4.0 Impact of limited funds on executing projects
Planned projects remain uncompleted for long time, and cause some conflict when being late on implementation. For example any cadastral survey in Tanzania by the law require to use town planning proposed drawings to guide any demarcation which is being done. But town-planning drawings are normally prepared using outdated base maps with neither field verification nor any details are being picked in the site. This brings about conflict with cadastral plans due to lack of parcel/plots conformity after field survey. Instead of starting with, Planning, Surveying, Building and Occupation (PSBO) we are falling in Building, Occupation, Planning and Surveying (BOPS) popularly known as squatter upgrading.
Densification of controls as a base for any subsequent survey requires enough money for monumentation and field execution especially in the traditional survey environment either aerial survey projects which are required for ground photo controls in the case of base maps preparation or field completion need enough money which are not available.
4.1 High demand of surveyed land
Demand for surveyed parcels of land in urban areas is very high for example in Tanzania, is increasing daily due to people migrating to urban centres from rural areas seeking employment and better social amenities and natural increase of population. Lack of funds for surveying parcels of land in time and the awareness of people to own the surveyed and register land, have been noticed as one major problem.
5.0 Global Positioning System (GPS)
The Global positioning System was developed to replace the U.S. Navy Navigational Satellite System (NNSS), also called TRANSIT or DOPPLAR System. This System was composed of six satellites orbiting at altitudes of about 1100 km with near circular polar orbits. The TRANSIT System was developed by the U.S. Military, primarily to determine the positions by co-ordinates of vessels and aircraft. Civilian use of this Satellite system was eventually authorised, and the system became used worldwide both for Navigation and Surveying. The GPS was developed to replace the TRANSIT system because of two major shortcomings in the earlier system.
1.The main problem with TRANSIT was the large time gaps in coverage. Since normally a satellite would pass overhead every 90 minutes, users had to interpolate their position between ''fixes'' or passes.
2. The second problem with TRANSIT system was its relatively low navigation accuracy.
In contrast, GPS answers the questions ''what time, what position, and on what velocity is it?'' Such questions are answered quickly, accurately, and inexpensively anywhere on the globe at any time. Remondi (1991).
5.1 Space Segment (Satellite Constellation)
The Space Segment of the system consists of 24 GPS satellites. In-order to provide a continuous global positioning capability, a scheme to orbit a sufficient number of Satellites, to ensure that at least four were always electronically visible, was developed for GPS. Figure 1 shows the system consists of constellation of 24 satellites (21 satellites constellation with 3 active on-orbit spaces) in six evenly spaced orbital planes placed in circular 12 - hours orbits inclined at 550 to equatorial plane. In any event, this constellation provides a minimum of four satellites in good geometric position at any of the 24 hours of a day anywhere on the earth's surface. Depending on selected elevation angle, there is often more than the minimum number of satellites available to enable the receiver to compute the position, velocity and time. Four GPS satellite signals are used to compute positions in three dimensions and the time offset in the receiver clock. It is during these periods of 4 satellites and above that Surveyors perform any method of GPS Surveys Figure 2. In fact, assuming a 100 elevation angle, there are brief periods where up to 10 GPS Satellites are visible on the earth's surface.
5.2 Global Positioning System is a solution technology
Advancement of space technology lead to develop Global Positioning System (GPS), although it was intended to be used to different purposes in army activities. The alternative of surveying is another reported a timely breakthrough to rescue the aforementioned problems. It is a multipurpose system, which has done marvellously especially when the World is entering the new millennium by determining the position of any point on the earth instantaneously. Ships and aircraft track their location, velocity and time through GPS. GPS is the best for networking, provided the space between antenna of the receiver and sky is clear and at least four satellites are available. That measurement provides World Geodetic Co-ordinates (WGS84) in three dimensional co-ordinate systems that is fixed to the earth and has its origin at the centre of the earth. During measurement requires occupying at least three local known points for our case in Tanzania of UTM co-ordinate system to be used to determine parameters for transforming from WGS84 to the mapping plane.
