|In Bangladesh data on population
and other socio-economic sectors are collected
by three methods:
- Decennial Population and
- Regular Sample Vital Registration
- Regular Health and Demographic
Post operation evaluations were made on the
outcome of all the three methods. On the 15th
of September 1997 the final dissemination seminar
and expert consultation was held took place
where the experiences of 1991 Population
Housing Census were evaluated and the conceptual
framework for Population and Housing Census
2001 were examined and some recommendations
were made. Two major recommendations of the
seminar were -
- Enumeration area sketch
maps used in the previous censuses must be
upgraded and GIS based Enumeration Area maps
should be prepared so that under enumeration
and duplication remains in control;
- Training procedure
must be improved so that both the content
and the coverage error can be reduced to tolerable
Keeping these recommendations into considerations
new technologies were scratched and linked to
the following aspects for discussion in the
first group meeting of the working party:
- Use of GPS in GIS based
Enumeration Area Map Making; and
- Use of Multi-media Technology
in PC based Data Collection Training.
Use of GPS in GIS based Enumeration area Map Making
||Maps and geo-codes are two very important input
tools to modern censuses surveys and vital registration
activities. In the past enumeration area (EA)
maps used in the census were sketch maps. It has
been noticed that inaccuracies and incompleteness
of maps have direct impact on the coverage and
quality of the census and survey results. In view
of the circumstances GIS technology were tested
to produce EA maps from both the spot imageries
and the Areal Photographs for a district. It was
observed it is feasible to prepare revenue
village (Mauza) based EA maps if time and resources
are provided and co-ordinated efforts are made.
Currently in Bangladesh there are 19 organisations
who are directly involved in GIS based map making.
Out of them six organisations have acquired the
GIS technology and have map coverage for 494 sub-districts
and 64 districts :
- Bangladesh Resource
and Remote Sensing Organisation (SPARRSO);
- Local Government Engineering
- Environmental and GIS
Support Project for Water Sector Planning
- National Data Bank
- Social Resource Development
- Bangladesh Agricultural
Research Council (BARC)
||Categorically these organizations are well equipped
with the software's like Arc/Info, Areview, ERDAS,
||Gobal Positioning System
||Gobal Positioning System (GPS) is a satellite
based system which can be used in land surveying.
The word GPS is high sounding but its application
is useful and cost effective specially for hilly
areas, forest areas, desert areas etc. It can
achieve accuracy upto 100 meter horizontal, 156
meter vertical and 340 nano-seconds in time dimensions.
For civil users standard positioning system (SPS)
is charge free and can be used as back-up. GPS
uses receivers for navigation, positioning, time
dimension and other research. It operational aspects
have been explained in the concepts - in chapter-4.
||The carrier phase tracking is the important
phase of GPS which had brought resolution in land
surveying. A position can be measured upto 30
km from the reference point without intermediate
points. The use of GPS requires specially equipped
carrier tracking receivers.
||Differential GPS is a better addition to the
GPS system, Special software is required to process
carrier phase differential measurement. Newer
technique such as Real-Time Kinematics (RTK) processing
alowed for centimeter relative positioning with
a moving remote receiver.
||Softwares available in the market are -
- The geographic calculator
- The geographic tracked
- The geographic transformer
- Geolink(r) (GPS/GIS Field
- DNAV-212 (Field data collection
- Fieldworker (TM 2.3) pen-based
data collection system
||System requirements :
Windows (TM 3.0 95/98 )
PC Compatible 486 or higher
Math coprocessor recommended.
||Geolink(r) Mapping System
||The Geolink mapping system is a fully integrated,
flexible GPS/GIS field mapping and vehicle tracking
system specially designed to provide users with
the industry's most cost effective and powerful
GPS/GIS mapping tools available. The geolink code
module serves as the host license and provides
all basic data collection, editings GIS translation
and data quality assurance function.
||GPS Techniques and Project
- Small civil GPS receiver
unit cost = US$ 200 - 2000/-
- Receiver in DGPS unit cost
= US$ 5000& - $ 40000/-
Use of multimedia in PC based Data Collection
In all the post census, survey
and vital registration evaluation reports the
expert opinion was that improvement of standard
and level of training is a must for improving
the quality of population data specially the
age data, Census is a big operation. For census
as well as for big survey operation large number
of master trainers are required. It was very
difficult to have expert trainer in the regular
setup of the institution concerned. As a result
of which the quality of information suffer.
Technology is now available to bring the multimedia
and PC computer as an aid to effective training
as well as a substitute of efficient trainers.
CBT requires methodical instruction design
approach. The course design should have
"Electronic page turner", "Hypertext", "Graphics",
"Audio" and "Video" and constant interaction
facilities in CBT. It software should be easy
to handle. There should multiple questions and
answers script which should be exercised by
the trainers. CBT can be used as an aid. It
can also be used as distributed training
without the full time attendance of an instructor.
CBT has the benefit of reduced travel cost,
less time off the job, shared training and implied
standard and uniformity in training.
A computer software program is to developed
as a "Courseware" by the expert which will be
the learning vehicle. The software will be complete
with lesson content, questions, branching logic
Software like Audio Applications, Multimedia
Media Studio VE 2.5, Coral photo-paint Photoshop,
Powerpoint, HTML, Harvard Graphics, Microsoft
Frontpage etc can be used as the software for
It is believed that in the coming
few years PC computers will be more user friendly
and web page technology video conferencing and
satellite facilities will be available at low
cost. We are now in the transition period of
two censuses. So we can explore the possibility
of using GPS in GIS based map making. It is
also high time to use multimedia and hypertext
facilities in PC based training.
Concepts of key terms of GPS
||Global Positioning System
||5.1.1 Space segment
Space segment of the system consist of 24 GPS
Satellites 21 Navigational space vehicle (SV)
and 3 active spares orbit the earth in 12 hour
orbits. These orbits repeat the same ground track
(as the earth turns beneath them) once each day
. The orbit altitude is such that the satellite
repeat the same track and configuration over any
point approximately each 24 hours (4 minutes earlier
||5.1.2 Control Segment
The control segment consists of a system of tracking
stations located around the world.
||GPS Master control and Monitor Network
The Master control facility is located at Falcon
Air Force Base in Colorado. These Monitor Stations
measure signals from the SVs which are incorporated
into orbital models for each satellites. The models
computes orbital data and SV clock corrections
for each satellite. The master control stations
uploads orbital data and clock data to the SVs.
The SVs then subsets the orbital data to GPS receivers
over radio signals.
||5.1.3 User Segment
The GPS user segment consists of the GPS receivers
and the user community. GPS receives convert SV
signals into position, velocity and time estimates.
Four satellites are required to compute the four
dimensions of X, Y, Z (position) and Time.
GPS receivers are used for navigation, positioning,
time dimension and other research.
||Navigation in three dimension is the primary
function of GPS. Navigation receivers are made
for aircraft, ships , ground vehicles
and for hand carrying by individuals.
- Precise positioning is possible
using GPS receivers at reference locations
providing corrections and relative positioning
data for remote receivers . Surveying, geodetic
control etc are examples.
- Time and frequency dimension,
based on the precise clocks on board the SVs
and controlled by the monitor stations is
another use for GPS.
- Research projects have
used GPS signals to measure atmospherise
||Standard Positioning System
||Civil users worldwide use the standard positioning
system (SPS) without charge or restrictions. Most
receivers are capable of receiving and using the
SPS signal. The SPS accuracy is intentionally
degraded by the use of selective availability.
||SPS Predicable Accuracy
- 100 meter horizontal accuracy
- meter vertical accuracy
- nano second time accuracy
||The GPS accuracy figures are 95% accurate and
express the value of 2 standard deviations of
radial error from the actual antenna.
||GPS Satellite Signals
||The SVs transmit two microwave carrier signals
. The L1 frequency (1572.42 MHz) carries the navigation
message and the SPS code signals. The L2 frequency
( 1227.60 MHz ) is used to measure the inospheric
delay by PPS equipped receivers. Three binary
codes ( C/A Code, P-code and L1-C/A codes) shift
the L1 and / or L2 carrier phase.
||The GPS navigation message consists of time
tagged data bits marking the time of transmission
of each sub-frames at the time they are transmitted
by the SV. A data bit frame consists of 1500 bits
divided into five 300 bit subframes. A data frame
is transmitted every thirty seconds. Three six-
second subframes contain orbital and clock data.
SV clock corrections are sent in subframe one
and precise SV orbital data for transmitting SV
are sent in subframes two and three. Subframes
four and five are used to transmit different pages
of system data. An entire set of twenty-five frames
(125 subframes) make up the complete navigation
message that is sent over a 12.5 minute period.
||Position and Time from
||5.5.1 Code phase
The GPS receiver produces replicas of the C/A
and or P(y)-code. Each PRN code is a noise. The
receiver produces the C/A code sequence for a
specific SV with some form of a C/A code
generator. Modern receivers usually store a complete
set of precomputed C/A code chips is memory but
a hardware, shift register, implementation can
also be used.
||5.5.2 Pseudo -Range
The position of the receiver is where the pseudo-ranges
from a set of SVs intersect.
||5.5.3 Receiver position,
Velocity and Time
Position in XYZ is converted within the receiver
to geodetic latitude, longitude and height above
- Geodetic coordinates;
- ECEF XYZ conversion to
- Geodetic to ECEF XYZ.
||Carrier phase Tracking
- Carrier phase tracking of
GPS signals has resulted in a revolution in
land surveying. A line of sight along the
ground is no longer necessary for precise
positioning. Positions can be measured upto
30 km from the reference point without intermediate
points. The use of GPS requires specially
equipped carrier tracking receivers.
- L1 and/or L2 carrier signals
are used in carrier phase surveying L1 carrier
cycles have a wavelength of 19 centimenters.
If tracked and measured these carrier signals
can provide ranging measurements with relative
accuracies of millimeters under special circumstances.
- Tracking carrier phase
signals provides no time of transmission information.
- Carrier phase is tracked
at both receivers and the changes in tracked
phase are recorded over time in both receivers.
||GPS Error Sources
||GPS errors are combination of noise, bias, blunders.
||Differential code GPS (Navigation)
||Differential corrections may be used in real
time or later with post processing technique.
- Real-time corrections can
be transmitted by radio link
- Corrections can be recorded
for post processing
||Differential Carrier GPS
- All carrier phase tracking
is differential, requiring both a reference
and remote receiver tracking carrier phases
at the same time.
- In order to correctly estimate
the number of carrier wavelengths at the reference
and remote receivers they must be close enough
to ensure that the Ionospheric delay difference
is less than a carrier wavelength.
- Special software is required
to process carrier phase differential measurements.
Newer techniques such as Real-Time Kinematics
(RTK) processing allow for centimeter relative
positioning with a moving remote receiver.
||Trimble Navigatiion publishes
two booklets on GPS which I found to be useful
references in preparing this document:
||GPS - A guide to the Next
Utility Differential GPS Explained
645 North Mary Avenue
Post office Box 3642
Sunnyvale, CA 94088-3642
Phone 1-800-827-8000 or 408-481-8000
Smith, JR, 1988, Landmark Enterprises,
Cordova ISBN 0-910845-33-6. Check your Library.
||Guide to GPS Positioning
prepared under the direction of David Wells
May be ordered from :
Canadian Institute of Surveying
Box 5378, Station F
Ottawa, Ont. Canada K2C 3J1
||Internet sites : GPS based
||a) mirrored at:
||NMEA-0183 interfacing info files and programs
(and this FAO, an NMEA-0183 FAQ, and a Garmin
The US Coast Gaurd's Navigation Information web
Stie - the official source for civilian GPS information.
University of New Brunswick Dept. of Geodesy and
Misc GPS data and Garmin FAQ
Look for the links:
Amateur Packet REporting System (APRS) (current
The latest release of MacGPS, version 0.3dl.
Coordinational Scientific Information Center(CSIC)
Russian Space Forces (GLONASS)
MIT Lincoln Lab GLONASS homepage.
Marine DGPS beacon information
DCI (Differential Corrections Inc) home page -
DCI is a commercial DGPS provider
Info on UTMS
Details about UTM and Grid Zone Designation points.
Introduction to GPS navigation
International GPS Service for Geodynamics (IGS)
High-accuracy scientific uses of GPS
||Internet sites : PC based
||PC - Based Training Library
PC- Based Training Library. Training modules are
listed below. Each module can be downloaded to
your PC. We recommend that each module be downloaded
to a . Http://www.
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