[R-sig-Geo] raster - unrotate?

[Michael Sumner]

On Thu, 22 Jun 2017 at 21:28 Ben Tupper <btupper at bigelow.org> wrote:

> Hi,
>
> Wow!  A treasure from the past!
>
> Hmmm.   I see what you mean; it might be best to snip-clip-and-smush from
> the native presentation.  We are testing out the performance of the dineof
> function in the sinkr package (
> https://github.com/marchtaylor/sinkr/blob/master/R/dineof.R) to
> interpolate patchy chlorophyl data.
>
> Thanks for the tip!
>
>

For what it's worth, I'm happy to help, there's no one size fits all here.
The dateline is one of those "easy problems" that does not have a general
fix and will bite in many different contexts. :)

The best distillation of my tricks is in this project, but it does depend
on your workflow and the actual data in use.

https://github.com/hypertidy/tabularaster

If you have performance issues raster's cell abstraction  will help, but
they are a bit old-school when it comes to multi-part geometries. (It's
identical to standard database indexing concepts as are all "spatial"
optimization tricks)

(I see a desperate need for a general API for this kind of problem so that
we can build tools from a general framework, which I'm working on - that's
some kind of excuse for why this and related projects are quite raw and
unfinished.)

Cheers, Mike.

Cheers,
> Ben
>
> On Jun 22, 2017, at 4:46 AM, Michael Sumner <mdsumner at gmail.com> wrote:
>
>
> It used to do the inverse, and I preserved a copy of the old behaviour
> here:
>
>
> https://github.com/AustralianAntarcticDivision/raadtools/blob/master/R/utils.R#L9
>
> You're probably best to learn from how it approaches it rather than just
> use it, since it's not a general capability, just works for those very
> specific cases.
>
> I just tested it and it still seems to work fine, I used
>
>
> oceandata.sci.gsfc.nasa.gov/MODISA/Mapped/Monthly/9km/chlor/A20021822002212.L3m_MO_CHL_chlor_a_9km.nc
>
>
> obtainable with
>
>
> https://oceandata.sci.gsfc.nasa.gov/cgi/getfile/A20021822002212.L3m_MO_CHL_chlor_a_9km.nc
>
>
> If you're extracting points you might as well just convert them into the
> "Atlantic" range, but it's painful to get that right for polygons or lines
> (and very hard to generalize once you get it working anyway).
>
> For simple regions like the one you show I'd probably split it into two
> extents() and use those - but depends on your workflow, all these options
> are useful here and there.
>
> Cheers, Mike.
>
>
> On Thu, 22 Jun 2017 at 18:30 Ben Tupper <btupper at bigelow.org> wrote:
>
>> Hello,
>>
>> We have rasters that span [-180, 180] from NASA's Ocean Color (
>> https://oceancolor.gsfc.nasa.gov/)  datasets.  We are trying to extract
>> a region that spans 100E to 90W, that is 100 to -90.  The region 'wraps'
>> across the edges as shown by the plot at the address below.
>>
>> https://dl.dropboxusercontent.com/u/8433654/sst.png
>>
>>
>> library(raster)
>> uri <- '
>> https://oceandata.sci.gsfc.nasa.gov:443/opendap/MODISA/L3SMI/2016/001/A20160012016032.L3m_R32_SST_sst_9km.nc
>> <https://oceandata.sci.gsfc.nasa.gov/opendap/MODISA/L3SMI/2016/001/A20160012016032.L3m_R32_SST_sst_9km.nc>
>> '
>> R <- raster::raster(uri, varname = 'sst')
>>
>> R
>> #class       : RasterLayer
>> #dimensions  : 180, 360, 64800  (nrow, ncol, ncell)
>> #resolution  : 1, 1  (x, y)
>> #extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
>> #coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
>> #data source : in memory
>> #names       : layer
>> #values      : 1.482572e-05, 0.9999928  (min, max)
>>
>> plot(R)
>> lines(c(180, 100, 100, 180), c(80,80,0,0))
>> lines(c(-180,-90,-90,-180), c(80,80,0,0))
>>
>> I see that there is the nice raster::rotate() function to rotate raster
>> coordinates from [0,360] to [-180,180]. That would make extracting the
>> region super easy if the inverse were available.  Is there an equivalent
>> way to implement the inverse or raster::rotate()?  I could dig into the
>> source of raster::rotate() to see how to code one up, but I hate like heck
>> to reinvent the wheel.
>>
>> Thanks!
>> Ben
>>
>>
>> Ben Tupper
>> Bigelow Laboratory for Ocean Sciences
>> 60 Bigelow Drive, P.O. Box 380
>> East Boothbay, Maine 04544
>> http://www.bigelow.org
>>
>> _______________________________________________
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>> R-sig-Geo at r-project.org
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
> --
> Dr. Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> 203 Channel Highway
> Kingston Tasmania 7050 Australia
>
>
> Ben Tupper
> Bigelow Laboratory for Ocean Sciences
> 60 Bigelow Drive, P.O. Box 380
> East Boothbay, Maine 04544
> http://www.bigelow.org
>
>
>
> --
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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