Never Stop Surveying: 5 GNSS Post-Processing Alternatives to OPUS Downtime

OPUS Is Down. Now What?

Five GNSS Post-Processing Options Every Professional Surveyor Should Already Have in Their Back Pocket

Introduction: When OPUS Goes Quiet

Most of us build OPUS into our daily production workflow because it’s free, it’s tied to the NSRS, and nine times out of ten it just works. The problem is that when it doesn’t—government shutdowns, server maintenance, traffic overload—the failure is absolute. Crews keep collecting data, but the office hits a wall. Deliverables stall, schedules slip, and you’re suddenly explaining to a client why “NOAA is down” is now their problem.

That’s not a technology problem; it’s a workflow problem. Any operation that depends on a single external processing service has a built-in single point of failure.

What follows are five GNSS post-processing alternatives that professional surveyors can use today to keep projects moving when OPUS is unavailable. Some are free, some are commercial, some require more technical effort—but every one of them is a legitimate, survey-grade solution if you understand what you’re doing.

OPUS Down- Alternatives

1. CSRS-PPP (Canada): Best-in-Class PPP, No Base Required

Natural Resources Canada’s CSRS-PPP is, hands down, one of the most reliable free PPP services available worldwide.

This is straight Precise Point Positioning using IGS precise orbit and clock products. No base station required, no reliance on nearby CORS, and no geographic limitation to Canada despite the name. Upload your RINEX, pick static or kinematic, single or dual frequency, and let it run.

From a performance standpoint, CSRS-PPP has repeatedly tested at or near the top in independent comparisons. Multiple studies—including CLGE and peer-reviewed academic analyses—have shown it to produce more consistent and repeatable results than most other online PPP engines.

Why surveyors should care:

  • Global coverage

  • No dependency on local CORS density

  • Excellent long-session static results

  • Clean reporting and transparent metadata

If OPUS is down and you’re sitting on multi-hour static occupations, CSRS-PPP is usually the first place I send people.

2. AUSPOS: Old-School Relative Positioning Done Right

AUSPOS, operated by Geoscience Australia, takes a very different approach—and for many surveyors, that’s a feature, not a bug.

This is relative positioning, not PPP. AUSPOS forms baselines from your submitted data to multiple high-quality IGS stations, then performs a network adjustment. Conceptually, it’s much closer to how most of us were trained to think about GNSS control.

Requirements are stricter:

  • Static, dual-frequency GPS

  • One hour minimum (six hours recommended)

  • Best results with long sessions (12–24 hours)

But the payoff is stability. Independent evaluations have consistently shown AUSPOS producing extremely reliable coordinates, often outperforming PPP services when long occupations are available.

Why surveyors should care:

  • True network-based solution

  • Tied directly to the IGS framework

  • Excellent for primary control and long-session work

If you’re comfortable thinking in baselines instead of black-box PPP, AUSPOS is a rock-solid OPUS substitute.

3. Trimble CenterPoint RTX: Commercial PPP Without the Hardware Lock-In

Trimble’s CenterPoint RTX post-processing service sits in the middle ground between government-run services and fully commercial workflows.

It’s a global PPP service, accessible through a free web portal, and it works with static data from non-Trimble receivers as well. If you’re already running Trimble Business Center or tools like LP360, the integration can streamline processing and coordinate management.

A couple of professional caveats:

  • Plan on longer occupations (one hour minimum is a practical baseline).

  • Be aware of reference frame transformations. The RTX web service uses the Morvel56 plate model for NAD83 transformations, while TBC can use HTDP. That matters for control work and multi-epoch consistency.

Why surveyors should care:

  • Backed by a major vendor

  • Global coverage

  • Clean workflow integration

  • Predictable performance

RTX won’t replace OPUS for every job, but it’s a very practical fallback—especially in Trimble-heavy shops.

4. RTKLIB: Full Control, Zero Cost, Steep Learning Curve

If you want maximum independence, RTKLIB is still the king of open-source GNSS post-processing.

This is not a web service. It’s a processing engine. You supply:

  • Your rover data

  • Base station RINEX (or PPP products)

  • Precise orbits and clocks

  • All the processing decisions OPUS hides from you

RTKLIB can do static, kinematic, relative, PPP, multi-constellation—you name it. The tradeoff is that you are responsible for configuration, quality control, and understanding what the software is actually doing.

Why surveyors should care:

  • Completely free

  • No external service dependency

  • Transparent algorithms

  • Highly customizable workflows

If you have someone in the office who truly understands GNSS, RTKLIB can keep you operational even when every online service is offline.

5. Your Own Base Station: Total Independence

The ultimate OPUS backup isn’t software—it’s infrastructure.

Running your own base station and post-processing your own baselines gives you full control over your workflow. No internet. No CORS availability issues. No third-party processing queues.

The model is straightforward:

  • Set a survey-grade receiver on known (or to-be-established) control

  • Log raw data continuously

  • Post-process against rover data in TBC, RTKLIB, or similar software

This approach shines in:

  • Remote areas

  • Sparse CORS regions

  • Critical control networks

  • Long-term or repeat monitoring projects

Yes, it requires more gear and more expertise. But from a risk-management standpoint, nothing beats it.

6. Common Causes of OPUS Failure (and Workarounds)

Issue Solution
Short occupation Use OPUS-RS or PPP
Sparse CORS Use PPP (CSRS-PPP / RTX)
Bad multipath Re-observe at different time
Antenna mismatch Manually process
Server outage Local processing or CSRS-PPP
Datum confusion RTN with known realization

 

7. Best-Practice Fallback Strategy (Field-Ready)

Recommended hierarchy:

  1. OPUS Static

  2. OPUS-RS

  3. CSRS-PPP

  4. Local CORS + TBC/Infinity

  5. RTX / SmartNet

  6. RTN / Local Base RTK

đź“Ś Always observe longer than minimums when OPUS is questionable

8. Professional Tip (Survey-Grade QA)

When OPUS is unavailable:

  • Observe ≥2 independent sessions

  • Use different time windows

  • Compare PPP vs Network solutions

  • Check:

    • RMS

    • Coordinate repeatability

    • Antenna metadata

 

Conclusion: Redundancy Is Professional Practice

OPUS is a fantastic tool—but building your entire GNSS workflow around a single service is a gamble, not a strategy.

Professional resilience comes from redundancy:

  • Knowing at least one PPP alternative

  • Understanding relative positioning services

  • Having in-house processing capability

  • Being able to fall back on your own hardware when needed

GNSS is moving toward hybrid models like PPP-RTK, but the fundamentals haven’t changed. Surveyors who understand both network-based and absolute positioning—and who can process data without leaning on a single button—are the ones who don’t lose production days when a server goes dark.

In this business, preparedness isn’t optional. It’s part of being a professional.