1. Introduction

OP is a web-based geodetic application which enables the baseline processing of simultaneous, static GNSS observations, called sessions, followed by a least squares adjustment of the sessions. Results are tied to the National Spatial Reference System (NSRS). Collectively, the data, session solutions, least squares adjustment, and additional metadata are called a project. OP provides a user-friendly map and graphic interfaces to visualize the project and solutions. It also provides useful quality assurance, and quality control functionality as well as file organization features to assist in processing. The new OP builds on the success of previous versions of the application to provide the same look and feel and ease of operation, but fully replaces legacy methods of PAGE-NT GPS processing and NGS ADJUST software programs, and provides an updated method of submitting least squares adjusted, campaign-style GPS projects to NGS.

The latest version of OP allows for the inclusion of GNSS Vector eXchange (GVX) formatted files. GVX aims to provide a standard format for exchanging GNSS vectors derived from varying GNSS survey methods and manufacturer hardware. The file format includes all of the necessary data of a GNSS vector for inclusion in a survey network for least squares adjustment, as well as metadata which describes the vector. The format is capable of containing any type of GNSS vector, whether it was derived in real-time (RTK or RTN) or from baseline post-processing.

While NGS does not provide tools to translate your vector data files to GVX, we have integrated the use of GVX into OPUS Projects. This provides users the ability to include RTN-GNSS positions in their projects, and to even submit that data to NGS for publication on Datasheets.

For details on GVX file format, see: https://geodesy.noaa.gov/data/formats/GVX/index.shtml

Access to OP is through the Projects link on the OPUS upload web page at http://geodesy.noaa.gov/OPUS/, or directly using the URL: http://geodesy.noaa.gov/OPUS-Projects/. The OP create, session, and manager access page is showing in Fig. 1.1.

OPUS Projects Create, Session, and Manager access page at https://geodesy.noaa.gov/OPUS-Projects/

Fig. 1.1 OPUS Projects Create, Session, and Manager access page at https://geodesy.noaa.gov/OPUS-Projects/

To create OP projects, the user must have completed the OPUS Projects Manager Training. Training options include both in-person classes and webinars. To see the availability of and register for a live workshop, go to the NGS Calendar of Upcoming Classes. To access online materials visit the web page for the NGS Testing and Training Center. To request additional training, contact ngs.training@noaa.gov or your regional geodetic advisor.

Upon project creation, a set of unique keywords is automatically created, which provides online access to the project. To add data to the project, a user uploads static GNSS, dual-frequency observation files to OPUS, providing the specific antenna type, the vertical height to the Antenna Reference Point (ARP), and the project ID keyword referred to above. After uploading all static GNSS files, OP performs session baseline processing using the same software that has traditionally been used in the bluebooking process (PAGES).

Once the user moves on to the Network Adjustments phase, the workflow shown in Fig. 1.2 depends on whether the user has previously associated a Project Tracking ID to the project. Without a Project Tracking ID, the software GPSCOM is used to compute any and all adjustments the user wishes to specify. Conversely, if a Project Tracking ID (either the ID assigned thru the Survey Project Proposal process, or the default ID “0000”) has been associated with the project, then GPSCOM is used to compute a Preliminary Adjustment while a subsequent, sequential set of adjustments (Horizontal Free, Horizontal Constrained, Vertical Free, Vertical Constrained) is computed using ADJUST. Please refer to the Glossary for more information on these programs.

Caution

The user should decide at the outset which network adjustment process is required to meet project objectives (i.e. with NGS Project Tracking ID or without). Once a NGS project Tracking ID (or default ID) has been associated with the project, it cannot be un-associated with that project. An official NGS Project Tracking ID, however, can always replace the default ID (but not the other way around!).

The decision of whether to use ADJUST or GPSCOM will be primarily driven by whether or not the user intends on submitting the project to NGS. If that is the goal, then the project must have an official Project Tracking ID assigned. Users not interested in submitting to NGS may still want to ensure that their project remains aligned to the latest realization of the NSRS or their project contains GVX vectors. In that case, the default tracking ID “0000” should be used. Note that GPSCOM may provide a better alignment to the International Terrestrial Reference Frame (ITRF) and can potentially solve for more sources of error in the GPS network solutions compared to ADJUST, although these solutions might not have an ideal alignment with the latest realization of the NSRS reference frame.

Regardless of the pathway chosen, the resulting solution reports contain coordinates for the observed user marks 1 as well as Continuously Operating GNSS Reference Stations, or CORSs 2, included in the project’s processing. These coordinates are reported in the current geometric (aka “horizontal”) datum realization of the National Spatial Reference System (NSRS), as well as the ITRF.

Tip

Throughout the manual, “CORS” or the plural “CORSs” is meant to refer to continuously operating GNSS reference stations in the NOAA CORS Network (NCN) and/or the International GNSS Service (IGS) network.

Conceptual diagram of OPUS Projects workflow

Fig. 1.2 Conceptual diagram of OPUS Projects workflow

OP was created to provide users with NSRS three-dimensional coordinate results for GNSS networks and a relatively easy route for submission to NGS. In the future, a much more expansive OPUS suite of tools will enable the simultaneous processing and adjustment of a variety of geodetic survey data, including additional types of GNSS data (e.g. real time kinematic vectors), leveling, distances and angles. This will fully support the new NSRS geospatial database and the new terrestrial reference frames and geopotential datum of 2022.

Footnotes:

1

Throughout the manual, the term “user mark” refers to a mark whose GNSS observations have been brought into the project by the user through the OPUS upload page. See Glossary for more information.

2

OPUS Projects accesses active GNSS control from the NOAA CORS Network (NCN) in addition to certain IGS stations which are not part of the NCN. For simplicity, this manual refers to them both as “CORS” (singular)) or “CORSs” (plural).