What is it?

Q. What does OmniSTAR do, and what products do you sell?

A. GPS (Global Positioning System) has become a ubiquitous tool for any endeavor where a quick measurement of geodetic position is required. Examples range from tracking moving objects to establishing the exact location of physical assets. Current GPS equipment is small and reasonably priced and is finding its way into new applications every day.

However, GPS does contain both Systematic and Random errors. The only proven methods for correcting the errors are (1) post-processing using GPS measurements collected at known reference points, and (2) the use of "monitors" at known locations to measure the errors, generate corrections, and send them to other "users" as quickly as possible - commonly called "real-time differential". Early use of this DGPS technique utilized UHF radios to send the corrections to nearby users.

In 1987, the OmniSTAR group developed a method of using the corrections from several sites and weighting them to give the user an "optimized" set of corrections. This was called "Wide-Area" DGPS and it led to using Geostationary Satellites to broadcast the corrections over large areas.

Today, OmniSTAR continuously monitors the signals of all GPS satellites at over 100 known locations around the world, 21 of which are in North America. The "monitors" (Base Stations) measure the errors from all GPS satellites in view at their locations and compute corrections. If these corrections can be delivered to "users" quickly, they can be used to remove most of the errors. OmniSTAR utilizes several commercial Geostationary Satellites around the world to "deliver" these corrections to customers. For the VBS solution the correction data is in a standard format called RTCM-104 that is recognized by virtually every GPS receiver. The result is a real-time sub-meter correction for the user's GPS measurements. HP and XP are proprietary solutions derived within the receiver using carrier phase measurements to provide decimeter accuracy.

This system of measurement and delivery of corrections to our Customers is in the form of a "Subscription Service". Customers "Subscribe" to our service for a fixed period, usually one year, for a fee. The subscription fee and options for subscription duration are  dependent on the area of operations. This worldwide system of real-time measurement and delivery of GPS corrections (Differential GPS) is the primary business of OmniSTAR.

Q. How can I get OmniSTAR?

A. In order for a user to receive the OmniSTAR corrections, an OmniSTAR-Enabled Satellite Receiver must be utilized for receiving and decoding the OmniSTAR data. Several GPS manufacturers have incorporated the special OmniSTAR receiver into their own GPS receiver packages. Trimble, Satloc, CSI, NovAtel, Starlink, Topcon, AGCO, Case IH, Raven Industries, and Ag Leader all have GPS systems with fully integrated OmniSTAR. OmniSTAR-Enabled Receivers may come with a one-year subscription as part of the package. If not, you may call OmniSTAR or your GPS supplier to have your subscription activated over the Satellite. It takes only a few minutes.

Where can I use it?

Q. Does OmniSTAR work everywhere?

A. A qualified yes. First, OmniSTAR has satellite coverage over most of the Land areas of the Globe, with the exception of some areas beyond 60 degrees North and 60 degrees South Latitude. However, even within the coverage areas, the user must have a clear line-of-sight to the local OmniSTAR satellite. In the USA the elevation of the satellite above the horizon ranges from over 55 degrees to about 30 degrees depending on location.

Q. Can I take my OmniSTAR receiver to any of the covered land areas and use it?

A. Any OmniSTAR L-band receiver or OmniSTAR-enabled receiver is capable of being used in any OmniSTAR coverage area. Your OmniSTAR-Enabled Receiver must be set to the proper frequency of the local Satellite and you must have a valid subscription for that area.

Q. How do I obtain a subscription for a new area?

A. You can call any of the three OmniSTAR Regional offices (Houston, Holland, or Australia), give them your equipment serial number, arrange payment, and they will send the new subscription over your local satellite.

Q. Is there a Global subscription that will allow me to work anywhere?

A. Yes, contact your nearest OmniSTAR regional office for details.

Q. Where is the North American OmniSTAR Satellite located?

A. The MSV Satellite we use in North America is located at 101 degrees West Longitude. It is over the equator, roughly south of a line through Denver and El Paso. Its altitude is relative to the user's latitude. Along the southern states it's 50 to 55 degrees above the horizon. Along the Canadian border, the altitude is 25 to 30 degrees above the horizon. At 60 degrees North, it's down below 20 degrees. When it is at 5 degrees or lower, it is very difficult to get a clear line-of-sight.

Q. How far South does the MSV coverage extend?

A. The exact point is not known. It appears to give very reliable coverage to at least Mexico City. Several users have reported using it as far south as the Guatemalan Border.

Q. What is the coverage for Central and South America?

A. Central and South America is covered by AMSat, located at 98 degrees West.

Q. Will my OmniSTAR work in near-shore areas or in bays?

A. No. OmniSTAR is designed as a land-only system. In fact, the OmniSTAR User Agreement specifically prohibits use beyond the coastline. The Fugro Marine Survey group has products specifically designed for marine use.

How do Subscriptions work?

Q. How can I tell when my current subscription will expire?

A. Some units will show the "End Date" or Expiration Date on the display. If we have an "owner of record" in our database, you will receive a mailed notice approximately one month prior to expiration. You may also call the OmniSTAR office that issued the subscription. They will have the information on file, by serial number.

Q. What happens when my subscription expires?

A. That is model specific. Some will continue to output, but the data will be uncorrected. Others may stop output altogether.

Q. Does OmniSTAR sell partial-year subscriptions?

A. Partial-year subscriptions are available in Europe, Africa and Asia. In North and South America, where subscriptions are less expensive, partial-years are not currently being sold except for the 100-day HP Ag subscription.

Q. Can I purchase a subscription renewal ahead of time without penalty?

A. Yes, subscription renewals are simply added to your existing subscription date.

Q. Can I subscribe after working hours?

A. Yes, for North or South America, you can get a 24 to 72 hour subscription - at no cost - at night or during a weekend. You will need to call again during the next working day to keep it going.

Q. Can I subscribe over the Internet?

A. No. We have found it beneficial to subscribe while the customer is on the phone. The subscription and proper operation can be verified with a single phone call, usually within 5 to 15 minutes.

Q. How do I obtain a subscription for a new area?

A. You can call any of the three OmniSTAR Regional offices (Houston, Holland, or Australia), give them your equipment serial number, arrange payment, and they will send the new subscription over your local satellite.

Q. Is there a Global subscription that will allow me to work anywhere?

A. Yes, contact your nearest OmniSTAR regional office for details.

What can I expect for accuracy?

Q. What accuracy can I expect?

A. Accuracy can only be predicted in statistical terms. In general, the accuracy depends on the quality of the GPS receiver used with OmniSTAR; that is, a "Recreational" class GPS will give poorer results than a "commercial quality" receiver. In this case, "poorer" means larger semi-random errors relative to the true position. While you may occasionally experience a small error with this type of receiver, a few minutes later or the next day may give you an error of many meters. The better "Commercial" GPS receivers can achieve horizontal errors of less than a half-meter 67 to 73% of the time, less than a meter 95 to 97% of the time and less than 1.5 meters 99% of the time. Vertical error will be 2 to 2.5 times greater than the horizontal error. OmniSTAR XP and HP horizontal accuracies are normally < +/- 15 cms and < +/- 10 cms respectively > 95% of the time.

Q. What datum is OmniSTAR on?

A. OmniSTAR VBS in North America is on the NAD83 datum and ITRF00 in all other OmniSTAR world areas. OmniSTAR HP and XP are in ITRF00, worldwide.

Some GPS receivers have the capability to convert and output the Position Data in various datums. This is a choice made by Receiver Manufacturers. Check for this option and your receiver settings to be sure.

The reason for keeping the VBS in NAD83 in North America, is somewhat complex. When GPS was first installed in 1984, WGS84 matched NAD83, because it was a U.S. system. However, over the years, GPS has gradually moved to the new world datum, ITRF. OmniSTAR has elected to keep its North American VBS system on the NAD83 datum to stay consistent with prior VBS survey data.

Q. Does Averaging improve my position fix?

A. Not necessarily. The errors that remain after differential corrections tend to be long term and somewhat random. We have observed that 24-hour data sets are very repeatable and improve the absolute accuracy, but shorter samples may not.

Q. Should I plan my work around the "best" times for GPS?

A. With a few exceptions, GPS is now available 24-hours with a sufficient number of satellites for a good fix. If you run your GPS with a 5-degree altitude mask, you should have good data around the clock. The exceptions are occasional periods when certain GPS satellites are being moved or are down for maintenance that you may experience short periods of high DOP. Those periods usually last for an hour or less and are repeatable for several days.

Q. Does it matter where I am relative to an OmniSTAR Base Station?

A. No, within reason. OmniSTAR uses a unique Wide Area Solution that gives a constant fix quality, regardless of the user's location. Every user set uses correction data from all OmniSTAR Base Stations, but the correction data from each Base Station is weighted relative to the user's location. It's all done within the user's equipment, so that every user gets an optimized correction - for his unique location. Some other systems have a less than optimal solution that forces a user to use corrections calculated for a number of fixed locations, where the user set picks the nearest one. That type of solution has a built-in user error of approximately 1-meter for every 100 miles from the fixed location. The global network of OmniSTAR reference sites means that in most areas of operation (North America, Europe, Australia, East Asia, etc.) there is appropriate data available. In very remote areas, such as mid-Ocean islands or in Central Asia,  then the OmniSTAR XP solution is recommended.

Q. What value should I use for my GPS Receiver's "Altitude" or "Elevation" "Mask"?

A. The Omnistar network outputs corrections for all satellites that are at 5 degrees or higher at any Base Station. While the user should make their own decision, our observations indicate that an acceptable solution is available 24-hours with a 5 degree mask. A slightly more conservative setting would be 8 degrees.

Operational Questions.

Q. What is NMEA?

A. The acronym stands for "National Marine Electronics Association" and is again an industry association that sets data transmission standards. In this case, the real name is NMEA 180. It is a set of standard messages defining the possible outputs of a GPS receiver. There are several "sentences" available; each of which has some unique data associated with them. They are all in ASCII format and are in the form of comma delimited strings. String lengths vary from 30 to 100 characters and are output at the interval chosen - again usually once per second. The most common string (or sentence) is called the "GGA" string. It contains the Time of the Fix, Latitude, Longitude, Height, Number of Satellites used in the fix, DOP, Differential Status, and the Age of the Correction (RTCM). Others have Speed, Track, Date, etc.

NMEA is available in virtually all GPS receivers and is the most commonly used data output format. It is also the format used in most software packages that interface to a GPS receiver.

Q. How often will I get a fix from my GPS receiver?

A. This question is often preceded by "How often does OmniSTAR transmit corrections"? The perception is that a user will only get a position fix when a new correction is received from OmniSTAR. That is not the case. The user's GPS receiver will output at the selected rate (usually at 1-second intervals, but for auto-steer applications it may be > 10 times per second), regardless of the corrections. The ability to continue solving for corrected positions between differential updates is based on the fact that the errors in GPS - with SA turned off - change very slowly and a correction will be valid for several minutes. When SA was "On", the errors changed very rapidly and corrections had to be updated every few seconds. This is no longer the case.

Q. What is RTCM?

A. The correct name is RTCM-104, Version 2 or 2.1. The acronym stands for Radio Technical Committee, Marine and is the name of a committee that governs standards for passing data between different equipment used in the Marine Electronics Industry. In the early days of Differential GPS, they set up a standard format for sending differential correction data to a GPS receiver. The actual format is complex and lengthy, but it contains three main elements: (1) The time of the measurement at the Base Station, (2) measured range errors (Corrections) for every satellite in view at that Base Station, and (3) the "range error rate" for every satellite in view.

As explained above, the Range Rate term is currently set to a zero value. If SA were to be turned back ON, the rate term would be measured and sent in every message.

Q. Is OmniSTAR susceptible to interference?

A. The older C-band OmniSTAR units (Model 7000) were susceptible to a certain type of interference generated by the Telephone Co. Microwave towers. If they were close enough to our frequency or if the user was very near to them, they could totally block the OmniSTAR Receiver. Newer units, which use L-band frequencies, are not susceptible to that particular source of interference. However, normal precautions should be used when using radio receivers near anything that generates noise. There have been reports that certain cell phones and certain laptop computers can cause problems when they are in close proximity (a few feet).

Q. How does OmniSTAR compare to the Beacon Service?

A. OmniSTAR VBS is superior to Beacons in Reliability, Accuracy, and Coverage. Beacon users usually have only one beacon within reliable range. If it goes down, there are no alternatives. OmniSTAR had a 99.7% on-line reliability in 1998. Beacons have a possible accuracy problem, in that there is a built-in bias error of about 1-meter for every 100 miles from the beacon location. If a user switches from one beacon to another, the position fix difference may be twice that value. Lastly, OmniSTAR covers the entire continent, versus limited beacon coverage. In summary, OmniSTAR is a Commercial Service which is responsive to its customer's needs, as opposed to a free government-run service. (Who do you call if a beacon goes down?) OmniSTAR XP and HP are an order of magnitude more accurate.

Customer Service

Q. Does OmniSTAR charge for customer Service?

A. No. We do not charge for Customer Service phone assistance. An employee will answer our Customer Service number 24 hours per day, every day. No phone mail or automated phone system. You will always get an answer to your request or question, even if it means a callback. Subscriptions are also available around the clock. You will find we are extremely customer-oriented.

Q. How does OmniSTAR handle emergency repairs to my equipment?

A. During the warranty period, if your OmniSTAR equipment stops functioning, and we cannot resolve it over the phone; we will ship you a replacement unit, that same day, with overnight delivery, at no cost to you. If it is agreeable to OmniSTAR and the customer, we will usually propose that we simply exchange units permanently, as opposed to shipping and replacing again after repairs are made. The remaining warranty and subscription would be transferred to the replacement unit. This exchange policy is applicable for all OmniSTAR-manufactured hardware. It may or may not be available for "OmniSTAR-enabled" equipment from other manufacturers. Check for specific information on other brands.

After the warranty period, we will repair OmniSTAR units on a time and materials basis. We may, if available, agree to make an exchange on out-of-warranty equipment for a reasonable fee. This will insure minimal down time for the customer.