Articles in the Geodesy Category

Feb 2007 | Comments Off on Determination of local gravimetric geoid

The demand for a high resolution geoid model has grown substantially during the last few decades especially after inception of Global Positioning System (GPS). Many countries across the world have already developed their own geoidal model which serve as the means of deriving orthometric heights from GPS observations. The impact of GPS on surveying application is undeniable. More so, this revolution has not been confi ned to the surveying community, but has extended into mapping, navigation and Geographic information system (GIS) areas. During the last few years, we have been witnessing the wide spread adoption of GPS with an equivalently
vibrant range of accuracy requirement. Many of these applications require accurate vertical positions.
The task of transforming the ellipsoidal height obtained from GPS technique to the orthometric height has prompted geodesists around the world to determine the high precision geoid undulations, for their region of interest. In India the present day nation wide geoid was computed a long time back and based on astro geodetic observations with respect to Everest spheroid. It has various limitations and does not have any signifi cance as far as GPS solutions for orthometric height is concerned.

Jan 2007 | Comments Off on North pole keeps moving south

In 1900, the International Latitude Service started to monitor the wobbling and wandering of the North Pole. Since that year, the North Pole has been moving south. In everyday terminology, it has moved secularly on the Earth’s surface in the only direction it knows, i.e., south. The total motion has been about 13.5 meter over the past 100+ years, which in other words amounts to an amazing rate of 13 cm per year or about 1 cm per month…

Dec 2006 | Comments Off on Is definition of WGS 84 correct

The first and original version of the “WGS 84”, defined by a special committee of the Defense Mapping Agency (DMA), was released in September 1987. As this task of updating the WGS 72 was concurrent with development of the North American Datum (NAD)

May 2006 | Comments Off on SIRGAS — a geodetic enterpriseL

SIRGAS (Sistema de Referencia Geocéntrico para las Américas) is a joint project of South, Central and North American countries in cooperation with some international institutions for the establishment and maintenance of a geocentric reference frame for practical and scientific use. A unique reference frame for the American continent was established by two extremely successful geodetic observation campaigns…

Apr 2006 | Comments Off on Optimizing gravimetric geoid solution

Transformation of GPS derived ellipsoidal height to orthometric height is one of the most important applications of gravimetric geoid. Its applicability remains questionable if the above transformation cannot be done to a reasonable order of accuracy. Use of GPS observations at levelling benchmarks and subsequently determined geoidal seperation using the geometrical relationship between geoid and ellipsoid (see fig. 1 )…

Feb 2006 | No Comment

Modern technologies should appropriately be blended with government developmental programmes.India is an agrarian country with about 72 per cent (about 80 Crores) of its population in about 5,75,936 villages, the villages are inhibited by the rural poor with agriculture as their predominant occupation.They are largely small and marginal farmers, agricultural labourers, artisansand scheduled castes and scheduled tribes. A large number of rural people (about 30 crore) are still living below the poverty line and often face thebasic problem of survival, viz., jobs, poverty, hunger, shelter, ill-health and disease.

Feb 2006 | No Comment

The most important ingredient for “Preparedness”.Unless we are “fully” prepared, we cannot have good and timely
response. And, to be fully prepared with good coordinates is in the
hands of geodesists, surveyors, map or chart makers, and all others,
who generate data. In turn, correct and accurate “Good Coordinates”
and quick and timely advice will strengthen the hands of the country’s
leaders, civil and/or military.If anything is lacking in good
coordinates, “We” would be failing with no room for any excuse(s).

Jan 2006 | Comments Off on Ellipsoidal heights and engineering applications

As the GPS surveying techniques started showing promise of high accuracy geodetic positioning in the early 1990s, few “open-minded” geodesists realized the possibility of using ellipsoidal heights in place of orthometric heights. Many conceptual approaches were mentioned and proposed in various applications. However, Steinberg and Papo were the fi rst to publish a paper entitled “Ellipsoidal Heights: The Future of Vertical Geodetic Control” (GPS World, Vol. 9, No. 2, 1998). As could be expected, Petr Vanicek, a geodesy professor, was quick to downplay the proposed new “type” of vertical control (GPS World, Vol. 9, No. 4, 1998). It seems that Steinberg and Papo did not “defend” their new proposal. Thus, in this paper, a review has been made to check and comment on Vanicek’s example against the ellipsoidal heights, reference to orthometric islands, and issuance of a warning for non-dissemination of ellipsoidal heights to Canadian users.

Dec 2005 | Comments Off on Geodetic infrastructure in India

The Great Trigonometrical Survey of India was completed in 19th century under leadership of the great surveyors- Lambton and Sir George Everest. It is inconsistent and inadequate. Accuracy of the network is only of the 1st order or less. First order was defined as better than only 1 in 50,000 only. Reference surface and Datum- The Everest Spheroid was given by Sir George Everest in 1830. Center of Everest Spheroid is about a km away from the center of gravity of the Earth; hence it is non-geocentric. Thus it is inaccurate and unsuitable under present circumstances. Leveling network of India has inconsistencies. Gravity observations were not carried out and not taken in to consideration. It was not appropriately adjusted. Indian Absolute Gravity Datum does not exist. Absolute gravimeters have not yet been used to define Gravity Datum in India. Topographical maps are on Polyconic projection. Assumptions and approximations accepted make it a non-projection. The earth is assumed to be fiat and there are no distortions of any kind. The projection has created problems in digitization, compilation and integration of maps. Design of the Grid adopted in India is not satisfactory. Distortion at central parallel is 1 in 824, which is quite high. There is archaic Restriction policy, which is not transparent and hinders research and development India has to make a choice between chaos and development. These problems have been discussed in detail in this paper. How India should go about to establish new geodetic infrastructure for systematic development and research, has been described in this paper.

Dec 2005 | Comments Off on Measuring geopotential difference between two points

Conventionally, the potential difference between two points P and Q located on the Earth’s surface are determined by gravimetry and levelling (Heiskanen and Moritz 1967), the drawback of which is that it is almost impossible to connect these two points in the case that they are located on two continents, because it is well known that the potential surface of the mean sea level (MSL) is not an equipotential surface. In another aspect, if given the gravity data on the Earth’s surface, one might determine the potential difference between two points by using the Stokes method or Molodensky method (ibid). In this case the potential field is determined and consequently the potential difference between two arbitrary points could be determined.