#### Coordinate system

The coordinate system of the data is the Finland Uniform Coordinate System (EPSG:2393). This is a projected coordinate reference system based on the Hayford ellipsoid (1924) and transverse Mercator projection, with the central meridian set along the 27th meridian east. This one grid zone covers the whole of Finland.

In Finnish, the coordinate system is known either as "Yhtenäiskoordinaattijärjestelmä" (YKJ) or "Kartastokoordinaattijärjestelmä, kaista 3" (KKJ3). These two abbreviations are occasionally used in OpenFIRE data files.

The false easting of the reference system is Y = 3 500 000 meters.

Common mid-point coordinates are also available in alternative geographical coordinates, located on the EUREF-FIN (ETRS89) datum.

#### Syntax of pole coordinate files

The coordinate units are in meters. As a convention, the X (bytes 73–76 or 81–84) in trace headers is the **northing** and Y (bytes 77–80 or 85–88) is the **easting**. Comment lines start with the symbol #, followed by the coordinates of each peg.

The coordinate files have 3 columns, from left to right POLEID (pole identifier number), X (northing in meters) and Y (easting in meters). The pole coordinates are given for each subdivision of line separately.

**An example:**

# Pole coordinates for FIRE 3-1.

# Units are in metres. Coordinate system KKJ3.

# Format string: "%6d %11d %11d\n"

#

# Fire 3-1 starts here

# POLEID X(NORTHING) Y(EASTING)

1 6975392 3591999

2 6975408 3592046

3 6975428 3592092

4 6975448 3592138

#### Syntax of CMP coordinate files

The coordinate units in stacked data are in meters. As a convention, the X (bytes 73–76 or 81–84) in trace headers is the **northing** and Y (bytes 77–80 or 85–88) is the **easting**. Comment lines start with the symbol #, followed by the coordinates of each common mid-point.

The coordinate files have 3 columns, from left to right CMPID (common mid-point identifier number), X (northing in meters) and Y (easting in meters). The CMP coordinates are given for each subdivision of line separately.

**An example:**

# CMP coordinates for FIRE 1-1.

# Units are in metres. Coordinate system KKJ3.

# Format string: "%6d %11d %11d\n"

#

# Fire 1-1 starts here

# CMPID X(NORTHING) Y(EASTING)

10 7162587 3641460

11 7162562 3641463

12 7162537 3641466

Alternatively, the coordinate columns can be LATITUDE and LONGITUDE, given in decimal degrees on the EUREF-FIN datum.

**An example:**

# CMP coordinates for FIRE 1-1.

# Units are in decimal degrees (EUREF-FIN).

# Format string: "%6d %10.6f %10.6f\n"

#

# Fire 1-1 starts here

# CMPID LATITUDE LONGITUDE

10 64.532124 29.944352

11 64.531899 29.944390

12 64.531674 29.944429