OS Net® frequently asked questions

1

What is OS Net?

OS Net is a national GPS correction network. Ordnance Survey® has established a network of more than 90 permanent GPS stations around the country. From the observations made by these stations errors can be calculated in the GPS system to provide a range of correction services. 

OS Net as a service is not available commercially, however, our partners are utilising this network data to develop and provide a basket of real-time and post-process GPS correction services to customers within a wide range of markets.

2

What is a correction service?

A correction service seeks to rectify the majority of errors caused by the satellite orbits, clocks and the atmosphere.

3

What does Ordnance Survey use OS Net for?

OS Net is currently used by 130 of our surveyors to collect field data for the production of our various mapping products. The use of GPS has meant significant changes to the way we collect data and has enabled cost savings over time.

4

What are the markets for OS Net-enabled partner correction services?

Initially, high-accuracy GPS markets will be targeted. These are predominantly land surveying, engineering, civil engineering and asset management (especially in the utility arena). We then expect that other uses will be found and established – the list is long and could include precise near-shore ship navigation, road user charging, offender tracking and precision machine control in agriculture and construction.

5

Who are the partners going to be?

Organisations selected="selected" to be partners will be announced on the OS Net website and various media over the coming months.

6

When are partner GPS correction services to be launched?

The service is now available to partners and they are establishing value added GPS correction services to customers from December 2005.

7

How much will the services cost to use?

End-user pricing will be decided by partners.

8

Does OS Net support DNF principles?

Yes. We require all use of OS Net services to be co ordinated to primary coordinate reference frame (ETRS89). This means that all data collected through the use of OS Net will use a common framework and can therefore be shared and interchangeable.

9

What is the positional accuracy of OS Net?

Ordnance Survey achieves an RTK rmse accuracy of 1-2 cm in plan and 3 cm in height (though this is dependent on the user’s equipment and refers to a real-time ‘RTK’ service). The dGPS service will provide from 20 cm to sub-metre positioning (again depending on the user’s equipment). A choice of positional accuracy levels will be available for different applications and for different costs via partner GPS correction services.

10

Because Ordnance Survey uses OS Net does this mean that all their mapping products are/should be positionally accurate to 20 mm?

No. Our various mapping products are produced to a number of defined specifications, and whilst the accuracy of the data we collect is constantly improving, this does not mean that our various mapping products follow the same specification.

For raster products, the scale of the map along with techniques such as cartographic generalisation means that feature representation at the 20 mm level is not possible.

11

Europe is developing its own GPS called Galileo. Why doesn’t Ordnance Survey use that?

Our plan is that in due course we will upgrade the OS Net base-station network to receive both GPS and Galileo signals.

12

Some OS Net services are ‘free to air’ through the GPS website. Will this continue now that commercial services are available.

Yes. A free service for post-process applications will be maintained (using readings every 30 seconds) and this will continue to be available on our web site. Partners will provide higher update rate readings where they are required.

13

What are RTK, dGPS and RINEX?

These are the three key positional services available via OS Net (see the GPS glossary document for descriptions):

RTK (Real-Time Kinematic) GPS gives centimetric accuracy in real-time.

DGPS (Differential GPS) gives sub-metre accuracy in real-time.

RINEX (Receiver INdependent EXchange Format) refers to data for post- process applications.