[ncl-talk] Fill entire plot area

Mary Haley haley at ucar.edu
Thu Jul 31 10:01:17 MDT 2014


You can't fill a square area with a non-square map, and preserve the aspect
ratio at the same time. In your last email, you stated that you needed to
preserve the aspect ratio.

Since NCL wants to draw to a square, it's going to fill as much of the
square as possible (if you set the vp* resources, which you did), but it
won't skew the aspect ratio.

If you give a pixel size of 2000 x 2000 (width x height) and your image is
twice as long as it is high, then what happens is your image will be 2000 x
1000, with approximately 500 pixels of white space above and below the
image. There are ways to force the image to have all the white space at the
bottom or the top, if that's what you need.

Can you be more specific about what you are hoping to get, that's not
inline with what you are getting out of NCL?


On Wed, Jul 30, 2014 at 11:04 PM, Rabah Hachelaf <hachelaf at sca.uqam.ca>

> Hi Mary,
> Thanks for this working suggestion, but when trimming the image the pixel
> size change, i must keep the same pixel size in each image side because
> those images will feed a viewing software like.
> Is there another trick to fill the plot area and keep same pixel size.
> Thanks again
> Rabah
> 2014-07-30 10:39 GMT-04:00 Mary Haley <haley at ucar.edu>:
> Hi Rabah,
>> One of NCL's quirks is that it always wants to draw things to a square,
>> so even when you have a non-square plot, like with a lat/lon projection
>> that may be wider than it is high, there is still an invisible square area
>> that NCL is plotting to. You will see this especially when you are plotting
>> graphics to an X11 window or a PNG image.
>> There's not much you can do about the X11 window being square, but you
>> can trim the PNG image.
>>  The way I trim the PNG image is to use a tool called "convert" which is
>> part of the free ImageMagick package.   "convert" is a handy tool that
>> allows you to convert from one format to another (like PS to PNG, GIF to
>> JPEG, and PNG to PNG), while at the same time trimming additional white
>> space, resizing the image, cropping an image, etc.
>> Once you have "convert" you can use it directly in your NCL script via a
>> system call, to trim the white space.
>> So, for example, with the script you included, I would do something like
>> this when calling "gsn_open_wks":
>>   wks_type          = "png"
>>   wks_type at wkWidth  = pixel
>>   wks_type at wkHeight = pixel
>>   wks_type at wkBackgroundOpacityF = 0.0
>>   wks_filename = "wx_map_" + "zoom" + zoom + "_" + "DOM" + \
>>                   sprinti("%0.1i",idom+1) +  "_" + \
>>                   lev_str(ilev) + "_" + sprinti("%0.2i", i)
>>   wks = gsn_open_wks(wks_type,wks_filename)
>> Then, after you call "draw" and "frame" on the workstation, you need to
>> "delete" the workstation, which merely ensures that the PNG image is
>> properly closed. This allows you to then call "convert" to trim the image:
>>   draw(wks)      ;; Now draw map with text strings and               frame(wks)
>>     ; advance the frame
>>   delete(wks)    ; Close the PNG image
>> ;---Trim the PNG image
>>   png_filename = wks_filename + ".png"
>>   cmd = "convert -trim " + png_filename + " " + png_filename
>>   system(cmd)
>> You can get the ImageMagick suite of tools from:
>> http://www.imagemagick.org
>> --Mary
>> On Tue, Jul 29, 2014 at 7:59 AM, Rabah Hachelaf <hachelaf at sca.uqam.ca>
>> wrote:
>>> Hi all,
>>> I am using the script attached to plot sub-domains from GFS data.
>>>  When i plot the whole domain or a 1/4 domain area the plot fit
>>> correctly with the entire plot area.
>>> But when i want plot 1/16 the plotted map does't fit and there is a
>>> white bands appear some time on top and bottom and some times on right and
>>> left.(like attached images).
>>> I tried mpShapeMode  = "FreeAspect", this make my maps fit with the
>>> entire plot area but this not preserve the map projection aspect ratio
>>> Thank you for any suggestions.
>>> --
>>> ------------------------------
>>> Cordialement,
>>> Best regards,
>>> Rabah Hachelaf
>>> _______________________________________________
>>> ncl-talk mailing list
>>> List instructions, subscriber options, unsubscribe:
>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
> --
> ------------------------------
> Cordialement,
> Best regards,
> Rabah Hachelaf
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