Setting Up a New Site for GPS Operations

Benefits of a well planned setup Setting up the site right – the first time! Reduces setup errors, which could result in rework Reduces time wasted on multiple equipment setups and site visits Increases productivity of machines and field crews The project is completed faster! You save time and make more money! Multiple GPS setups due to poor planning on a site could result in site systems providing erroneous information which could cause rework and added project costs Setting the site up correctly the first time will enable site crew to work on getting the project completed, rather than wasting time on subsequent equipment setups When the site is setup correctly the productivity of machines and field crews is increased - when multiple setups are performed, the machine and site positioning systems go down until the site is setup

Setting Up a Site for GPS -Topics Preliminary preparation Site reconnaissance Setting up the site Site Calibration Conclusion

Preliminary preparations Digital data – What do you have? CAD data 3D Model Who is responsible for control? Owner or you? Resources to perform in-house or contract Trimble Connected Site preparedness Internet connectivity (Land Line vs Cellular) IBSS 2-Way data

Digital Data CAD data must always be verified CAD data often must be corrected and/or enhanced Trimble Business Center – Heavy Construction Edition (HCE) data prep module can provide you with the tools to perform this task You should understand the needs of office systems vs field systems and learn what formats are needed

Control What is control? A set of points by which everything is referenced to They should be set with a high degree of accuracy Usually have been network adjusted (TBC Advance Survey Modules can be used for this) Control points are measured to “calibrate” the site for GPS-based systems You need a minimum of 3 and 5 or more are recommended Do control points exist on site? Check the site plans for control point lists and locations Check with engineer

Control Point Locations 3 points will work, but yields only 3 baselines Geometry could be weak Control should encompass the entire site

Control Point Locations 4 Points Better, 6 baselines 4th point - independent height check Geometry is stronger

Control Point Locations Optimal control- Multiple control points Geometry strongest, balanced Points encompass the site. This example - 7 points, 18 baselines.

Connected Site Connecting your site enables Remote transfer of designs TCC or email - Rovers TCC or 2-Way data - machines Remote Productivity reporting Work Order results from SCS900 Productivity tag files from machine Remote troubleshooting Trimble Assistant 2-Way data RTK Correction source delivery IBSS VRS

Connected Site Things to be aware of Internet Connectivity LAN – Comcast, Cox, etc. Stable & faster transfer rate Cellular – At&t, Verizon, T-Mobile, etc. Peak use outages Will you be using remote correction source? VRS Private or government IBSS Managed or Unmanaged Remember - these are things beyond contractor control

Site reconnaissance Size, duration, and environmental considerations Control verification GPS base station locations Correction source delivery

Size and duration of the site Size and duration of site dictates: GPS base station setup Semi-permanent installation vs daily setups? Connectivity Fixed GPS and radio network infrastructure Linear versus enclosed IBBS / Local Base VRS (Virtual Reference Station) Rebroadcast ITEMS TO MENTION: Optimally you would want to set up a site base central to the site surround by control used in calibration Conditions to keep in mind on linear projects – the first red circle indicates the primary base station location might be sufficient for radio coverage for the west side of the job, but not for the east side of the job – size of the site might dictate use of radio repeaters and / or a second GPS base station location to ensure full coverage of the job site Range Limitations - 5-10K based on line of sight, Cellular allows for significantly extended range from the base station, Correct radio antenna, High gain vs. Low gain or directional PPM error 1cm +/- 1ppm (+/- 1 millimeter for every kilometer away from base, e.g. 20km distance would equate to 1cm +/- 20mm) = GPS Base Station = Radio / Repeater

Environmental considerations Undulating versus flat terrain Urban canyons and dense foliage Radio Interference Airport radio towers Microwave towers

Control Do control points exist on site? Check the site plans for control point lists and locations Check with engineer How many? You need a minimum of 3 and 5 or more are recommended Do they provide good GPS visibility? What is there geometry relative to the site?

GPS base station - Location Set GPS antenna with 360° view of the sky. If limited try to set up with clear visibility to the equator. GPS 55° latitude limit Glonass 65° latitude limit Avoid sources of multipath Chain link fence Trees Flat, reflective surfaces Setup GPS base radio link for maximum range Elevate the radio antenna to increase range Correct antenna (high gain and low gain) Avoid sources of RF interference Microwave, radio towers Power lines Multipath occurs when a GPS antenna receives a GPS signal both directly from the GPS satellite and after it has been reflected The reflected GPS signal interferes with and corrupts the direct GPS signal, causing position errors

GPS base station Accessibility Power sources Access to where it can easily be configured, monitored, serviced, and connected to via PC Power sources Permanent or fixed power sources are ideal for long term projects (AC / fixed generators) Portable power sources - Ideal for daily usage or to provide back up to fixed power (batteries, solar panels, etc) Conditioned power is ideal to prevent power “spikes” to reduce system damage & outages Theft and vandalism mitigation Permanent setup - recommend a fixed, secure location Portable setups for rapid daily use and tear down It is important to know if a constant permanent source of power is available on site, such as a site generator, AC power from a site trailer or if a portable power source would be required, such as a marine battery on trickle charge by a solar panel or internal batteries It is important to note the local surroundings and inquire with site personnel as to whether theft or vandalism is prevalent on the job site – if so, find locations where equipment can be safely and securely stored or hidden on site, such as a job trailer with dead bolt locks, otherwise daily setups of the equipment could be required to mitigate theft. In locations that theft is a possible issue consider use of a modular receiver.

GPS base station RTK Correction source options Site Base corrections via radio Semi-permanent or Portable Local Base (over internet) Private Permanent base COORS IBSS (Internet Base Station Service) Trimble over internet solution VRS Rebroadcast (IBSS, Local Base, VRS) Connecting SNB900 to Base over internet and re-transmitting over radio ITEMS TO MENTION: Local Base - L5 signal will provide better long baseline solutions which will begin to make this a more popular solution Local Base, VRS, and Rebroadcast are commonly connected to via cellular Rebroadcast will allow machine operation but caution distance from base due to noise/PPM error

Setting up the site Why do we need a base Station? To achieve millimeter level accuracy we utilize an RTK solution. RTK navigation uses a base station receiver and mobile units What does the base station do? The Base Station sends it’s position & observations via radio to the Rover. Base station data and rover data are processed together in rover receiver to produce 3D vector Base station position + vector = rover position Result: ALL POSITIONS @ THE ROVER (S) ARE RELATIVE TO BASE POSITION Considerations GPS base station types GPS RTK Correction delivery

GPS base station types Modular – SPS852 Smart Antenna (Mobile) – SPS882

Modular GPS base station Semi-permanent “modular” GPS base station Installed on permanent structure for duration of construction project Ideal for large projects, when multiple grade control and site positioning systems are in use

Mobile GPS base station “Mobile” GPS base station for daily setup Easily setup Portable to different sites or different locations on large site SPS852 can also be used in this configuration AutoBase SPS882 & SPS852

Mobile GPS base station AutoBase Feature SPS882 & SPS852 12 base location memory 50 meter rule AutoBase Warning – SPS852

GPS RTK Delivery Method Internal radio or External radio 450 MHz and 900 MHz .5W, 1.0W, 2.0W, High Power TM3/HPB/TDL Internet Base Station(IBS) Increased range limited to PPM error deemed acceptable Cellular Ethernet LAN

Setting up the GPS base station The Good… Ideal location for semi-permanent installation – GPS antenna and external radio antenna mounted on steel “T-bar”, 360 degree view of the sky, GPS receiver and power source secure in locked area inside structure

Setting up the GPS base station The Bad & Ugly… Poor installation because: Portable GPS base station, blocked by trees and metal building, limited view of the sky – bad installation

Moving the GPS base station Before calibration – no problem After calibration – location requirement Must be moved to point used in calibration or control point measured while using calibration Same rules for calibration obtained under VRS

Setting up the GPS base station Common mistakes Antenna height errors Switching antennas Changing type, APC difference Moving base to unknown point Moving base to point measured in different reference frame

GPS site calibration What is it… Requirements

NEE GPS site calibration What is a site calibration? GPS Coordinates A measurement procedure that defines the relationship between GPS coordinates and local coordinates GPS in Latitude, Longitude, and Ellipsoid Height Local Coordinates in Northing, Easting, Elevation (MSL) We are pairing coordinates on a sphere surface and to those on a flat planar surface GPS Coordinates NEE

GPS site calibration Residuals Best effort translation between pairs (Control & WGS-84) SCS900 has a Tolerance for Calibration Value should be 50% of acceptable project tolerance Tolerance used to test calibration result worst residual We use a least squares fit – Control (assumed correct) & GPS WGS-84(errors) ITEMS TO MENTION: SCS900 has a Tolerance for the Site Calibration – this value should be at a maximum 50% of what your accepted tolerance for the project is. This tolerance is used to test the calibration result worst residual. If the calibration passes then you are good to go (but cannot try to improve the cal further – if you want to do better than the tolerance you need to change the tolerance to a tighter value) If SCS900 fails, what it does is compute the calibration n-1 times (where n is the number of points observed). Each computation uses all but one of the control points. The best calibration result will not include the point that has the most negative affect on the calibration (Hz or Vt). The worst point and worst error is flagged by the software (Hz or Vt) and that component of the point can be rejected. At that time SCS900 recomputes the Site Cal again, and checks to see if it passes tolerance. If it does you are good to go, if it fails it repeats the same process with the remaining points. It will do this loop until it gets a cal in tolerance or until the user accepts a lower tolerance. The maximum tolerance you can put into the site calibration is 0.2’.

GPS site calibration Why is a site calibration required? Allows GPS-based rover systems to work in your local site coordinate system What is needed for site calibration Onsite control base on local coordinates = GPS observation = Control Point

GPS site calibration Multi-point site calibration Requirements Minimum of 3 (3D) control points Recommend 5+ control points with good geometry for better results Combination of horizontal and vertical points - Minimums 3 horizontal control points & 3 vertical control points – or – 1 vertical + 3 horizontal + Geoid model Used when control exists and references a design frame = GPS observation = Control Point

GPS Site Calibration Control point network geometry is key = Poor network geometry = Ideal network geometry For multi-point site calibrations, control points geometrically arranged in a “line” or “clustered” in one area on the construction site is undesirable. Error in position dramatically increases the distance traveled outside calibrated site area. It is ideal to have 5 or more control points, good “geometry” of control, in the center and around the extents of the project for better site calibration results Enclose the project area with control More control points and good network geometry can improve site calibration results and identify problems early

Conclusion In conclusion, remember the key site setup steps Site reconnaissance Size, duration, and environmental considerations GPS base station location Setting up the site GPS base station setup Site calibration

Questions?