Explanation of descriptions in region files 

Target files are RS_latest.txt, spotYYYYMMDD.txt and spotgroupYYYYMMDD.txt (YYYY for year, MM for month, DD for day).
In this document, "*" is an alternative to the multiplication symbol. 

P: The apparent inclination of the solar axis [degree unit].
B0: The latitude on the center of solar disk [degree unit].
L0: The Carrington longitude on the center of solar disk [degree unit].
Radius: Radius of the Sun [arcsecond unit].
Obs radius: Observed radius of the Sun on a CCD [pixel unit].
RMS: The standard deviation of the solar disk's brightness derived from a FITS sdYYYYMMDD.fts (#1) [10^(-4)*I_c (#2) unit].
North: Northern hemisphere of the Sun.
South: Southern hemisphere of the Sun.
Whole: Whole disk of the Sun.
Center: Central region (A region within a circle whose center is the center of the projected solar disk and whose radius is a half of the solar radius).

--- Observed Sunspot Parameters ---

No.: ID number of an individual sunspot (#3) in an observation.
position: Position of the center of an individual sunspot [the latitude "Lat" (N, S) and the deviation of longitude from the central meridian "Lon" (E, W). degree unit].
cos(t): Cosine at the deviation angle  "t" from the center.
ap_area: Apparent area of an individual sunspot [no correction of the projection effect. MSH (#4) unit].
co_area: Area of an individual sunspot with the correction of projection effect [MSH unit].
darkness: Darkness of an individual sunspot [-10^(-2)*I_c unit] (#5).
Group id: ID number of a sunspot group to which an individual sunspot belongs (same as "No." in Observed Group Parameters).

--- Observed Group Parameters ---
No.: ID number of a sunspot group in an observation.
position: Position for the representative point of a sunspot group (#6) [the latitude (N, S) and the deviation of longitude from the central meridian (E, W). degree unit]. 
Carr. Lon.: Carrington longitude for the representative point of a sunspot group [degree unit].
f: Number of individual sunspots belonging a sunspot group. 
center: It indicates whether an sunspot group is in the central region or not. 1 if it is in the region, 0 if it is outside the region.

--- Relative Sunspot Numbers ---
g: Number of sunspot groups.
f: Number of individual sunspots.
10*g + f: Relative sunspot number with the correction factor k = 1. 
Seeing: Solar image quality considering atmospheric fluctuations and transparency [on a scale of 1 (worst) to 5 (excellent)].

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(#1) sdYYYYMMDD.fts: FITS image datum normalized by the brightness around the center of the solar disk with the limb darkening correction.

(#2) I_c: The brightness per pixel of the quiet region near the center of the solar disk. 

(#3) Indivisual sunspot: 
Individual sunspots are detected based on the criterion that the brightness of two or more neighboring pixels on the CCD falls below a threshold value. Threshold values for the sunspot detection are defined as follows: 

Penumbra: mi - (6.0*sd) ---(a),
Umbra: mi - (30.0*sd) ---(b), 

where, "mi" and "sd" are the mean and standard deviation (same as RMS) of brightness derived from the sdYYYYMMDD.fts, respectively. All features satisfying the threshold (a) are detected as individual sunspots, and dark spots that meet the threshold (b) are duplicated in counting. Therefore, f = 1 for a sunspot satisfying only (a), and f = 2 for a sunspot containing a dark patch satisfying (b) within penumbra.

Parameters with no-indication are for an individual sunspot that satisfy the sunspot detection threshold (a), and those for "Umbra only" are for a dark area that meet the sunspot detection threshold (b).

(#4) MSH: A millionth of the solar hemisphere (unit of sunspot area).

(#5) Darkness: The darkness of a sunspot is expressed as the decrease of brightness from a quiet region with the same apparent area and position as the individual sunspot. When the sunspot has the total brightness X and the area of the quiet region has the total brightness I, 

darkness = {X - I}/{-10^(-2)*I_c }.

(#6) The representative point of a sunspot group: 
It is calculated by averaging the midpoint [LatC, LonC] and the barycenter [LatB, LonB] of a sunspot group, i.e. 

[(LatC + LatB)/2, (LonC + LonB)/2]. 

The sunspot group's midpoint is calculated by 

[LatC, LonC] = [(LatN + LatS)/2, (LonE + LonW)/2] 

using the latitude values (LatN, LatS) for the northernmost and southernmost sunspots and the values of the longitudinal deviation from the central meridian (LonE, LonW) for the easternmost and westernmost sunspots in the sunspot group. The barycenter is calculated as 

[LatB, LonB] = [(w1*Lat1 + ... + wi*Lati + ... + wn*RLatn)/n, (w1*Lon1 + ... + wi*Loni + ... + wn*Lonn)/n], 

where "wi" and [Lati, Loni] are a weighting factor [equal to the square root of the area with the projection effect correction (~diameter)] and the position of the i-th sunspot, for all the n individual sunspots in the group. The above method is set up to reproduce the determination of the barycenter of sunspot group by an expert of the solar observation and is used to determine the sunspot group inside the central region.