Machine Guidance
Earth moving is required to shape the ground prior to construction taking place In this context machine guidance is concerned with guiding the operator to move the blade or dozer.
Gps On Site
scraper , excavator or grader using GPS as the reference
On the other hand , machine control is when this information is used directly to control the machine’s hydraulics to automate the blade
Initially a GPS base station is established on site
The base station collects the code and phase data and this is broadcast by radio throughout the whole site
Rover units working in RTK mode get corrections from the base station
Shortly after , position at the machine is determined with 20 - 30 mm precision at a data rate of at least 0.1 second with an even smallar latency
Usually there are two GPS antenna attached to each end of the blade so that the grade profile may be determined precisely
The machine operator needs to be guided in terms of what to do with his/her machine , therefore the GPS derived coordinates and site design components need to be transparent to the operator in the cab
The site DTM and project design are loaded into the control unit aboard the machine
As the task progresses and changes are mad to the plan these can be added either with updated physical media or by transferring the data by radio link
The operator may be guided on the task by light bars telling him/her whether to raise , lower or angle the machine’s blade or there may be a visual display of the task so that the ground a head can be compared with a design visualization
With machine guidance there is no need for conventional setting out because no profile or batter boards need to be established
The role of the surveyor is now more concerned with setting up the GPS system and ensuring that the correct coordinate systems are in use , that the GPS is functioning correctly as well as ensuring the design data is correctly formatted for the task in hand
As well as using the system to make the process of cut fill and grading more efficient the GPS can be used to do a survey of the work achieved so far on a daily basis
This can be used to calculate payment for the task and to determine whether the specification for the work has been achieved
The same design file can be used for the initial rough cuts and moves of mass of dirt as well as the finished grades
Where the GPS is interfaced to the machine’s hydraulic valves there can be automatic control of elevation and cross - slope
For large sites where parts are beyond the range of the base station radio repeater radios may extend operations up to about 20 km
GPS has its limitations in terms of the precision that can be achieved in real time
If the system is augmented by lasers then final profiles can be achieved down to a few millimetres
Cut and fill to planes defined by conventional profiles and batter boards can easily be achieved
What is more difficult is to create a smooth surface defined by vertical profiles in more than one direction such as in landscaping , especially golf courses
With a DTM and GPS machine control this is more easily achieved
GPS antennae mounted om masts attached and robust
Antennae are expensive and therefore vulnerable to theft and damage when the site is not active or guarded
Using GPS means there will be fewer personnel such as surveyors on site and therefore the site becomes safer
Where there are areas of danger on the site which are invisible to the operator , such as pipelines or contaminated ground , they can be included in the data for the control unit and an audible warning given to the operator if the machine gets too close
Plate tectonics
Plate tectonics is centred on the theories of continental drift and is the most widely accepted model describing crustal movement
GPS is being used on a local and regional basis to measure three dimensional movement
Locally inter station vectors across faults are being continually monitored to millimetre accuracy , whilst regionally , GPS networks have been established across continental plate boundaries
The information obtaned adds greatly to the study of earthquake prediction , volcanoes and plate motion
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