The ‘FileType’ stored in the file header is “Sonagram”.
Header data
This file type uses the ‘File Header’ described in chapter File Header.
The following additional data is stored in the Header, following the default header:
Ø DocSizeX: the document width.
Ø DocSizeY: the document height.
Ø CursorA: the value of the cusorA.
Ø CursorB: the value of the cusorB.
Ø Bandwidth: the Bandwidth value.
Ø Offset (Translation): the Offset value.
Ø LowFreqLimit: the lower frequency limit value.
Ø HighFreqLimit: the higher frequency limit value.
Ø LowMagLimit: the lower magnitude limit value.
Ø HighMagLimit: the higher magnitude limit value.
Ø VideoFilterOn: the VideoFilter On/Off flag.
To the default file header with 64 bytes additional a block of 48 bytes is added.
The additional block contains display parameter used by the WAVECOM GUI for displaying the stored data correctly.
NOTE: the following struct type could be used to extract the data header.
struct SonagramData
{
long lDocSizeX;
long lDocSizeY;
double dCursorA;
double dCursorB;
long lBandwidth;
long lTranslation;
long lLowFrequencyLimit;
long lHighFrequencyLimit;
short sLowMagnitudeLimit;
short sHighMagnitudeLimit;
BOOL boVideoFilterOn;
};
Data
This ‘FileType’ uses the data structure described in chapter Data Structures to store the data.
The stored sonagram data has the following structure:
Ø FFT Samples: the first 4096 bytes of the stored data contain the 2048 sample values for the FFT.
Ø Time: the last 16 bite of the stored data contains the system time timestamp value of the received data( the additional timestamp is necessary because the default timestamp in the data header does not support milliseconds ). The TIME value is the the number of seconds elapsed since midnight (00:00:00), January 1, 1970, coordinated universal time, according to the system clock.
The data for the ‘Sonagram’ file types occupies 4112 bytes inside a data package after the data header.
A data package in the .WDA file contains the data points of one FFT sample and its timestamp value. The FFT sample data points are stored in short values(2-bit type), that is 2 Bytes in the .WDA file contains the value of one FFT sample data point.
NOTE: the following struct type could be used to extract the data.
typedef struct ST_SONAGRAM_DATA
{
short asFFTSamp[2048];
SYSTEMTIME Time;
} ST_SONAGRAM_DATA;