Internal APM format

The APM internal storage format consists of files with the followiing format:

• 2 Header records of 576 bytes
• Data records are 576 bytes per record with 24 objects per record and 24 bytes per object
• the 24 bytes descriptions of each object are described in the table below

 

Table: Description of APM internal data format

Bytes	Format	Description
1-4	R*4	x coordinate in APM pixels
5-8	R*4	y coordinate in APM pixels
9-10	I*2	E plate magnitude*1000
11-12	I*2	E plate image classification
13	I*1	E plate PA
14	I*1	E plate eccentricity
15-16	I*2	E plate isophotal size
17-18	I*2	O plate magnitude*1000
19-20	I*2	O plate image classification
21-22	I*1	O plate PA
23-23	I*1	O plate eccentricity
24-24	I*2	O plate isophotal size

Notes on the APM parameters

Notes of magnitudes
Internally the magnitudes are stored at I*2, to convert to original
uncalibrated magnitudes, one must multiple by 1000.

Notes O and E plate magnitudes
set to -1 if the object is absent becuase of a plate edge limit

Notes on image classification

ICLASS=NINT((7500.0+IC)/15000.0)

CLASS_SIGMA=(I2_3-IC*15000+7500)/75.0


Notes on ellipticity
ELLIPT=(IVAL)+128)/255.0

Notes on PA
TBD

Notes on Major axis size 
TBD