B L O C K :

This Command is used to divide an adjustment into two blocks. The first block is defined by a polygon and will contain all the data originating from a station lying within the polygon. The second block contains all the rest of the data.

The vertices of the polygon are defined by a series of coordinates, entered in counter clockwise order. The minimum number is two which will define a rectangle with the four corners defined by the minimum and maximum latitude and longitude entered.

The procedure can be executed from GHOST either interactively or batch. For the batch mode a file is created and submitted to the batch queue. The user is queried for the polygon and subdirectories.

The user is queried for a data file or files to block. The procedure will loop and ask for files until a <CR> is encountered. At that stage the data will be divided into two blocks. The user is queried for a subdirectory to store block 1 and block 2. If the sub-directory does not exist, one will be created. Also, if the user does not want to store the data, a <CR> will exit the procedure.

The parent sub_directory will now be ready to initialize the ADJSUMY, STADATA and NUISPAR files using programs READCC and EDTPOS.

The original data file must contain enough data to completely define the interior block as well as any junctions from outside the data. The program recognizes a code 5 or 6 as defining an exterior junction block. These exterior points are maintained as junctions (code 5 or 6) in any block that contains data for the junction.

For each sibling block, code 4 stations are changed to code 5 to define the station as a junction between the blocks. These code 4 as well as any code 5 or 6 are stored in the parent BLKCORD file

The directory will contain the following data.

1. Coordinates : This file will contain a coordinate record for each station. The code for the stations will normally be 4, however if the station has data coming from another source or another block, that will be used in the adjustment it will be code 5 or code 6. Auxiliary parameters are stored as code 94 unless they are used in another block in which case they are code 8.
2. Observations : This file will contain all the observations defined as within the block. Observations are defined as within the block if the first station in the set is inside the polygon otherwise it is in the other block.

The program creates the folowing files from the original.

1. BLKPAR : A file of coordinates containing all the stations originally tagged as junctions (5,6) and all the stations determined by the program as junctions in the sibling blocks (tagged 4).
2. BLOCK1 : A file of coordinates containing all the stations determined by the program as within the defined polygon, as well as any stations directly connected outside the polygon by observations defined within the polygon. All the originally tagged code 5,6 records remain as long as there are observations within the polygon with that station. Any other station, within the polygon, which has an observation from outside the polygon will be a code 5. The station outside the polygon will only be retained in the other file as a code 5 if there are observations from outside.
3. BLOCK2 : A file of coordinates containing all the stations falling outside the polygon as well as any station within the polygon with an observation to a station outside the polygon. Both stations are saved with a code of 5.
4. OBS1 : A file of observations where the originating station lies within the polygon. For terrestrial observations this would be the first station on the record. For groups of stations, e.g. position observations, the originating station is the first station in the group.
5. OBS2 : A file of observations containing all the records with a definable code and which do not fall in the OBS1 file.
6. undef : A file of the coordinates or observations that do not fit within either block. For example a coordinate without any data associated with it or an obsevation with a corresponding coordinate.

With the VAX directory system a user could store the original data file as well as the BLKPAR file in the current sub-directory and establish two sub- directories. One subdirectory would be used to store the BLOCK1 and OBS1 files and the other to store the BLOCK2 and OBS2 files.

If the process has to be repeated to get a satisfactory size of block, the OBS1 file must be appended to the BLOCK1 file to create the input COMPILE data file.

                    Sudbury

              Block12       Block34

        Block1   Block2   Block3   Block4


         Interactive example:

SD @                                 <== Set directory to user root
SD .data.sudbury                     <== Enter the data directory
GHOST                                <== Make ghost interactive
BLOCK                                <== Execute the blocking procedure
$ File for Blocking ? Sudbury        <== User enters file
$ File for Blocking ? <CR>     <== File complete



$ Sub-directory for block1 ? Block12 <== Enter directory
$ Sub-directory for block2 ? Block34 <== Enter directory
sd .block12                          <== Divide next level
BLOCK
$ File for Blocking ? blkcord        <== User enters file
$ File for Blocking ? intcobs        <== User enters file
$ File for Blocking ? <CR>     <== file complete
 Enter polygon definition
 45,90
 47,91
 999,999
$ Sub-directory for block1 ? Block1  <== Enter directory
$ Sub-directory for block2 ? Block2  <== Enter directory
sd [-.block34]                       <== Divide next level
$ File for Blocking ? Blkcord        < User enters file
$ File for Blocking ? Intcobs        <== User enters file
$ File for Blocking ? <CR>     <== File complete
 Enter polygon definition
46,90.30
45,90
999,999
$ Sub-directory for block1 ? Block3  <== Enter directory
$ Sub-directory for block2 ? Block4  <== Enter directory

              The user is queried for data files
              The required files are appended until
              a <CR> is detected. The user is then
              queried for the polygon defining the block.
              When complete the user is queried for a
              subdirectory to store the two blocks.
              The procedure may be cycled until the
              appropriate file size is obtained.

 END ...