Articles in the Geodesy Category

Dec 2005 | Comments Off on Geodetic commentary
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The Mix up of “X, Y, Z” Coordinates Between Photogrammetry and Geodesy
In Spatial considerations –
In geodesy, the “ZXY” coordinate system is “right-handed”, where the right thumb points towards the Z-axis, index finger towards the intersection of the Reference Meridian and Equatorial planes, and middle ?nger or the positive Y-axes, which is …

Dec 2005 | Comments Off on Geodetic Misunderstanding

1. Spheroid is considered equivalent to an ellipsoid.
2. The longitude at the North or South Pole is zero degree.
3. The Mean Sea Level (MSL), a time-variant “average”, is
considered as time-invariant and time-independent.
4. The measured “dn” along a spirit level loop sum up to zero.
5. Imagine a freely ?owing ocean or sea channel under
a continent and it represents the Geoid.
6. The geoidal undulation or height (N) is equivalent to orthometric height (H).
7. There are “yours” and “mine” geoids. In other words every country has its
own geoid, creating a “political” boundary value problem for gravity.
8. When one has to re-observe at any station, it does not make any
difference so long one is observing within “few” meters.
9. If one asks for and gets a height as “123.4 m”. It is OK to add
zeros at the end, e.g., 123.4000, to make it more accurate.

Nov 2005 | Comments Off on Signal propagation through the troposphere
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Space environmental effects on satellite communication can be considered as related to space segment, ground segment and on the signals propagating through the earth’s lower and upper atmosphere. The atmospheric structure has significant influence on signal propagation. This has definite influence on the data processing methodologies. The specific applications with which are concerned here are …

Oct 2005 | Comments Off on CLASSROOM GEODESY
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The Coordinates Class room espouse readers to graticules of Mathematics and Physics that epitomize the Geospatial Information Technology. A chain of structured presentations related to interdisciplinary principles that define Geodesy, GPS, GIS, Geospatial data management and Image processing are to be en suite in this section in each issue of the Coordinates. Initially the chain …

Oct 2005 | Comments Off on International Terrestrial Reference Frame (ITRF)
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The International Terrestrial Reference Frame (ITRF) “yy” is a realization of the International Terrestrial Reference System (ITRS), where the “yy” represents the year of the solutions. Since its fi rst realization in 1988, there have been many variations and additions in use of data types and changes in computational strategy.
International Earth …

Sep 2005 | Comments Off on The old Indian Datum
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Under the new Map Policy, it seems that India has decided to retain the old Indian Datum, which has been identified by “Everest”, for DSMs. The following geodetic definition issues and “specifi cations” are worth commenting:
Vintage – 1880s.
Name – On a recent enquiry, four SOI experts provided four different names. However, it cannot be “Everest”.
Spheroid …

Sep 2005 | Comments Off on Malaysia precise geoid (MyGEOID)
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GPS infrastructures that have been established in Malaysia are mainly served as a ground control stations for cadastral and mapping purposes. Another element that has not been utilised is the height component due to its low accuracy. Conventional levelling is still the preferred method by the land surveyors to determine the stations orthometric height (H) with a proven accuracy. Therefore, Department of Survey and Mapping Malaysia (DSMM) has embarked the Airborne Gravity Survey, with one of the objectives is to compute the local precise geoid for Malaysia within centimeter level of accuracy. With the availability of the precise geoid, the “missing” element of GPS system is solved.

Aug 2005 | Comments Off on Classroom Geodesy
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In continuation of the discussion about the ellipsoid and geoid in the earlier interaction through the Classroom feature, let us define the reference coordinate systems. Consider a vertical axis oriented towards the north pole as Z axis. The X axis is oriented towards the First point of Aries ?. The Y axis completes a right …

Aug 2005 | Comments Off on Mumbai Floods: Another wake-up call

Maharashtra was the first state in the country to have a disaster management plan. It all started with the Latur Earthquake of 1993. As a part of response programme, the Maharashtra Emergency Earthquake Rehabilitation Project (MEERP) was launched the same year. This later led to the exercise of preparing a State Disaster Management Plan. The World Bank, United Nations Development Program (UNDP) as well as several bilateral donor agencies supported the initiative.

Aug 2005 | Comments Off on Mumbai floods: How GPS-GIS can help
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The 26th July 2005 floods in Mumbai, which caused widespread destruction, deaths and damage to property and infrastructure, have once again highlighted the importance of disaster mitigation and management using modern technology. Monitoring natural disasters like floods, earthquakes, volcanic eruptions, landslides, avalanches, cyclones, etc., with the ultimate aim of predicting them, and managing the rescue and rehabilitation operations during and after such calamities, have been discussed in various forums in the past. The devastating Latur earthquake of 1993, the Bhuj earthquake of 2001, the Orissa cyclone, and the recent tsunami after the Sumatra earthquake, which caused extensive damage in terms of human lives and property, have drawn the attention of the Indian scientific community to the immediate need of monitoring and managing such disasters in our country in the most effective, efficient and economic manner. Traditionally, maps are being used for this purpose, as an effective tool, since ancient times. However, with the introduction of computeraided techniques in map-making, and the space technology in surveying and mapping, the utility of geodetic and map data for this important activity has increased many-fold. However, a well-coordinated programme for optimum utilization of these important technological tools, resulting in efficient management of the disasters, still remains an elusive dream of administrators, scientists and technologists.