OPUS FAILURE – GNSS FIELD DECISION CHART
Printable 1‑Page Reference for Professional Land Surveyors
START: OPUS unavailable or OPUS solution failed
1
DATA LENGTH CHECK
Do you have ≥ 2 HOURS of clean static GNSS data?
YES → Go to 2
NO → Can you re‑observe?
YES → Re‑observe ≥ 2 hrs, then restart
NO → Go to 5 (Real‑Time Options)
2
CORS AVAILABILITY
Are there ≥ 3 CORS within 70 km?
YES → Go to 3
NO → Go to 4 (PPP)
3
NETWORK‑BASED PROCESSING
3A. OPUS‑RS
• Min: 15 min (prefer ≥ 30 min)
• Expected Accuracy: H: 2–5 cm | V: 5–10 cm
• Expected Accuracy: H: 2–5 cm | V: 5–10 cm
SUCCESS → Go to 6 (QA)
FAIL → Try 3B
3B. MANUAL STATIC PROCESSING
• Download CORS RINEX (State DOT / NGS / RTN)
• Process in TBC / Infinity / MAGNET / RTKLIB
• Process in TBC / Infinity / MAGNET / RTKLIB
FIXED, GOOD RMS → Go to 6 (QA)
FAIL → Go to 4 (PPP)
4
PRECISE POINT POSITIONING (PPP)
(No base required)
Preferred Order:
1. CSRS‑PPP (Free, Global)
2. Trimble RTX (Post‑Processed)
3. JPL APPS / GAPS
1. CSRS‑PPP (Free, Global)
2. Trimble RTX (Post‑Processed)
3. JPL APPS / GAPS
Requirements: ≥ 1–2 hrs data | Dual‑frequency GNSS | Clear sky view
Expected Accuracy: H: 1–2 cm | V: 3–5 cm
Expected Accuracy: H: 1–2 cm | V: 3–5 cm
SUCCESS → Go to 6 (QA)
FAIL → Go to 5
5
REAL‑TIME FIELD CONTINUITY
5A. RTN / VRS Available?
• State RTN / SmartNet / VRS Now
• Verify datum, epoch, geoid
→ Use as TEMPORARY CONTROL
• Verify datum, epoch, geoid
→ Use as TEMPORARY CONTROL
5B. LOCAL BASE RTK
• Set base on published or prior OPUS control
• Observe ≥ 2 independent sessions
→ Post‑process later if required
• Observe ≥ 2 independent sessions
→ Post‑process later if required
Single RTK shot = NOT CONTROL
6
QUALITY ASSURANCE (REQUIRED)
✔ Compare 2 independent solutions
• Static vs PPP | PPP vs RTN | OPUS‑RS vs Static
• Static vs PPP | PPP vs RTN | OPUS‑RS vs Static
✔ Acceptance Checks:
• Horizontal ≤ 0.03 m | Vertical ≤ 0.05 m | Good repeatability
• Horizontal ≤ 0.03 m | Vertical ≤ 0.05 m | Good repeatability
✔ Document:
• Antenna model & height | Occupation time | Processing method | Datum realization
• Antenna model & height | Occupation time | Processing method | Datum realization
FINAL CONTROL CLASSIFICATION
| Method | Control Class |
|---|---|
| OPUS Static / Manual Static | Primary Control |
| PPP (CSRS / RTX) | Primary Control |
| OPUS‑RS | Secondary Control |
| RTN / Local RTK | Working Control |
FIELD RULE: When OPUS fails: longer observations + multiple solutions = defensible control.