For the newcomer machine guidance can be a tricky business to understand, and the number of solution providers and system types can cause much confusion.  As with my previous article over viewing the sensor options within machine guidance I would like to cut through the mumbo jumbo and give the reader an impartial viewpoint allowing them to make a clear informed choice and be able to ask the correct questions of their vendor.

This month I will attempt to provide a clear definition of the differences between the two major types of machine guidance available : 2D and 3D.

As before, my examples and explanations will be based upon the excavator model due to my familiarity with this particular application.

Note that for this article the term Machine Guidance refers to a system that will assist the operator in grading or excavating to a known design using a range of sensors to determine equipment position and an in cab display to provide the operator the relevant information.

What does 2D / 3D mean?

This refers to 2 Dimensional (2D) or 3 Dimensional (3D).  

2D - 2D is viewed as the basic system (although this term is relative as it can be quite complex in its capabilities), whereas 3D is viewed as the high end flagship system, offering complex functionality and as would be expected, due to the 3D sensing element, is more expensive than 2D.

2D will invariably refer to a system that will provide the operator with an indication of the location of the tool point e.g. bucket – relative to a predetermined target reference, this is also known as the elevation reference or Z. This indication may be numerical only (this is becoming obsolete due to the increased availability of graphic display systems) or by displaying a profile graphical model of the tool (or complete machine) and its proximity to the target line, with additional numerical information. The 2D system will not provide any information about the location of the machine on the jobsite e.g. X and Y (other than by manual references if supported by the Machine Guidance system) that is the task of the 3D system. Purists may argue that as we are only majorly concerned with elevation or Z in this scenario then this is a 1D system, but this opinion is widely scorned as we also need to know radius (and sometimes slew position) and therefore the term 2D is the accepted standard.

Examples of a 2D display:
 
and this is the important bit 3D system provides the same essential data as the 2D – location of tool point to a predetermined target – but - - has the benefit of knowing where it is on the jobsite. This positional data is usually provided by GPS, but can also be obtained from other positional data interfaces such as a Total Station. This additional information allows the excavator to be placed on to the jobsite in a format showing the excavator relative to the complete design e.g.  target layer. Unlike a 2D system which needs referencing every time the machine is moved – because it doesn’t know where it is (there are limited exceptions to this explained later) the 3D system will always show real time information of the excavator location, tool and target design. The 3D system removes the need for regular site reference points – a major cost saving in staking a site, and can provide the contractor with documented evidence of work done. The operator can work with limited supervision as all site data is available to him in the cab via the 3D machine guidance system.  A good example of 3D use compared to 2D is when digging a trench in main street or highway – 2D will know the trench dimensions , but 3D can tell the operator where the trench goes and how it is referenced to local objects such as sewage, water and electrical services.

Examples of a 3D display :
 

Functionality and Capabilities
Whilst this will not hold true for all types of 2D and 3D systems what follows is a list and description of the expected operational capabilities of these systems:

2D Systems
•    Use the system to excavate a range of profiles including level, gradients, dual slopes, trenches, complex (user defined) profiles.
•    The system can be referenced to the dig or site bench marks.
•    Excavator can be referenced to a site laser; this allows the excavator to be moved on site without the need for re-referencing to a ground based reference – removes the need for additional staking, ideal for large sites that need to graded with the excavator. This method of referencing can be accomplished in two ways :

o    An arm mounted reference sensor that “catches” the laser signal and references the excavator.
Disadvantage: Need to perform the referencing operation every time the machine is moved.

o    A motorised laser receiver mast mounted on the machine. This continually monitors the site laser reference automatically compensating for any deviation in height as the machine is moved across the site. Does not need to be referenced every time the machine is moved.
Disadvantage: More expensive than the simpler option above.

•    Tilting bucket options – if the excavator has a tilting bucket option this allows it to grade slopes from a single position whilst slewing the machine. If this is required the 2D system needs the capability of sensing the tilting bucket and the machine slew.

Example of tilting bucket display option:
 

•    System display shows both graphic and numerical data to assist on excavating to target.  Graphics can be panned / zoomed. Optional light bars can be installed to give a simple LED indication of approach to target and whether too high / low.
•    Multiple tool options to give the operator the option of selecting / creating tools including buckets, grabs, hammers etc.
•    Multiple machine storage – some of the more recent developments within 2D machine guidance allow easy transference of systems between machines. This requires the capability of storing additional machine calibration information for a quick and easy operation a useful option for someone with a smaller hire fleet that does not require machine guidance for all work. Some 2D systems offer an upgrade route to 3D.

3D Systems

A quality 3D system will have the options of the 2D system defined above with the additional benefits of:
•    Place the machine within a 3D design model giving clear indication of location and depth to target.
•    The system should be able to cope with 3D design files from a wide range of design packages.
•    A range of multiple display views showing the excavator from plan, left and right, behind and in 3D.
•    Option to select different job design layers (a design may contain many different design target layers) as well as the option to select overlays to indicate points of interest / avoidance zones and mark site points if required.
•    Progress and quality of the grade / excavation should be recorded. This data can be exported to be used as evidence of work done.
•    A simple switch between 2D and 3D operating modes. If the GPS goes down it may still be possible to continue the job using the 2D mode.
•    Can provide the ability to integrate data within a site management software suite.
Clearly there is much more functionality within all of these systems, but a lot of that is particular to certain manufacturers so in the name of impartiality the listed items give a generic overview that will give the reader a basic understanding of the subject.
It’s worth noting that machine guidance systems can be placed into 3 categories – Land based, Dredging and Specialist.  The focus of the above list is for land based applications – remember land based can cover a wide range of machines including dozer, grader, scraper, excavator, drill rig, piling rig, ground stabilisation plant, etc.
Dredging and Specialist applications will include excavator dredging, grab dredgers, suction dredgers, rock placement applications, subsea ROVs  and offer additional features such as 3D survey overlay, 3D objects, real-time update of the virtual surface as material is removed or added, volume and extraction calculations, material modelling and the design support of the relevant machine models. Specialist applications can be for all sorts of diverse and wonderful machines that just may be the subject of a future article.

Summary:
•    2D is useful within smaller projects having design areas that are of a simple nature e.g. slopes, trenches. Also a good back up option should GPS availability be limited / unreliable.
•    3D comes into its own on large jobsites due to the removal of site preparation needs and can provide necessary documented evidence of work done / to do.  Allows an operator to work without supervision and the need for site design knowledge.
•    2D / 3D Machine Guidance will improve efficiency, productivity and accuracy. Some manufacturers offer an easy upgrade route from 2D to 3D enabling the user to learn the basics of work with the 2D option and be prepared for 3D as and when its use is required. The upgrade route certainly offers economic benefits.
•    An often overlooked additional benefit both systems offer is reducing the number of people on the ground, especially the need for personnel near the machine whilst it is operating (e.g. banksman).   Apart from the obvious labour saving issues, there is a simple equation  :
fewer people on the ground = safer site.
•    No machine guidance application is too difficult be it on land, water (on or under) or for a complex machine design.

Finally, I was recently involved in a tender for the supply of machine guidance to assist within a major construction project. During discussions with the client it became clearly apparent that their expectations of the system were somewhat different to that of the equipment currently available on the market. This brings me to a very important point – we, the product designers – rely upon the feedback of the end user, it’s good to think that we create much of the product ourselves, but ultimately it’s the customer who decides if what we do is what he wants. If the offerings available to you don’t meet your needs then tell us, explain the problems you are confronted with and the tools you need to solve them, it’s the only way to progress and surely that’s good for everyone ?