GLF (Gemini Log Format) Data Reference

Overview

The Gemini SDK uses GLF (Gemini Log Format) to deliver processed, beamformed sonar images via the Svs5Sequencer API.

Key GLF Structure

GLF::GLogTargetImage
├── GLF::GMainImage m_mainImage
│   ├── std::vector<UInt8>* m_vecData (intensity values, beam-major order)
│   ├── std::vector<double>* m_vecBearingTable (beam angles in radians)
│   ├── UInt32 m_uiStartRange / m_uiEndRange
│   ├── UInt32 m_uiModulationFrequency (Hz)
│   ├── float m_fSosAtXd (sound speed)
│   ├── Int16 m_sPercentGain
│   ├── double m_dbTxTime (timestamp)
│   └── UInt8 m_ucPlatform (sonar model ID)
└── GLF::GZoomImage m_aczImage (optional acoustic zoom)

Data Layout

Image data in m_vecData is organized in beam-major order:

[beam0_samples, beam1_samples, ..., beamN_samples]

Calculate dimensions:

num_beams = m_vecBearingTable->size()
samples_per_beam = m_vecData->size() / num_beams

Access specific sample:

index = beam_idx * samples_per_beam + sample_idx
intensity = (*m_vecData)[index]

Essential Metadata Fields

Field	Type	Description
m_vecBearingTable	vector<double>	Beam angles in radians
m_uiModulationFrequency	UInt32	Operating frequency (Hz)
m_fSosAtXd	float	Sound speed (m/s)
m_sPercentGain	Int16	Receiver gain (0-100%)
m_dbTxTime	double	Transmit timestamp
m_ucPlatform	UInt8	Sonar model (4 = Gemini 1200ik)

Usage Example

// Receive and parse GLF message
GLF::GLogTargetImage* image = (GLF::GLogTargetImage*)value;
const GLF::GMainImage& mainImage = image->m_mainImage;
 
// Extract dimensions
size_t num_beams = mainImage.m_vecBearingTable->size();
size_t samples_per_beam = mainImage.m_vecData->size() / num_beams;
 
// Access beam data
for (size_t beam = 0; beam < num_beams; ++beam) {
    double angle = (*mainImage.m_vecBearingTable)[beam];
    for (size_t sample = 0; sample < samples_per_beam; ++sample) {
        size_t idx = beam * samples_per_beam + sample;
        uint8_t intensity = (*mainImage.m_vecData)[idx];
    }
}

References

• GLF Structure: GenesisSerializer/GlfLoggerGeminiStructure.h
• SDK API: Svs5Seq/Svs5SequencerApi.h