Snapspec is used to compute station coordinate orders based upon their relative and absolue accuracies. It uses statistical information generated by snap in conjunction with a configuration file defining the required accuracies for various orders of coordinates. It then attempts to assign optimal orders to coordinates such that the specifications are met.
This program servers a similar function to the snap test_specification command. The main difference is that whereas the test_specification command checks that a defined group of stations meets an accuracy specification, the snapspec program tries to work out which stations could meet specifications. The method it uses to do this attempts to choose stations meeting the specification in a way which that gets the most stations meeting the specification.
The program uses the same algorithm as used in Landonline to attribute orders to stations (though unlike Landonline it may test both horizontal and vertical accuracies).
Note that the SNAP adjustment program can test horizontal and vertical accuracy specifications for coordinates, but it cannot select whichs stations to assign orders to.
Snapspec is a command line utility run from a DOS prompt. The syntax for the command is:
snapspec [options] binary_file [config_file] listing_file
where:
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binary_file |
is the name of the binary file generated by snap. This is the same as the name of the snap command file, but with extension .bin. Note that the adjustment used to create the binary file must include the "output_decomposition" or "output all_relative_covariances" option in order for snapspec to be able to use it. |
|
config_file |
is an optional parameter specifying the name of the configuration file defining the specifications for each coordinate order. By default snapspec uses a file called snapspec.cfg in the same directory as the snapspec program. |
|
listing_file |
is the name of the listing file to generate which will specify the calculated coordinate orders. |
Snapspec can take the following options:
|
-o order |
Specifies the highest order to use in the tests. For example specifying -o 4 will assign orders 4 and below to stations, but not 1, 2, or 3. Generally this should be an order lower than the lowest order of fixed station in the adjustment (so if order 1-4 stations are held fixed, then snapspec should be run with -o 5. |
|
-a |
Instructs snapspec to determine the highest order to assign in the tests based upon the orders of the fixed stations controlling the adjustment. Snapspec will determine the lowest order of fixed station and only assign lower orders to adjusted stations. This requires that the coordinate file used for the SNAP adjustment has station orders, and that all the coordinate orders of fixed stations are defined in the snapspec configuration file. |
|
-m mode |
where mode can be one of "auto" (default), "horizontal", "vertical", or "3d". The configuration may define both horizontal and vertical relative accuracy tests. The mode determines which are applied. By default snapspec examines the adjustment and chooses the mode based on which coordinates (horizontal and/or vertical) are calculated, and what tests are defined in the configuration file. |
|
-c filename |
Specifies the name of an output CSV file containing the snapspec results. |
|
-u filename |
Specifies the name of an output coordinate file containing the station coordinates and updated orders. |
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-f filename |
specifies that the program should generate a separate file of stations coordinates for each order calculated. The filename should not include an extension .. the program will append the order and extension to this name for each file generated. |
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-v |
Causes snapspec to create a cache file containing calculated covariance information. This will only happen if snapspec is using the normal equation decomposition matrix and if it uses this to calculate the inverse. In this case with the -c option it will save the calculated inverse in a file with the same name as the binary file but extension ".scc". When snapspec runs it always checks for a cache file. The cache uses the adjustment run time to confirm that the cache file is still current. |
For the -c, -u, and -f options the filename can be entered as "-", in which case a default filename will be used based on the name of the snap binary file.