4Site – Infield Survey Data Capture and Real-time CAD Drawings

4Site is AiC’s data capture product based on an AutoCADTM compatible graphics engine. It has been designed to help increase productivity during a survey and reduce on site errors using either Total stations or GNNS receivers.

Some of 4Site Features include:

  • DWG based 3D CAD engine (DirectX and OpenGL)
  • Multithreaded processing, support for Windows 7 tablets and onwards
  • Fully customisable Codetable for generating CAD detail automatically
  • Support for most Leica and Trimble Total Stations
  • GNSS support via NMEA data strings
  • Traversing and Least Squares survey adjustments
  • Self-checking and raw data logging to ensure no survey information is ever lost

In its simplest form 4Site “Office” allows a user to import raw survey data and render it via its user definable Codetable into a partially finished drawing. 4Site “Survey” connects directly to a Total station or GNSS receiver for real-time data capture. This allows a user to physically see the final drawing take shape in front of them in real time.

As 4Site is based on a true DWG engine, it is not limited to a poor interpretation of what the end product may look like. It can draw pretty much anything AutoCAD does, the Codetable just needs to be pre-configured to draw the appropriate graphics.

Measurements are recorded and converted into drawing detail as they are received from the survey instrument. This information is then stored and processed internally within the DWG file, so there is no loss of data when opening the job in your own internal CAD system as everything is already stored in a CAD format.

4Site is available as either a Plugin for AutoCAD (excluding LT) or, as a standalone product which does not require such a powerful platform to run on. 4Site in its standalone guise will run quite happily on a basic Win7 or later tablet. Although a ruggedized tablet with a practical minimum screen resolution of 1200×800 is recommended.

Communications

The preferred method of communication with survey equipment is via Bluetooth. Specifically long range Class 1 (where available on both the instrument and tablet). However, 4Site also supports communications via standard serial cable connections (RS232).

The list of instruments supported by 4Site is extensive, and in general all Leica and Trimble instruments are supported. However there is also some support for Topcon and Sokkia equipment as well.

Project Settings

4Site starts each survey from a nominated AutoCAD Template (DWT) file. This file format has been extended by AiC to support all the project defaults including the Codetable which is embedded in the file along with everything else. This approach allows multiple Templates with differing Codetable and layer configurations to be created for various applications e.g. Topographic, Underground Services or Building Elevations.

Because of 4Sites DWG engine, additional data can also be imported in the same format. No conversation or degradation of the data is necessary. Full CAD drawings can be used as backgrounds for surveys, or as a source of data for setting out.

The Codetable

Unlike in a standard CAD system there are no real manual tools to generate detail, instead the CAD information is generated automatically via the inbuilt Codetable.

The Codetable works by reading the simple names or prefixes assigned to a reading (or readings) which we call a “Code”, and then rapidly looking up that Code in the table. This determines how the user would like a particular observation to be drawn.

Anything from a simple dot, to extensive combinations of symbols, shapes, complex line work, dynamic aligned text, placed onto nominated Layers with predefined Styles, Colours and Sizes, can all be drawn automatically.

Quality Checks and Raw Survey Data

4Site aims to walk surveyors and non-surveyors though the entire survey process. At all times 4Site is watching, and warning the user if there is a problem with the survey data. For instance, backsite observations with a total station are checked to see if they are compatible with the selected target. If any distances or angles are out of tolerance then warning messages will be displayed. Allowing the user to be confident that the data they are collecting is valid, and any detail they collect afterwards is in the right place. They do not have to wait till they get back to the office, before they know if the survey works and they have not missed any important detail.

Even though 4Site simplifies the survey process it is not at the expense of quality assurance and good survey practise.

Whilst the graphics screen displays the drawing, all the raw survey information that generated it, is not lost. Each and every reading is stored in the project so it can be exported and reprocessed in other survey software (like our own n4ce) should a client ever feel the need.

Ths also allows changes to the Codetable to be made live during a survey, and the entire drawing regenerated from scratch. This is only possible because the raw data is backed up fully in the 4Sites database.

As well as the project file, a real-time backup also runs in parallel to insure against battery failures or any other possible problem. No actual survey data should ever be lost, readings are automatically backed-up to a secondary file as soon as they are received by 4Site from the survey sensor.

The Survey data is stored in a Project Tree (like our n4ce system) with branches for Station control, Total Station surveys, GNSS surveys and imported CAD drawings. Edits to raw data can be made via the spreadsheet interface, whilst the survey engine has multiple reduction, Adjustment, Free station, Traverse and Least Squares networks calculation options.

Surveying with Total Stations

Total Station Instrument controls are standardised across all manufacturers. As long as the correct instrument has been selected in 4Site, the user only has to familiarise themselves with 4Site.

Once the instrument is connected and levelled, the surveyor only needs touch the instrument to point it at survey detail. 4Site will initiate the measurements and otherwise handle the instrument controls.

Obviously not all instruments have the same functionality, but 4Site is still able to unify the common controls into one interface. Therefore should an instrument go down, or an instrument with a better specification is used, 4Site just needs to be told which instrument it is now connected to and everything else continues as before.

The surveyor busies themselves with the task of getting on with the survey, and 4Site takes care of the total station whether the user is familiar with it or not

Surveying with GNSS

For GNSS surveys 4Site needs a corrected NMEA data stream via either Bluetooth or Serial cable from the antenna. This means that 4Site can be used with almost any survey grade GNSS system.

Modern antennas are capable of dialling up and accessing a correction service themselves, but if not the NMEA data can be sent out of most manufacturers controllers.

In fact any GNSS device that sends out NMEA data can be connected to 4Site. This includes modern smart phones which are capable of sub 5m accuracy.

4Site uses NMEA data that contains real-time latitude, longitude and elevation information, as well as positional dilution of precision and 2D/3D quality information to calculate the exact position of the sensor.

GNSS WGS84 coordinates are converted into UK OSGB36 Easting, Northing and Level values, and a grid projection file is used to adjust for ellipsoidal separation to calculate corrected heights.

Starting a Survey

Starting a GNSS survey is as simple as just connecting to the antenna. However starting a Total Station survey first needs control of some sort.

The Stations node in the Project Manager displays any and all survey control currently loaded into the project. New Stations can be manually typed in, imported from a text file, or generated live from a connected GNSS device.

Assuming suitable control is loaded into 4Site a new Setup can be initiated. The user has a number of possible options to select from in terms of the type of Setup they wish to start. They are…

1. Normal Backsite

Where the instrument is setup over a known point and sighted towards another known position. 4Site can then check and validate the horizontal and vertical distances which the total station measures. All residuals are reported and when tolerances are exceeded warning messages are displayed. If multiple face left and face right observations are measured, they are automatically averaged out and spreads from the norm also reported.

2. Known Bearing

Only one fixed control station is necessary. This setup method assumes the bearing is known to a particular object, or can be zeroed pointing to a backsite object. This method then allows control and detail to be surveyed without a full control network being established first. When accurate control coordinates are available for the stations, they can be re-entered and the survey recalculated to position and orientate the drawing properly.

3. Resection (Free Station)

Requires a minimum of two fixed control stations. Observations are made from an unknown position to two or more known positions. The location of the instrument can then be derived from these observations. When three or more known targets are observed then a more rigorous least squares method can be used to minimise errors and calculate the coordinates of the instrument with a far greater degree of accuracy and confidence.

4. Check Resection

As above but the derived coordinates are used to check for movement.

5. Wizard Resection

Works in the same way as a standard resection calculation, however the names of the observed targets do not need to be entered. When three or more fixed points have been observed, 4Site is able to derive the names of the stations which it has observations to and hence calculate it’s position. This method is useful when working in poor conditions, or the names of the stations is not apparent. It works especially well when the total station is equipped with a Power Search function. If 4Site detects such functionality it automatically puts the instrument into a 360degree search. Any and all targets which are found are measured and catalogued. Assuming all the relevant control is preloaded 4Site is able to use pattern recognition to deduce the names of the station is has measurements too and hence resect its position.

The Survey Interface

The Survey interface is arranged so that the most space is made available to the graphics tabs. The central window is a multi-tab interface that allows multiple views to be displayed in the same space.

Clicking on a Tab changes the view to the appropriate drawing. Each Survey will be given its own tab, which by default are given the current date followed by _TS or _GPS as their name (depending on the survey type). Any imported drawings are added as new tabs as well as the Manual Code interface and the Stations view.

Survey and Sensor controls are provided docked to the right hand side of the screen. The top half deals with functionality needed to control the current survey sensor and the most common functions to control the survey process.

Below that are buttons which bring CAD functionality to the drawing. Tools such as New Feature, Delete, Duplicate, Extend, Fillet, etc can be found here. There are too many to fit on one screen so the right hand pain scrolls vertically to allow access to the additional controls.

Selecting the Codes\Objects to Draw

During a survey Codes can be selected in a number of ways. Firstly by selecting from a list, which can be a list of all the codes in the Codetable, or from a user defined sub list which contains less codes.

For instance codes may be grouped into separate lists for Roads, Rail, Greenery, Elevations etc.. There by cutting the number of codes that are in the list at any one time, and making selections faster.

Or, if a user prefers to actually enter the Codes in manually, then a secondary interface is offered which allows just that.

As letters are entered 4Site predicts which codes start with those characters and shortens the selection appropriately. Also, as Codes are selected they go onto buttons below which store the previous eight selections. Thereby making selection almost instantaneous if one of the previous eight codes is desired.

Work with Background Mapping and Imaging

Whilst 4Site can happily load a DXF or DWG file in as a background for a survey, 4Site also offers a GIS style map view that enables a user to both check their data ties in appropriately with the real world, but to also plan a survey by leaving way points and other information on the plot which will be useful during the survey.

The Map view appears on its own tab so that switching between it and other Survey views is instantaneous. As new survey data is added to the drawing it simultaneously appears in the Map view as well.

The Mapping engine can be set to retrieve its data from a multitude of free mapping services including the likes of Bing and Google. But obviously a fast internet connection is not always available out in the field, plus it will drain the battery life. So map data can be cached at all zoom levels prior to actually going out on site.
This allows many square kilometres of data to be accessed whilst in the most rugged and remote of areas as if the tablet were connected to a super-fast internet connection back at the office.