User`s guide

Y-axis Values

A trace’s Y-axis values are always stored in an SDF file’s Y-axis Data record. And when the file defines

a single trace, that record includes just one vector of Y-axis values. Reading this vector of values is

similar to reading a vector of X-axis values from the X-axis Data record.

Four fields in the Data Header record tell you how to read Y-axis values from the Y-axis Data record:

num_of_points: tells you how many discrete points the trace is composed of.

ydata_type: tells you the size and format of each Y-axis value. (This information is encoded.

For example, if ydata_type = 3, the size is our bytes and the format is binary

floating-point.)

yPerPoint:

tells you how many Y-axis values are used to define a single point.

yIsComplex: tells you whether each Y-axis value is purely real, or whether it consists of a real

and an imaginary component.

You can determine the size (in bytes) of the Y-axis Data record’s data block with the

following formula:

num_of_points  yPerPoint  Size  2

(yIsComplex)

The value of “Size” is encoded in ydata_type, as shown below:

ydata_type Size (bytes)

2,3 4

Standard Data Format (SDF)

B-29