# Extract A Radar Column Along a Line of Azimuth **URL:** \ **Category:** General\ **Tags:** py-art, data\ **Created:** [April 6, 2023, 9:38pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207 "2023-04-06T21:38:31Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 6, 2023, 9:38pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/1 "2023-04-06T21:38:31Z")
Using the attached figure as an example, I want to extract column data along a 242 degree azimuth black dotted line from radar (0 -125 km) volume PPI plot (0.8 deg elevation). The file is in NC format. How can I go about it using Py-ART? I’m aiming to plot these data (dBZ) against the radar range 125 km. ![example_plot_033412](https://global.discourse-cdn.com/free1/uploads/openradar/original/1X/14b825e3d056281968298456d6ef6fc417530c8e.jpeg) ---
**Author:** ![mgrover1](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/mgrover1/32/7_2.png) [@mgrover1](https://openradar.discourse.group/u/mgrover1)\ **Post date:** [April 7, 2023, 1:26pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/2 "2023-04-07T13:26:28Z")
Thanks for the question @Gitbix - I would suggest using [xradar](https://xradar.readthedocs.io/) here, which enables you to do this! Here is a sample code block, using some sample data. ```python import xradar as xd from open_radar_data import DATASETS # Load in a sample file from the Southern Great Plains ARM Site file = DATASETS.fetch('sample_sgp_data.nc') # Read the data using xradar dtree = xd.io.open_cfradial1_datatree( file, ) # Select the lowest sweep (0), and the closes azimuth to 242 degrees, and plot it! dtree['sweep_1'].sel(azimuth=242, method='nearest')['corrected_reflectivity_horizontal'].plot() ``` Here is the result (note, there are some missing values, and we did not explicitly interpolate): ![Screenshot 2023-04-07 at 8.22.55 AM](https://global.discourse-cdn.com/free1/uploads/openradar/original/1X/c764ceaa85a7be85f7175ee3cf60ad36401f9bb9.jpeg) ---
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 7, 2023, 5:29pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/3 "2023-04-07T17:29:10Z")
Hey, Thanks Max. I’d be using this xradar method for the first time. What if I want to plot only some dBZ data in a fixed range say between 40 to 50 Km and not all? ---
**Author:** ![mgrover1](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/mgrover1/32/7_2.png) [@mgrover1](https://openradar.discourse.group/u/mgrover1)\ **Post date:** [April 7, 2023, 5:53pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/4 "2023-04-07T17:53:30Z")
@Gitbix you could add another selection here (note range units are meters): ```python ds.sel(range=slice(40_000, 50_000)) ``` or the full line: ```python dtree['sweep_1'].sel(azimuth=242, method='nearest').sel(range=slice(40_000, 50_000))['corrected_reflectivity_horizontal'].plot() ``` ---
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 7, 2023, 6:01pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/5 "2023-04-07T18:01:16Z")
Thank you very much. ---
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 8, 2023, 8:41pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/6 "2023-04-08T20:41:38Z")
How can the dataset in ‘file’ be read with “dtree = xd.io.open\_cfradial1\_datatree(file)” if the dataset contains variable “nsweep” and not ‘sweep\_number’? Error from the line above is seen below. ![error](https://global.discourse-cdn.com/free1/uploads/openradar/original/1X/3befe12697f9871a88876edea7a0da2f009d2810.jpeg) ---
**Author:** ![mgrover1](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/mgrover1/32/7_2.png) [@mgrover1](https://openradar.discourse.group/u/mgrover1)\ **Post date:** [April 10, 2023, 4:21pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/7 "2023-04-10T16:21:36Z")
> [@Gitbix](#): > > “nsweep” and not ‘sweep\_num Are you sure the data you are reading is a cfradial file? Can you rename the variable using netCDF? The reader is assuming the cfradial1 standard, which uses the name `sweep_number`. ---
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 10, 2023, 4:58pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/8 "2023-04-10T16:58:58Z")
Yes, the data is a cfradial NC file having the variable sweep\_number. The version from metadata is CF-Radial 1.4. Also, I’m not sure the data type exist in the datasets module above. ![S_N](https://global.discourse-cdn.com/free1/uploads/openradar/original/1X/f08e26f3935f2dadb38fb7fa74d82a13311b2a22.jpeg) ---
**Author:** ![mgrover1](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/mgrover1/32/7_2.png) [@mgrover1](https://openradar.discourse.group/u/mgrover1)\ **Post date:** [April 10, 2023, 5:36pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/9 "2023-04-10T17:36:25Z")
Can you share a copy of the code block you are running? ---
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 10, 2023, 6:05pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/10 "2023-04-10T18:05:37Z")
Yes, here is it. Having installed and imported all modules. ![code](https://global.discourse-cdn.com/free1/uploads/openradar/original/1X/f67c7fa2b3cc44d0dd1467ebe818625dd27833c4.jpeg) ---
**Author:** ![mgrover1](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/mgrover1/32/7_2.png) [@mgrover1](https://openradar.discourse.group/u/mgrover1)\ **Post date:** [April 10, 2023, 8:12pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/11 "2023-04-10T20:12:13Z")
@Gitbix it looks like that file is missing sweep\_number still - using following fixes the read in, by adding a new `sweep_number` variable to the dataset using the existing `sweep` variable, writing to disk, then reading back in using `xradar` ```python # Open the original file ds = xr.open_dataset('cfrad.20211211_120304.494_to_20211211_120801.176_KBSI_SUR.nc') # Make sure that sweep number is one of the variables in the dataset ds['sweep_number'] = ds.sweep # Write this new netcdf file to disk ds.to_netcdf('cfrad.20211211_120304.494_to_20211211_120801.176_KBSI_SUR.nc',) # Read the data back in using xradar tree = xd.io.open_cfradial1_datatree('cfrad.20211211_120304.494_to_20211211_120801.176_KBSI_SUR.nc') ``` ---
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 10, 2023, 11:06pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/12 "2023-04-10T23:06:51Z")
Oh really. So, the solution is to ingest the sweep\_number variable into the same file? Would try check it out. Thank you. ---
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 10, 2023, 11:49pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/13 "2023-04-10T23:49:51Z")
I plotted the data but it seems to be empty. What could be wrong? ![data_plot](https://global.discourse-cdn.com/free1/uploads/openradar/original/1X/8e68fb1fa34dd0d19fefba5ebc97562419da4b78.png) ---
**Author:** ![mgrover1](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/mgrover1/32/7_2.png) [@mgrover1](https://openradar.discourse.group/u/mgrover1)\ **Post date:** [April 11, 2023, 3:02pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/14 "2023-04-11T15:02:20Z")
@Gitbix it looks like there was a bug with the way dask vs. numpy arrays were saved to disk - this should resolve that issue, and I opened an issue on the xradar side to reflect these issues ```python # Open the original file file = 'cfrad.20211211_120304.494_to_20211211_120801.176_KBSI_SUR.nc' ds = xr.open_dataset(file) # Make sure that sweep number is one of the variables in the dataset ds['sweep_number'] = ('sweep', ds.sweep.values) # Make sure the full dataset is loaded, which ensures values are passed correctly ds = ds.compute() # Write this new netcdf file to disk ds.to_netcdf(file) # Read the data back in using xradar tree = xd.io.open_cfradial1_datatree(file) # Plot the second sweep, using the closest azimuth tree['sweep_1'].sel(azimuth=242, method='nearest').sel(range=slice(40_000, 50_000))['corrected_reflectivity'].plot() ``` Which resulted in this plot ![Screenshot 2023-04-11 at 10.01.55 AM](https://global.discourse-cdn.com/free1/uploads/openradar/original/1X/c15e3d1b5d3296d78170f8b49d2611b8b668abb8.jpeg) ---
**Author:** ![Gitbix](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/gitbix/32/144_2.png) [@Gitbix](https://openradar.discourse.group/u/Gitbix)\ **Post date:** [April 11, 2023, 4:29pm UTC](https://openradar.discourse.group/t/extract-a-radar-column-along-a-line-of-azimuth/207/15 "2023-04-11T16:29:24Z")
Oh really. I would check the opened issue. Thank you sir