BYN - Natural Resources Canada's Geoid

# BYN - Natural Resources Canada's Geoid file format (.byn)

Files with extension ".byn" have a binary format. The format includes two sections which are the Header and the Data. The data are stored by rows starting from the north. Each row is stored from the west to the east. The data are either short (2 bytes) or standard (4 bytes) integers. The size of the bytes is defined in the header.

The total size of the file is 80 bytes + (Row x Column x (2 or 4) bytes) where Row is the number of rows in the grid and Column is the number of columns in the grid. Row and Column can be calculated by these two equations:

Row = (North Boundary - South Boundary) / (NS Spacing) + 1

Column = (East Boundary - West Boundary) / (EW Spacing) + 1

The ".byn" files may contain undefined data. Depending if the data are stored as 2-byte or 4-byte integers, the undefined data are expressed the following way:

4-byte data (Standard integer): 9999.0 * Factor, the Factor is given in the header

2 byte data (Short integer): 32767

Most of the parameters in the ".byn" header can be read by clicking the “Information” icon in software GPS-H.

NOTE: Files with extension ".err" are also in the ".byn" format. An ".err" file usually contains the error estimates of the ".byn" file of the same name (e.g., CGG2013n83.byn and CGG2013n83.err). The ".err" file will have variable Data equal to 1 or 3.

### Factor

When translating from or into BYN file to or from another formats the scale will afect the result profundly.

Translating to a format that supports Scale (GTIFF for example) will mantain the data type and thescale information. The pixel values are perfectly preserved.

Translating to a format that does not support Scale will maintain the data type but without the Scale, meaning loss of information on every pixels.

The solution to the problem above is to use "-unscale" and "-ot Float32" when using gdal_translate or GDAL API. That will produce a dataset without scale but with the correct pixel information. Ex.:

gdal_translate CGG2013an83.err test2.tif -unscale -ot Float32

NOTE: The BYN header variable Factor is the inverse of GDAL Scale. (Scale = 1.0 / Factor).

## See Also:

- Implemented as `gdal/frmts/raw/byndataset.{h,cpp}`.
- www.nrcan.gc.ca