General Characteristics of ATIS

It is assumed that ATIS will exist as files in computers associated with the PA and with the telescope. These could be in the same computer, but usually are not. ATIS does not define how the information in these files is transferred between the computers. ATIS could be implemented with the transfers taking place manually by moving files on disks or tape through the mail. More typically, the transfer of data will be through data communication links by dial modem or wide area networks such as the Internet.

There are generally four kinds of ATIS files as shown in this diagram:

ATIS is the general term for all four file types described below:

ATIS input files have the following structure:

Header
Statements about date, Site, Telescope or Instrument
Advice

A linked list of statements of group selection criteria based on time dependent or certain testable conditions. Advice statements are optional and normally generated by automatic schedulers.
Group
Sequences of logically related statements consisting of :
  Headers - Group selection criteria and sorting information.
  Controls - Statements which cause actions in telescope or instrument.
  Comments - Generated by P.A.
  End of Group - An end of group marker.
End of File
  

 

ATIS output files have the following structure:
Header
 Statements about date, site, telescope or instrument.
Group
 Sequences of logically related statements consisting of:
  Headers - Group identification and sorting information
  Controls - Statements about th eactions preformed by the telescope or instrument
  Comments - Generated by the P.A. or telescope controller
  Results - Data and pointers to data files
End of File
  
   

Two optional temporary files are defined which are to be used only to monitor or modify an ATIS file on a particular night. These temporary files are called partial input and partial output files. These files are simply portions of an ATIS Input and Output file which are transmitted separately from the main files.

FITS Files

The data for simple detectors is contained in the ATIS output file itself. Additional auxiliary files are used to carry output data from multi-element detectors such as CCDs. These files use the "Flexible Image Transport System" (FITS) format for the storage. ATIS input statements request the generation of these files and the ATIS output statements carry information on the sequence of events related to the generation of these files.

File Name Conventions

The following file naming conventions are recommended but not required by ATIS. These names are acceptable to a wide variety of computers and allow the telescopes and the reduction programs to recognize and sort files. All information used in the file name is also carried in the file data itself, so the file names are for convenience only.

Defined file names are:

 
 
PAC to Telescope
Telescope to PAC
ATIS File
INNJJJJJ
ANNJJJJJ
Partial Files
RJJJJJXX
GJJJJJXX
Where
NN
= Telescope Number
 
JJJJJ
= Last 5 digits of JD
 
XX
= A two letter sequence AA AB

Additional rules for FITS files naming conventions are found at the beginning of the 500 series statements. The following rules are assumed for the use of these files.

ATIS Input Files (Required)

A telescope controller is expected to check for the presence of a file named INNJJJJJ at periodic intervals. The period is not specified in ATIS but would typically be at the beginning of the observing period for simple systems and after each group for networked telescopes. If a file exists with JJJJJ as defined in the 101 statement below, it will replace the current file in the telescope controller. If no file exists at the beginning of the observing period with a matching JJJJJ and an input file with the name INN00000 exists it will be executed. Input files with JJJJJ not equal to 00000 are will not be accessed again after they are loaded for execution allowing new files with a current JJJJJ to be transmitted during the night to replace an existing file. Archives of ATIS input files will typically be kept only by the PA if at all. New files with the name INN00000 transmitted during an observing night will not be executed until the next observing period.

ATIS Output Files (Required)

The ATIS output file is generated during the actual observing period. One telescope will generate only one ATIS output file per 24 hour period and it will carry the JJJJJ number of the date on which the file was created. How frequently ATIS output files are updated or partial ATIS files are transmitted to the PA is not defined. The ATIS output file could be communicated to the PA character by character in real time or many nights of ATIS files could accumulate before transmission takes place. The mechanism for the transmission is not defined by ATIS. These files are expected to be a permanent record of the raw scientific data and should only carry information which may be of scientific interest in the understanding of the results. Diagnostic information, if provided, should be carried in auxiliary files which are not presently defined by ATIS. Archiving by the PA and at least temporarily by the telescope controller is recommended. The user is ultimately responsible for the proper archiving of the results.

Partial Input Files (Optional)

Partial input files are temporary files which allow modification of an ATIS input file during its execution. They consist of either complete groups or advice statements. The JJJJJ must match the file being currently executed and they must be 'installed' in the telescope controller in sequential order. The frequency of transmission of these files is not defined by ATIS.

Partial Output Files (Optional)

Partial output files help provide a mechanism for implementing quasi real-time interaction between the PA and the telescope when continuous communication channels are not available. When implemented, the telescope generates partial files in addition to the normal ATIS output file. The data in each file would typically be one group but this is not an ATIS requirement. It is required that when all of the partial groups are concatenated in sequence, the complete ATIS output file is reproduced. When continuous communications channels are available, partial output files are unnecessary as the ATIS output file may be transmitted character by character or line by line to the PA.

FITS Files (Again)

When the data generated by automatic telescopes would be unwieldy to include in the ATIS output, or where ASCII text is unsuitable to carry the information, the standard is to utilize a FITS file to store the data. FITS format is defined elsewhere. ATIS does not define when or how these files will be transmitted to the PA but carries pointers in the form of filenames to the existence of the FITS files.

Structure of an ATIS File

ATIS files consist of statements consisting of lines of ASCII characters. Lines consist of space delimited parameters. Each line is terminated in an end of line character or characters which is not defined by ATIS except to state that the end of line character should be native to the computer in which the file resides. Translation of files to this native state should always be the responsibility of the receiving computer. Many file communication protocols do this translation automatically. File compression may also be used, but this is not defined by ATIS. ATIS defines four parameter types. They are integer, real, string, and text.

INTEGERS are whole decimal numbers whose range is appropriate for the parameter being measured. They may be negative where appropriate. Zero is recommended for dummy integer parameters. In handling negative declinations in a form commonly used by the astronomical community, the integer "-0" carries information and is different from the integer "0". For example, a declination or latitude of "-0 0 29" should be considered a valid input in ATIS93 and should be correctly interpreted. Software will probably handle the "integer" parameters as string characters, but that is up to the person writing the software.

REAL numbers are decimal numbers with a decimal fraction. They are required to have a numeric character before and after a decimal point. They may be negative. The precision should always be reasonable for the particular parameter. Exponential notation is not allowed. Recommended dummy values are 0.0 and 99.9 selected to minimize confusion.

STRINGS are defined as a series of up to 20 printable ASCII characters. A space is NOT acceptable within an ATIS STRING parameter as it is the parameter delimiter. It is general practice to use an underscore character "_" to represent a space within an ATIS STRING. A single underscore is recommended as the dummy or null parameter.

TEXT is also a series of ASCII characters. It differs from type STRING in that it may have any number of characters (while not violating the total line length requirements). There can be only one TEXT parameter on a line and it must be the last parameter of the line. The TEXT parameter is considered to contain all remaining characters on the line up to the end of line character(s). Zero characters is used as a dummy or null parameter. A TEXT parameter can be thought of as an undefined number of STRING parameters.

All ATIS parameters should follow these two simple guidelines:

All devices which generate ATIS parameters should restrict the range and precision of each parameter to meaningful values and should adhere closely to the format specifications.

All devices which receive ATIS parameters should be made robust such that errors in the file will not result in system failure and should be generous in the acceptable ranges for parameters.

ATIS Statements

Every ATIS statement is made up of one identifier line and zero or one information lines.

Identifier lines always consist of a single integer in the range of 100 to 999 followed by an end of line delimiter. The integer will indicate whether there will be an information line following.

Information lines have a variable number of parameters and variable length. The parameter format is determined by the preceding identifer line. Information lines always have 80 or less characters not including the end of line delimiter. The existence of a particular parameter may be optional but where an optional parameter exists, all preceding parameters must be present. The meaning of a parameter may also be variable but the meaning can always be determined from previous parameters within the same line.

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