Post-Process Data Processing; Applications - ashtech Z-Xtreme System Manual

For post-process surveying

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ing along the centerline and instructing the rover system to store a position every five

seconds, for example. The result is a trail of points defining the centerline.

To facilitate the mobility required to utilize the kinematic method of data collection, the

rover system is designed to be man-portable, usually carried in a backpack. The user

interfaces with the rover system through a handheld computer/data collector.

While it is obvious that kinematic data collection has the advantage of high productiv-

ity, there are disadvantages. Accuracies are not as good as with static data collection.

In addition, the rover system must maintain lock on GPS satellites as it moves around

the project area. Loss of lock requires the user to return to one of the last successfully

established points for initialization.

Post-process data processing

Post-process GPS surveying requires that collected GPS data be later processed to

obtain results. Processing is accomplished by software included with the system.

Processing normally occurs on a PC back at the office, but can also be performed on

a laptop in the field.

To accomplish the post-processing, data is downloaded from each GPS receiver into

the computer. The processing software utilizes this data to calculate vectors between

all GPS receivers operating simultaneously. The vectors define the 3-dimensional

relationship between the GPS receivers. From these vectors, coordinates are deter-

mined for all points in the project, based on the coordinates of one or more known

points. If the survey included any redundant observations (closed loops, repeat

observations), then a least-squares adjustment can be performed to help identify any

blunders in the data and improve on the final point positions. The capability to per-

form a least-squares adjustment is included with the post-processing software pack-

age.

Post-process GPS is well suited for most surveying tasks. Systems are being used

today for control establishment, boundary surveys, and mapping applications such as

topographic, planimetric, and as-built surveys. Post-process GPS is also very effi-

cient for volumetric measurements such as stockpiles and gravel pits.

In many cases, a GPS system will be vastly more productive in these types of surveys

than a conventional total station, with the added benefit that a GPS system can be

operated by only one person.

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