Before You Generate a Mosaic

Use this when

You are about to generate a mosaic and want to know whether your recording is likely to produce a good result.

What your recording needs

Side Imaging channels. The mosaic pipeline uses port and starboard Side Imaging data. A recording without both channels cannot produce a mosaic. If the Side Imaging tab is missing in the viewer, the file does not contain that data.

GPS coverage throughout the survey. HumVision derives the geographic position of each sonar ping from the GPS coordinates stored in the recording. Pings with no GPS fix (latitude and longitude both zero, or missing entirely) are skipped. If most of the recording has no GPS data, the mosaic will fail with "Not enough GPS extent to build a mosaic."

Minimum boat speed. Pings recorded while the boat is moving slower than about 0.9 knots are skipped. At very low speeds, course-over-ground from GPS is too noisy to determine a reliable heading, and painting those pings produces starburst artifacts. A recording captured mostly while drifting or idling will have few usable pings.

Quick checks

• Open the recording in HumVision and switch to the Side Imaging view. If you see sonar data on both sides of the nadir line, the channels are present.
• Switch to the Map tab. If a GPS track appears, GPS data is present.
• Review the track length. A longer, straighter track with consistent boat speed tends to produce the clearest mosaics.

What will produce a poor mosaic

• Very low speed throughout — the mosaic may still generate but will show a warning: "Best-effort mosaic: this recording was captured at very low speed, so heading/course-over-ground is unstable and the mosaic may smear or streak."
• Tight turns — sharp heading changes between pings can cause streaks. The pipeline skips pings where heading jumps more than 12 degrees between consecutive samples.
• Interrupted GPS — sections with GPS dropout will have gaps in the mosaic.
• Very large survey area at high resolution — the pipeline caps total pixels at 50 million. If your chosen resolution would exceed that limit, the pipeline automatically reduces resolution until the mosaic fits. You will see the actual meters-per-pixel in the status bar after generation.