User`s guide

You can calculate X-axis values this way when xResolution_type is 1 (logarithmic resolution):
x0 = abscissa_firstX
x1 = x0 * abscissa_deltaX
x2 = x0 * abscissa_deltaX
2
x3 = x0 * abscissa_deltaX
3
.
.
.
xn = x0 * abscissa_deltaX
n
(where n = num_of_points −1)
When consecutive trace points are not evenly spaced along the X-axis (xResolution_type = 2, 3, or 4), the
SDF file includes an X-axis Data record. And when the file defines a single trace, that record includes
just one vector of X-axis values.
Three fields in the Data Header record tell you how to read X-axis values from the X-axis
Data record:
num_of_points: tells you how many discrete points the trace is composed of.
xdata_type: tells you the size and format of each X-axis value. (This information is encoded.
For example, if xdata_type = 3, the size is four bytes and the format is binary
floating-point.)
xPerPoint: tells you how many X-axis values are used to define a single point.
You can determine the size (in bytes) of the X-axis Data record’s data block with the
following formula:
num_of_points * xPerPoint * Size
The value of “Size” is encoded in xdata_type, as shown below:
xdata_type Size (bytes)
12
2,3 4
48
Standard Data Format (SDF)
B-28