1.
The science and technology of acquiring , storing , processing , managing , analyzing and presenting geographically referred information (geo-spatial data ). This broad term applies both to science and technology,and integrates the following more specific disciplines and technologies including surveying and mapping ,geodesy , satellite positioning , photogrammetry ,remote sensing, geographic information system(GIS), land management ,computer systems ,environmental visualization and computer graphics .
2.
A horizontal angle is the angle formed in a horizontal plane by two intersecting vertical planes , or a horizontal angle between two lines is the angle between the projections of the lines onto a horizontal plane .For example ,observations to different elevation points
B and
C from A will give the horizontal angle BAC which is the angle between the projections of two lines (AB and AC) onto the horizontal plane . It follows that , although the points observed are at different elevations ,it is always the horizontal angle and not the space angle that is measured . The horizontal angle is used primarily to obtain relative direction to a survey control point ,or to topographic detail points ,or to points to be set out .
3.
The first step in measuring the distance between the GPS receiver and a satellite requires measuring the time it takes for the signal to travel from the satellite to the receiver . Once the receiver knows how much time has elapsed , the travel time of the signal multiplies the speed of light (because the satellite signals travel at the speed of light , approximately 186,000 miles per second )to compute the distance . Distance measurements to four satellites are require to compute a 3-dimensional (latitude ,longitude and altitude )position .。