Ashtech Z-Surveyor Service Manual download pdf (Page 11)

Introduction 3

Introduction

the other(s). The positional relationship between the receivers is presented in the

form of a vector, i.e. (delta X, delta Y, delta Z) or (delta N, delta E, delta H)

between the receivers. This is a 3-dimensional relationship. It is analogous to a

conventional observation of (horizontal angle, vertical angle, slope distance).

Vectors are produced between all combinations of GPS receivers used during the

survey.

It’s important to remember that GPS observations result in vectors defining the

relationship between the points observed. That is, a vector is the result of a GPS

observation, not the coordinates of the surveyed points. To determine

coordinates of surveyed points, a set of coordinates must first be supplied for one

of the points. Based on this set of coordinates and the GPS vectors observed for

all other points, coordinates for the other points can be computed. In this manner,

coordinates for the newly surveyed points are determined. Similar to a

conventional traverse, your initial set of coordinates can originate from a known

control point incorporated into your survey. Alternatively, assumed coordinates

can used.

Post-process GPS Surveying

Post-process GPS surveying can be broken down into two primary tasks, data

collection and data processing. Let’s examine each task in detail.

Post-process Data Collection

Data collection can be performed using two different methods; static and

kinematic. Following is a description of each method.

Static Data Collection

As the name implies, static data collection is stationary in nature. The GPS

systems simultaneously collect raw data from all available satellites while

remaining stationary on their respective points. Data collection continues at these

locations for an amount of time dependent upon distance between the receivers,

satellite geometry, and obstruction conditions at the data collection locations (for

example, trees or building blocking some of the sky). When data collection is

complete at these specific points, the GPS systems may move to a new set of

points to begin another static data collection session. In most cases, one GPS

system will remain on its current point in order to link the previous set of points to

the new set of points. After data collection is complete, data is downloaded to a

computer for post-processing. Processing will compute vectors to determine the

position of all points observed.

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Ashtech Z-Surveyor Service Manual Page 11