RTK-GPS Iowa

Frequently asked questions


What is the Iowa Real-Time Network (IaRTN)?

The IaRTN is Iowa's global navigation satellite system (GNSS) reference station network. The network consists of 82 continually operating reference stations (CORS) strategically placed across the state at Iowa Department of Transportation's maintenance facilities. In addition, the IaRTN uses nine Minnesota DOT sites and seven Missouri DOT sites to enhance the network along Iowa's northern and southern borders. Each site continuously relays its global positioning system (GPS) data to the Iowa DOT's computer servers in Ames, where the data is processed and sent out to the RTK users via the Internet. The network is designed to provide accurate, reliable, traceable and repeatable GNSS network corrections 24 hours a day, seven days a week, 365 days a year for the entire positioning community.

Who can use the IaRTN?

Anyone with a network-ready GPS receiver can use the IaRTN. All corrections are made through the Internet via networked transport of RTCM via Internet Protocol (Ntrip) and Transmission Control Protocol/Internet Protocol (TCP/IP).

Is there an access charge for usage?

There are no current plans for the Iowa DOT to charge users to access the network, whether from the public or private sector.

Do I need to register to use the network?

All network users are required to register with the Iowa DOT.

How does the registration process work?

Registration must be completed online, and can be accessed by the IaRTN registration link on the left-hand side of the IaRTN home page. Once completed, your account will be activated within two working days. You will receive an email containing your username and password.

Where can I get IaRTN connection information?

A link to the IaRTN connection information is available here.

What type of communication equipment is needed for RTK access?

An internal or external cell modem or a data capable cell phone with the ability to communicate with your rover and the Internet are needed to access the network corrections.

What type of cellular service do we need for RTK access?

Any Global System for Mobile Communications (GSM) or Code Division Multiple Access (CDMA) cellular data service that is capable of "tethering" will work with the network. An unlimited data plan is highly recommended, if available.

What cellular service provider do we need to use?

The Iowa DOT does not recommend any particular cellular provider. Cellular data coverage at the location where you will be working is the most important consideration in choosing your cellular provider.

What brand of GPS rover is needed?

Any brand of GPS rover of recent manufacture capable of receiving Radio Technical Commission for Maritime Services (RCTM) 3.1, RTCM 2.3, compact measurement record (CMR), or CMR+ messages is needed. In addition, current firmware allowing connection to cellular communications is required. Consult with your rover's local distributor for questions specific to your equipment.

Are Glonass satellites available when using the IaRTN?

Yes. Glonass satellites are available to those users using the RTCM 3.1 correction messages. Glonass satellites are not available to those users using the RTCM 2.3, CMR or CMR+ correction messages.

Will Glonass ever be available for CMR or CMR+ users?

There are no plans to provide Glonass satellites for CMR or CMR+ users. The network was based on an open-architecture format (universally open correction formats), and GPS satellite only CMR and CMR+ formats are being provided on a temporary basis until older GPS rovers can be replaced.

Can only dual-frequency rovers receive real-time correctors?

No, the network also provides single-frequency correctors suitable for use by professional quality mapping/geographic information system grade, single-frequency GPS receivers capable of using a cellular data modem or a data-capable phone to receive correction messages.

What is the established datum for the IaRTN?

The established datum for the IaRTN is currently NAD83(20011)(Epoch 2010.000). Originally the IaRTN was on NAD83(CORS96)(Epoch 2002.0000), but switched over to NAD83(2011)(Epoch 2010.0000) on January 7, 2013.

What is the RTK accuracy?

Assuming the standard GPS protocols and best practice methods are employed for maximum precision (i.e., good satellite coverage, good geometry of precisions, low multipath environments) the IaRTN typically achieves an RTK accuracy of 1-2 cm horizontally and 2-3 cm vertically.

Is RINEX data from the individual stations available online?

RINEX data from individual stations is available online for post-processing.

Where can I find the receiver independent exchange format (RINEX) data?

Hourly, one second sampled, RINEX data is available through the Active Rinex files and Archived Rinex files. In addition, RINEX data sets in user selectable time frames from one hour to 24 hours, with user-selectable sampling rates of 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 and 60 seconds are available through the network software using the IaRTN SpiderWeb ( Rinex downloads).

Can smaller sampling rates be provided for specific projects?

Yes, upon prior request to the Iowa DOT, data is available with a sampling rate as small as 0.1 seconds. If the Iowa DOT is are aware of your needs beforehand, a project-specific file can be created with a sample rate to meet your needs.