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A subscription cost $200 per month per each individual access. This is paid to the City of Albuquerque. An internet capable mobile phone, or equivalent device, costs whatever the mobile phone service provider charges. Currently this has been about $50 per month per device. The cost of the device, of course, also varies depending on which model is purchased.
A subscription works for one single internet access to the system at a time. This can be transferred from one survey controller device to another and differing employees within a company can use the access but, because of liability constraints, it cannot be transferred to an employee of another company that has not signed an agreement with the City.
There are a variety of ways to do this and ultimately it is up to the user to employ sound surveying practices in using the network just as they are expected to use sound surveying practices when using any other positioning technology. There are various ways users accomplish this. One of the most common approaches is to check into several control points near their project area after connecting to the network and before commencing work. Fortunately the City of Albuquerque has about 1400 active control points that can be used for this purpose. In some situations, site specific privately set control points are appropriate for this purpose. Other situations call for different approaches. Ultimately it is up to the user to decide how to best accomplish this fundamentally important task. Technical support for the equipment the user is using will provide information on how to apply the surveying practices selected using their specific software and hardware.
Positional accuracy attained by users of the ARTGN depends on a variety of factors. In order to evaluate positional accuracy, the user will need to know how to evaluate positional accuracy using current RTK methods. In general, the same accuracy factors that effect RTK positioning effect positioning with the City System and in the same ways.
The City of Albuquerque has checked positioning accuracy in two general ways, checking the accuracy of repeat positions on the same random point and the accuracy of positions relative to existing City of Albuquerque control points.
Repeat positions of the randomly selected point indicate the internal accuracy of the system with its combined rover equipment setup. These kinds of positions usually are within 0.02 ft. - 0.07 ft. from the horizontal average of multiple positions. Occasionally horizontal positions will range up to 0.15 ft. from the average. Vertical values usually range a bit higher +/- 0.08 ft. - 0.17 ft. Occasionally vertical errors range up to +/- 0.25 ft. These horizontal and vertical variations are dependent on many factors and the user needs to be aware of their effects in considering how to use the system for a specific job with its specific accuracy requirements. How many satellites are visible from the site, and their geometric arrangement have a tremendous impact on accuracy. Site specific obstructions such as trees, buildings, vehicles, can alter geometry either by obstructing a satellite, attenuating its signal or causing multipath delays that vary from one antenna orientation to another. Varying conditions of the surface of the sun can have tremendous impact on GPS signals and are difficult to predict. Accuracies generally degrade the further one is from a base station. And finally some inaccuracies cannot be completely accounted for.
The City of Albuquerque has also checked positions relative to nominal published positions of the City's control points. With this method the internal errors of the system and rover are augmented by unavoidable system error in the control point positions. Regardless, positional accuracy with this method has been about the same as with the previously described method.
Vertical accuracies can bring in additional factors. The City of Albuquerque has not systematically checked vertical accuracies using either a geoidal model or checking against nominal values of points that have established NAVD88 elevations. The system is fundamentally a system that provides positioning in ellipsoidal values of NAD83 and does not directly provide information about orthometric, spirit-level heights. Generally users have to do a local site vertical calibration to generate adequate orthometric heights. Again this depends on accuracy needs but, this is often the case. Satisfactory orthometric heights can best be generated by a site calibration using four or more benchmarks with adequate NAVD88 orthometric known values and which are distributed well about the area of the project site. Application of a NGS, or other source, geoidal model also works well in some circumstances. It depends on the user accuracy needs and the other factors discussed above and the user is responsible for evaluating the situation and making judicious decisions about which method to use. The system is definitely not a "black box" which somehow provides accurate enough positions for any or all surveying positioning needs. The user is responsible for final accuracies and must employ adequate methods to check results for accuracy.
Support has to be a cooperative venture between City, dealer support, local users and the documents on this site. No one source can provide support on all aspects of using the system. Please look through this FAQ page and check the Equipment Setup page. If you are still not sure where to turn, contact us at the link to the left. If we cannot help, we will be able to point you in the right direction.
The system is designed for generic use so a wide variety of equipment can be used. The user equipment does not have to be from any particular manufacturer.
Basically the user needs an RTK capable system and a way to connect to the internet and stream data through the internet to the rover GPS unit of the user and back to the system. This can be done in a variety of ways using a variety of types of equipment.
Frequently our users do this with the following setup:
a. A recent model GNSS unit set up for RTK operations
b. A recent model GNSS survey controller unit that will utilize NTRIP for communication with the internet.
c. A SIM mobile phone card with an internet data plan by a service provider.
d. A modem device such as Enfora for connecting the rover unit to the internet.
The user has to contact equipment manufacturers to confirm that their equipment will work with wide area networks, communicating through the internet using NTRIP. The best choice is invariably the newest equipment. Some of the older systems simply do not have the internal characteristics necessary to work with the Internet, mobile phones and NTRIP. Please contact local systems users about this. Manufacturer technical support must ultimately be contacted to work out any remaining issues.
If it is fairly new, it probably will. Older systems are more problematic. Refer to the question "What equipment is required to use the system?" for more information about this.
In general, yes. But, as always, there are exceptions. The system is designed to be generic and operate with various types of equipment. The exceptions have to do with the particulars of how the equipment works rather than the brand of equipment. Refer to the question "What equipment is required to use the system?" for more information about this.
The City of Albuquerque purchased the system and owns and operates it.
It has been quite reliable. The City of Albuquerque makes every effort to keep the system up and running 24/7 but, cannot guarantee complete connectivity all the time. We have a dual server system to switch to if the main processing software goes down. We also have back-up, redundant connections at most of the sites. However, sometimes some parts of the system do go down and the user has to have a contingency plan for those occasions.
Yes. See the RINEX Downloads page for more information.
The user needs either a mobile phone with an internet data plan or some other device to connect to the internet from the field.
Any service provider will work but some work better than others. Area coverage, technical support and rates vary among providers. Please consult the manufacturer of your equipment to ensure compatibility and talk to local users about this.
Whichever has the best support local, phone or internet. Various types can be used but refer to "What equipment is required to use the system?" for more information.
The system transmits positional data in NAD83. It does not transmit positions in WGS84.
The system is not using a vertical datum such as NAVD88 or NGVD29. It transmits vertical positional data in NAD83 ellipsoidal values. The user has to use additional means to derive the orthometric heights that are normally derived from vertical datums related to a geoid. These methods include local calibration to control points that already have NAVD88 values, application of a geoidal model or some other approach.
(Note: we are using these three terms interchangeably).
As is the case with nearly all surveying operations the user undertakes using the network, the answer depends on the specific needs of the user. Certainly a transformation will be necessary if a user wants to pick up an existing project and use a previously defined coordinate system with an arbitrarily chosen origin. Projects done in NAD83 may or may not require a calibration depending on how closely points need to be set relative to any pre-existing points. Vertical only calibrations are quite often done by our users as a necessary procedure to obtain satisfactory elevations. Refer to other questions on this page that deal with this issue.
Since this depends on what kind of accuracy the user needs, there is no single answer to this question. Whatever distance limitations the user normally uses with RTK operations apply to the system network. Many users routinely use our system with base stations up to six or even ten miles away. For most RTK operations six miles is safe. Users sometimes get satisfactory results from ten to thirty miles away but, the process becomes less dependable and accuracy degrades at those distances. So having a satisfactory method to check onsite accuracies is critical to all network operations but becomes even more important as the user moves beyond six miles from any of the base stations.
The system operates 24/7 although system management personnel are only there from 7:30 AM to 5:00 PM Monday through Friday.