[ncl-talk] high resolution png image

Thu Oct 30 14:19:14 MDT 2014

Compared with high resolution PostScript files, high resolution PNG
images do seem to be much more cost effective in terms of file size
and quickness to load and manipulate by typical viewing tools like Mac
Preview.

Ideally you would want a PNG image that is close to the same
resolution as your data or higher. In order to get this with an NCL
"RasterFill" plot there are two things you need to adjust: the output
workstation resolution, controlled by "wkWidth" and "wkHeight", and
the resolution that the raster fill method uses when drawing, which is
most easily controlled by setting the resource "cnRasterCellSizeF" to
a suitable small number. Note that the workstation resources set a
resolution for the plot as a whole, including the annotations and any
white space that surrounds the plot, while the raster cell size only
relates to the area inside the viewport of the actual plot -- just
something to keep in mind.

For example, to visualize a 65,000,000 cell MPAS grid with maximum
possible detail, I set
wkWidth and wkHeight to 16384 (a power of 2 but not really necessary
-- it could have been 16000).
Then I set cnRasterCellSizeF to 1.0/16384.0  Nothing magical about
these numbers, and they don't account for the whole plot vs viewport
issue mathematically, but they do produce a very detailed image. The
output PNG file is about 40 MB -- too big to attach to this message
unfortunately.

We should probably have an example or two showing how to create
high-res graphics.
 -dave

On Thu, Oct 30, 2014 at 11:30 AM, Micah Sklut <micahs2005 at gmail.com> wrote:
> Okay, thanks for explaining how the raster fill works Kyle. That does help
> me understand this limitation. With respect to processing time between
> rasterFill and areaFill. It took about 1-2 minutes for rasterFill, compared
> to a ball park of 4 hours for areaFill. Quite a difference!
>
> On Thu, Oct 30, 2014 at 1:26 PM, Kyle Griffin <ksgriffin2 at wisc.edu> wrote:
>>
>> That's part of the definition of Raster fill - it will always create the
>> same number of boxes regardless of resolution of the data underneath,
>> typically based on an average of the data points within that set of grid
>> points. Although I'm not knowledgeable about the behind-the-scenes
>> computations, I know it's common for NCL to mark the whole average as
>> missing if any subset of that average is missing. I'm not sure if there's a
>> way to override this - a developer might need to chime in here - but that
>> would be your only hope if you want to keep your image production time down,
>> as the other fill modes will almost certainly be more intensive. You can
>> scan examples of Raster Fill code here (see link) and in the contour
>> resources page as well.
>>
>> https://www.ncl.ucar.edu/Applications/raster.shtml
>>
>> If you did AreaFill or CellFill, I don't think you see much difference in
>> the time to produce a vector file output versus a raster image output. But
>> yes, what you are seeing is a limitation of using the RasterFill setting.
>>
>>
>> Kyle
>>
>> ----------------------------------------
>> Kyle S. Griffin
>> Department of Atmospheric and Oceanic Sciences
>> University of Wisconsin - Madison
>> Room 1421
>> 1225 W Dayton St, Madison, WI 53706
>> Email: ksgriffin2 at wisc.edu
>>
>> On Thu, Oct 30, 2014 at 11:55 AM, Micah Sklut <micahs2005 at gmail.com>
>> wrote:
>>>
>>> No, I"m not masking data. Yes, I am using RasterFill, and the resulting
>>> image for the Mid Atlantic is great. But, when I expand to global, I lose
>>> the high detail, no matter how much I increase the png resolution. So, just
>>> wondering why I am losing detail with the global image, and if there is a
>>> way around it.
>>>
>>> On Thu, Oct 30, 2014 at 12:52 PM, Kyle Griffin <ksgriffin2 at wisc.edu>
>>> wrote:
>>>>
>>>> Hi Micah,
>>>>
>>>> This seems to me the type of result you would expect when using
>>>> RasterFill as a cnFillMode - the default should be cnAreaFill, which
>>>> increases plot time significantly, but might that be an issue?
>>>> Otherwise, I assume you're doing nothing else to mask the data, correct?
>>>> Sometimes masking data with a land mask can create similar blockiness,
>>>> although I am unaware (via inexperience) as to whether there is a resolution
>>>> dependence based on the plot size or native data resolution.
>>>>
>>>>
>>>> Kyle
>>>>
>>>> ----------------------------------------
>>>> Kyle S. Griffin
>>>> Department of Atmospheric and Oceanic Sciences
>>>> University of Wisconsin - Madison
>>>> Room 1421
>>>> 1225 W Dayton St, Madison, WI 53706
>>>> Email: ksgriffin2 at wisc.edu
>>>>
>>>> On Thu, Oct 30, 2014 at 11:37 AM, Micah Sklut <micahs2005 at gmail.com>
>>>> wrote:
>>>>>
>>>>> Hi Kyle,
>>>>>
>>>>> Thanks for the reply.
>>>>>
>>>>> The dataset is of 0.05 degree resolution, so that certainly isn't the
>>>>> problem. I have attached an image of the same data, but limiting the min/max
>>>>> lat/lon to the US Mid Atlantic. In this image you will see much more detail.
>>>>> This is the type of detail I was hoping to achieve for the entire globe. I
>>>>> figured if I increased the resolution of the global png, it would create the
>>>>> desired effect, but as you can see from the global image I attached, this
>>>>> wasn't the case.
>>>>>
>>>>> Looking forward to hearing your thoughts.
>>>>> Thank you,
>>>>>
>>>>> Micah
>>>>>
>>>>>
>>>>>
>>>>> On Thu, Oct 30, 2014 at 12:26 PM, Kyle Griffin <ksgriffin2 at wisc.edu>
>>>>> wrote:
>>>>>>
>>>>>> Micah,
>>>>>>
>>>>>> This looks more like a limitation of your dataset - SST data is not of
>>>>>> infinite resolution, and you're plotting far more pixels than would be data
>>>>>> points in even a 0.1˚ dataset! It looks like the internal pixels are the
>>>>>> same size as your coastlines, so I don't see an issue with NCL there. More
>>>>>> specifically, you are not actually plotting coastlines - they only plot if
>>>>>> you tell them to plot with a call to gsn_csm_map or another similar plotting
>>>>>> tool. If you're looking for high resolution coastlines, look at the RANGS
>>>>>> mapping capabilities in NCL. Beyond that, you can always plot shapefiles as
>>>>>> well.
>>>>>>
>>>>>> Yes, vector images are going to be extremely large and painful for
>>>>>> even a moderate resolution file over the full globe. When you say raster,
>>>>>> are you talking about it in the image sense (non-vector file) or in the
>>>>>> cnFillMode sense (RasterFill, AreaFill, etc.;
>>>>>> https://www.ncl.ucar.edu/Document/Graphics/Resources/cn.shtml#cnFillMode)?
>>>>>> Raster fill mode will make the data more blocky and reduce interpolation
>>>>>> between points, but the trade-off is a much faster plotting of the image and
>>>>>> works well for high-resolution datasets being plotted at relatively low
>>>>>> resolution/wide zoom.
>>>>>>
>>>>>>
>>>>>> Kyle
>>>>>>
>>>>>> ----------------------------------------
>>>>>> Kyle S. Griffin
>>>>>> Department of Atmospheric and Oceanic Sciences
>>>>>> University of Wisconsin - Madison
>>>>>> Room 1421
>>>>>> 1225 W Dayton St, Madison, WI 53706
>>>>>> Email: ksgriffin2 at wisc.edu
>>>>>>
>>>>>> On Thu, Oct 30, 2014 at 9:58 AM, Micah Sklut <micahs2005 at gmail.com>
>>>>>> wrote:
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> This is a follow up to my previous posts, in reference to searching
>>>>>>> for high resolution images that could be used as zooming/navigating
>>>>>>> (specific interest is with image tile layers).
>>>>>>>
>>>>>>> I figured if I created a png file with a high resolution, it would be
>>>>>>> able to capture the high detail, like with coastlines and so forth.
>>>>>>> I've attached an image with very high resolution (16384x16384), but
>>>>>>> as you can see, if you zoom the global image into the coastlines they are
>>>>>>> extremely blocky.
>>>>>>>
>>>>>>> Is is possible to capture high resolution features, such as
>>>>>>> coastlines in a global raster image with NCL?
>>>>>>>
>>>>>>> FYI, I tried the vector image route, but the file size was gigantic,
>>>>>>> so that didn't seem like a proper route.
>>>>>>>
>>>>>>> Thank you,
>>>>>>>
>>>>>>> --
>>>>>>> Micah Sklut
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> ncl-talk mailing list
>>>>>>> List instructions, subscriber options, unsubscribe:
>>>>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Micah Sklut
>>>>>
>>>>
>>>
>>>
>>>
>>> --
>>> Micah Sklut
>>>
>>
>
>
>
> --
> Micah Sklut
>
>
> _______________________________________________
> ncl-talk mailing list
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>