[ncl-talk] Problem aligning data with map
Mary Haley
haley at ucar.edu
Fri Mar 30 13:02:07 MDT 2018
Hi Chris,
Wow, I did not know that tfDoNDCOverlay was no longer a boolean! I've been
using it that way for years. It turns out this was changed sometime around
year 2000. Probably a Y2K thing. :-)
I will update the documentation to be more clear on the values, but here's
an explanation:
The values for tfDoNDCOverlay can be:
NhlDATATRANSFORM = 0
NhlNDCVIEWPORT = 1
NhlNDCDATAEXTENT = 2
Since you can use 0 and 1 integer values to represent False and True
respectively, it still works to set tfDoNDCOverlay to True, because that
translates to the NhlNDCVIEWPORT setting.
To answer your question, then, the following three settings of
tfDoNDCOverlay are equivalent to each other:
res at tfDoNDCOverlay = 0
res at tfDoNDCOverlay = False
res at tfDoNDCOverlay = "DataTransform"
res at tfDoNDCOverlay = 1
res at tfDoNDCOverlay = True
res at tfDoNDCOverlay = "NDCViewport"
res at tfDoNDCOverlay = 2
res at tfDoNDCOverlay = "NDCDataExtent"
[There's no "Nhl" in the string.]
Note that the string settings are case insensitive, so "DataTransform" can
be specified with "datatransform" which is the same as "DaTaTranSfORM", etc.
I have no idea how the third "NDCDataExtent" option is supposed to work. I
see a description about it being used when the mpShapeMode is set to
"FixedAspectNoFitBB", but I have no idea what that is either.
Maybe somebody on ncl-talk is more enlightened than me on this? I would
love to hear if anybody is using this third option.
--Mary
On Thu, Mar 29, 2018 at 2:24 PM, Herbster, Christopher G. <herbstec at erau.edu
> wrote:
> Thanks Mary!
>
>
>
> First, I am sorry for the slow response. Yesterday was one of those days
> ….
>
>
>
> Right after I sent my original email I realized that the difference in the
> three plots (and software used) was that we had done the subset for the NCL
> plots.
>
>
>
> Some of this code was written last year by a student with “guidance” from
> me. It was probably more likely pointing at documentation at the NCL web
> site than getting real guidance like a new programmer should have. I
> should have been more careful in thinking it all through, but I don’t get
> to code in NCL regularly enough to retain all the details.
>
>
>
> One last question (for now). The documentation for tfDoNDCOverlay says it
> is a Boolean (i.e. just two possible choices, but there are three options
> under the section in the documentation. I know part of my confusion is
> related to not really understanding the language, but how do I invoke the
> option NDCDataExtent?
>
> https://www.ncl.ucar.edu/Document/Graphics/Resources/tf.shtml
>
>
>
> Thanks again for the quick help!
>
>
>
> Chris H.
>
> --
>
>
>
> Dr. Christopher G. Herbster
>
> Associate Professor
>
> Director of Science and Technology
>
> for the ERAU Weather Center
>
> Applied Aviation Sciences
>
> Embry-Riddle Aeronautical Univ.
>
> 600 S. Clyde Morris Blvd.
> <https://maps.google.com/?q=600+S.+Clyde+Morris+Blvd.+%0D%0A+Daytona+Beach,+FL+32114&entry=gmail&source=g>
>
> Daytona Beach, FL 32114
> <https://maps.google.com/?q=600+S.+Clyde+Morris+Blvd.+%0D%0A+Daytona+Beach,+FL+32114&entry=gmail&source=g>
> -3900
>
> 386.226.6444 <(386)%20226-6444> Office
>
> 386.226.6446 <(386)%20226-6446> Weather Center
>
> http://wx.erau.edu/
>
>
>
> Schedule at: http://wx.erau.edu/faculty/herbster/Schedules/
>
>
>
> *From:* Mary Haley <haley at ucar.edu>
> *Sent:* Tuesday, March 27, 2018 6:58 PM
> *To:* Herbster, Christopher G. <herbstec at erau.edu>
> *Cc:* ncl-talk at ucar.edu
> *Subject:* Re: [ncl-talk] Problem aligning data with map
>
>
>
> Hi Chris,
>
>
>
> You were almost there.
>
>
>
> The issue is that you are subsetting your data by selecting a lat/lon area
> of interest, but then trying to plot this data using the projection defined
> for the original data. When you set the "tfDoNDCOverlay" resource to True,
> this signals to NCL that you are plotting data in its "native" projection,
> and hence you need to set the map parameters exactly right for the data you
> are plotting.
>
>
>
> If you are plotting the original data (see narr_plot.ncl), then you can
> use the map projection parameters on the file to plot the data. This script
> shows how to plot the data on both a cylindrical equidistant projection
> using the 2D lat/lon arrays read off the file, and in the native projection
> using map projection information attached to the lat/lon arrays. I've
> attached the PNGs from this script.
>
>
>
> If you want to zoom in on the data, then unless you know the exact
> projection parameters for the zoomed data, you will have to subset the 2D
> lat/lon arrays in the same fashion as the data, and use these for
> plotting. See the attached narr_plot_zoom.ncl and image.
>
>
>
> Finally, I took your original script and applied the same concepts I used
> in narr_plot_zoom.ncl. Instead of using tfDoOverlay, it uses the subsetted
> lat/lon arrays to get the overlay correct:
>
>
>
> res at sfXArray = lon2d_small
>
> res at sfYArray = lat2d_small
>
>
>
> Note that in narr_plot_zoom.ncl, I didn't use sfXArray / sfYArray.
> Instead, I used:
>
>
>
> var_subset at lat2d = lat_subset
>
> var_subset at lon2d = lon_subset
>
>
>
> These are essentially the same thing. I was just lazy and didn't want to
> have to attach the special "lat2d" and "lon2d" attributes to every variable
> being plotted.
>
>
>
> For more descriptive information on all this, you may want to visit our
> "plotting data on a map" page:
>
>
>
> http://www.ncl.ucar.edu/Applications/plot_data_on_map.shtml
>
>
>
> Let me know if you have any questions about what I did.
>
>
>
> --Mary
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> On Tue, Mar 27, 2018 at 3:02 PM, Herbster, Christopher G. <
> herbstec at erau.edu> wrote:
>
> Hi folks,
>
>
>
> Here is a sequence of events that we are using to download some NARR data
> from NOMADS at NCDC:
>
> We use the get-httpsubset.pl script from
>
> https://nomads.ncdc.noaa.gov/guide/index.php?name=advanced#adv-httpsubset
> and the Perl scripts from
>
> http://www.cpc.ncep.noaa.gov/products/wesley/fast_downloading_grib.html
> to grab a handful of parameters from the NARR dataset.
>
>
>
> This gives us GRIB files like:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-a_
> 221_20101201_1200_000.sub.grb
>
>
>
> I then used: ncl_convert2nc narr-a_221_20101201_1200_000.sub.grb -nc4c -l
>
> To make
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-a_
> 221_20101201_1200_000.sub.nc4
>
>
>
> I did this for 30 years of data ending 12-31-2010.
>
>
>
> We then used an NCL script to do some calculations on a month of data, and
> write the results into a new file.
>
> Here is the script:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/read_
> narr_ncar-help.ncl
>
> My apologies to those of you who actually know how to code in NCL. I am
> strictly an amateur at this.
>
>
>
> Here is the file we created:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/D-Value
> _Monthly_Stats.2010.12.averages.1200.nc
>
>
>
> Our problem seems to be aligning the data to the map background, as I can
> show with the following images:
>
>
>
> The grey area in this image is supposed to be where the terrain is higher
> than the calculated value:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-paper.000001.png
>
>
>
> The data mask area is too far to the west, even extending out over the
> ocean.
>
>
>
> When we plot it in the Unidata IDV we get what we expect:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/IDV_4K_Mask_D-Val.png
>
>
>
> Then we decided to try plotting it in Matlab as another test. We got:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/Matlab_
> Plot_NARR_Mask.jpg
>
>
>
>
>
> While I suspect that I am not doing something properly with the mapping of
> the data, I am also wondering about the results of making the NetCDF file
> from the ncl_convert command.
>
>
>
> First, is the compression lossy? I realized that the default compression
> is zero, so this step did not do much for disk space! (Actually made
> bigger files, but never mind.)
>
>
>
> When I load the original GRIB file into the IDV it displays the region
> properly without any problem. When I try to load the original NetCDF file,
> the IDV does not seem to know the geographic region of the data.
>
>
>
> This can be seen in the following images:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/load-both-idv.png
> shows the Mean Sea Level Pressure data from both files. They appear to
> match. However, when I added the second panel (NetCDF file), the IDV did
> not display the data properly, and did so only after I selected a
> predefined CONUS projection (as shown).
>
>
>
> When I open the NetCDF file and plotted MSLP in a window by itself, I got
> this:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/load-netcdf-idv.png
>
>
>
> I had to zoom way out to display this data. It knows where to put the
> data, but the IDV thinks the data should be in the white box area, I
> think. (I’m not really sure about this interpretation.)
>
>
>
> The questions I have are:
>
> 1) Why does this happen?
>
> 2) Is this related to my data masking and mapping problem, or are
> they separate issues?
>
>
>
> Thanks in advance for any help on any of these problems/questions.
>
>
>
> Cheers,
>
>
>
> Chris
>
>
>
> PS If you want to test our script, there is a month of data in this tar
> file:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/sample-narr.tgz
>
> --
>
>
>
> Dr. Christopher G. Herbster
>
> Associate Professor
>
> Director of Science and Technology
>
> for the ERAU Weather Center
>
> Applied Aviation Sciences
>
> Embry-Riddle Aeronautical Univ.
>
> 600 S. Clyde Morris Blvd.
> <https://maps.google.com/?q=600+S.+Clyde+Morris+Blvd.+%0D%0A+Daytona+Beach,+FL+32114&entry=gmail&source=g>
>
> Daytona Beach, FL 32114
> <https://maps.google.com/?q=600+S.+Clyde+Morris+Blvd.+%0D%0A+Daytona+Beach,+FL+32114&entry=gmail&source=g>
> -3900
>
> 386.226.6444 <(386)%20226-6444> Office
>
> 386.226.6446 <(386)%20226-6446> Weather Center
>
> http://wx.erau.edu/
>
>
>
> Schedule at: http://wx.erau.edu/faculty/herbster/Schedules/
>
>
>
>
> _______________________________________________
> ncl-talk mailing list
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