellite remote
sensing for the production and revision of maps is only of interest if the data can be extracted with the
appropriate accuracy, completeness and reliability.
Figure 8: The same landscape in a topographic map and in a satellite image.
3.3. Thematic mapping
Thematic maps generally show geo-referenced data of different types in map formats. Satellite remote
sensing can support thematic mapping in two different ways. In the first place the base map for thematic
mapping can either be a topographic map, which was derived from satellite image data, or directly a satellite
image map. In the second place it is possible to extract the thematic information completely or partly out of
the satellite image data. [2]
3.4. Main processes in the Center for Remote Sensing
1. Convert the raw satellite images in to coordinate system.
13
2. Use reference images, GPS points to geo code. They use Geoview software to geo code.
3. Use Rgis software for digitizing roads, lands, rivers, hydro, buildings, etc in each layer.
4. Use Arcgis software for designing and managing the maps.
The resolution of satellite images varies depending on the instrument used and the altitude of the satellite's
orbit. It is a main factor for creating a better map. High resolution satellite images create better maps. There
are four types of resolution when discussing satellite imagery in remote sensing:
Spatial
Spatial resolution is defined as the pixel size of an image representing the size of the surface area being
measured on the ground, determined by the sensors' instantaneous field of view.
Spectral
Spectral resolution is defined by the wavelength interval size (discreet segment of the Electromagnetic
Spectrum) and number intervals that the sensor is measuring.
Temporal
Temporal resolution is defined by the amount of time (e.g. days) that passes between imagery collection
periods for a given surface location.
Radiometric.
Radiometric resolution is defined as the ability of an imaging system to record many levels of brightness
(contrast for example). [3]
Satellite Imaging Technology (Remote Sensing) has led the way to the development of hyper spectral and
multispectral sensors around the world, a tool that can be used to map specific materials by detecting specific
chemical and material bonds from satellite and airborne sensors. In Sri Lankan point of view the efficacy of
satellite imagery is clear, particularly where the resolution of existing mapping either inadequate or mapping
does not exist. With the availability of high resolution satellite data, therefore, they will greatly contribute to
the field of disaster management in near future.
4. Photogrammetric Unit
Photogrammetry is the technique of determining the geometric properties of objects from photographic
images.3D coordinates of a point, feature or object can be determined by measurements made in two or more
photographs taken from different positions using the principles of triangulation. Most of the time,
14
Photogrammetric surveying uses photographs taken from a special camera in an aircraft. Precise calibration
of the camera, measurement of the position and orientation of the camera, and of the platform in aircraft, is
essential to enable ortho-rectification of the photographs. In the simplest form, the distance between two
points that lie on a plane parallel to the photographic image plane can be determined by measuring their
distance on the image, if the scale (s) of the image is known. This is done by multiplying the measured
distance by 1/s.
The output of photogrammetry is typically a map, drawing, measurement, or a 3D model of some real-world
object or scene. Many of the maps we use today are created with photogrammetry and photographs taken
from aircraft. It is because Photogrammetry is a cost efficient surveying method for mapping large areas. •
Photogrammetry produces electronic terrain models which are hard to produce by other methods.
Photogrammetry may be safer than other surveying methods. It is safer to take photographs of a dangerous
area inaccessible to field crews. Further it creates a photographic record of an instance of a particular subject
area drastically changing.
4.1. Types of Photogrammetry
Photogrammetry can be classified a number of ways but the standard method would be splitting the field
based on camera location during photography. On this basis we have Aerial Photogrammetry, and Close-
Range Photogrammetry.
● Aerial Photogrammetry
● Close-range Photogrammetry
In Aerial Photogrammetry the camera is mounted in an aircraft and is usually pointed vertically towards the
ground. Multiple overlapping photos of the ground are taken as the aircraft flies along a flight path. These
photos are processed in a stereo-plotter (an instrument that lets an operator see two photos at once in a stereo
view). These photos are also used in automated processing for Digital Elevation Model (DEM) creation.
15
Figure 9: Photogrammetry
In Close-range Photogrammetry the camera is close to the subject and is typically hand-held or on a tripod
(but can be on a vehicle too). Usually this type of photogrammetry is non-topographic - that is, the output is
not topographic products like terrain models or topographic maps, but instead drawings, 3D models,
measurements and point clouds. Everyday cameras are used to model and measure buildings, engineering
structures, forensic and accident scenes, mines, earth-works, stock-piles, archaeological artifacts, film sets,
etc. This type of photogrammetry (CRP for short) is also sometimes called Image-Based Modeling.
Figure 10: Close Range Photogrammetry
4.2. Photogrammetry in Sri Lanka
Photogrammetry was familiarized to Sri Lanka through the Survey Department, the National Mapping
Agency of Sri Lanka, which was engaged in map creation by conventional terrestrial methods since its
establishment in 1800. As a responsibility by the nation, the Survey Department was regularly updating and
16
maintaining the maps by similar conventional methods until the middle of the last century. Aerial Survey
Method was first introduced in 1956 for topographical map production work in the department and later, in
1980s, the Satellite Remote Sensing Technique was incorporated through a joint project of Sri Lankan and
Swiss Governments to produce a Land Use Map series. To date, the department remains as the only
photogrammetric agency in the country and the National point for any international contacts for Remote
Sensing.
Before the new system arrives, Sri Lanka was completely air photographed at the scale of 1: 40,000 in 1956
by a foreign agency before the department acquired an aircraft. Later, the departmental aircraft was used for
such programmers carried out to photograph the country at the scales of 1: 10,000, 1: 20,000 and 1: 50,000
at different occasions. For photogrammetric data capturing from photographs, the department the has a few
early models of plotting machines that are now upgraded as semi-analytical plotters with digital encoders,
and two analytical plotters. The output will be the computer generated drawing can increase the accessibility
with GIS. In 1999 department introduced geodetic type GPS receivers to determine ground control points.
Air Survey technology adopted till 1992 was the contemporary practice of analogue photogrammetric
methods. With the change of time these Analogue photogrammetric instruments were raised with digital
encoders in 1992 .Summit Evolution softcopy workstations introduced with Micro stations, which was used
to produce digital topographic data thereafter. Arrangements are now being made to strengthen the process
of data capturing by introducing softcopy photogrammetry. Adequate level of training and knowledge in the
subject area is essential for the production to be start. Further full gear by purchasing of precise scanner,
software, computers and other necessary equipment also needed.
At present, almost all Topographic maps produced by the Survey Department are based on Aerial Surveys.
The photogrammetric department currently involving in updating topological maps of the Northern Province
which are inaccessible due to war in last decades. Large Scale Aerial photographs also provide the accurate
data required for many Cadastral Surveys. Special requirements such as engineering projects as well as for
specialist such as Foresters, Geologists and Urban Planners etc. photogrammetric department capable to
produce thematic maps quickly based on the advancement and expertise gathered.
17
References
[1] http://events.esri.com/uc/QandA/index.cfm?fuseaction=answer&conferenceId=2a8e2713-1422-2418-
7f20bb7c186b5b83&questionId=2441
[2] http://www.nbro.gov.lk/web/images/stories/publications/ls19.pdf
[3]http://www.survey.gov.lk/home/index.php?
option=com_content&view=article&id=59&Itemid=65&lang=en
[4] http://alwie.net/lit/IstMap.pdf
[5] http://en.wikipedia.org/wiki/Satellite_imagery
[6] http://www.survey.gov.lk/home/index.php
[7] http://www.photogrammetry.com/
[8] http://en.wikipedia.org/wiki/Photogrammetry
[9] http://en.wikipedia.org/wiki/Topography
[10] http://us.monografias.com/docs25/topographic-drawings/topographic-drawings.shtml
[11] http://geography.about.com/od/understandmaps/a/thematicmaps.htm
[12] http://egsc.usgs.gov/isb/pubs/booklets/topo/topo.html
[13] www.nbro.gov.lk/web/images/stories/publications
Reference: http://www.dot.ca.gov/hq/row/landsurveys/SurveysManual/13_Surveys.pdf
18