Simple Example

We take the following considerations as examples:

• Suppose that you want to check the observation ability of a given VLBI network and obtain the best time range of observations. Let's make it step by step via Command-Line interface.
• You also want to check the image noise, time or bandwidth smearing.

Task 1: observation survey

1 Prepare you configuration file

Firstly, create your own configuration file or modify the default file, config_obs.ini. Following info should be provided.

[obs_time] start = 2020/01/01/00/00/00 end = 2020/01/02/00/00/00 step = 00/00/05/00

[bs_type] bs_flag_gg = 1 bs_flag_gs = 0 bs_flag_ss = 0

[obs_mode] obs_freq = 1.63e9 bandwidth = 3.2e7 cutoff_angle = 10.0 precession_mode = 0 unit_flag = km

[station] pos_source = 0316+413 pos_vlbi = ShangHai, Tianma, Urumqi, GIFU11, HITACHI,KASHIM34 pos_telemetry = pos_satellite =

[imaging] n_pix = 512 source_model = Point-source.model clean_gain = 0.9 clean_threshold = 0.01 clean_niter = 20 color_map_name = hot

We recommend you use the default file when you try VNSIM for the first time.

2 Check the function you need

Go through the table listed at Home page, you can easily get what you need. Here, for instance, we need the script Func_obs.py. Then, go the home directory of VNSIM, and try it

$ python Func_obs.py -h

Following info will shows:

NOTE THAT: the configuration file must be put under the diretory ./CONFIG_FILE/, otherwise it won't work.

3 Run and save

With the help info, let's choose to show gui, set the output image in the png format, and show the best time range information. Just run,

$ python Func_obs.py -g -i -f png

and the following info will show firstly,

shaos-iMac-7980:VNSIM shao$ python Func_obs.py -g -i -f png
optimal observation interval is : (6.6666666604578495, 18.833333315793425)
Best Obs: from 2020/1/1 6:40:0 to 2020/1/1 18:50:0

and there will also be two pictures poping out,

And the generated images are also save under the ./OUTPUT/obs_ability/ automatically.

PS. What does the picture mean? Please check more on User Guide, or our paper

Task 2: parameter calculation

To calcualte some parameters, just run the Func_cal.py scripts,

$ python Func_cal.py -h

you will see

usage: Func_cal.py [-h] [-g] [-i]

Run Parameter Evaluation

optional arguments:
  -h, --help       show this help message and exit
  -g, --show_gui   Choose to use my developed parameter calculators
  -i, --show_info  Show info about our design

You can check more design info by adding the auguments -i. Here we run it directly with GUI,

$ python Func_cal.py -g

Then,