On Sun, Oct 7, 2012 at 8:55 PM, Camilo Mora <cmora@dal.ca> wrote:

> Thanks Robert,
>
> I am exploring an option suggested by Barry and would like to explore
> yours to. A question I have though is how to use "extract" to a raster.
> According to the instructions extract takes the data from a raster on the
> areas overlapping polygons, lines, points and extents. But not info on
> other rasters. Is there a trick to extract to another raster?



I thought you mentioned the trick yourself, as you "converted my habitat
raster to points and used the "extract" function".
After the extraction you could create a new raster with the extracted
values.



>
>
> Thanks,
>
> Camilo
>
>
> Camilo Mora, Ph.D.
> Department of Geography, University of Hawaii
> Currently available in Colombia
> Phone:   Country code: 57
>          Provider code: 313
>          Phone 776 2282
>          From the USA or Canada you have to dial 011 57 313 776 2282
> http://www.soc.hawaii.edu/**mora/ <http://www.soc.hawaii.edu/mora/>
>
>
>
> Quoting "Robert J. Hijmans" <r.hijmans@gmail.com>:
>
>  On Sun, Oct 7, 2012 at 10:58 AM, Camilo Mora <cmora@dal.ca> wrote:
>>
>>  Thanks Barry,
>>>
>>> I did try resample. Unfortunately, it is taking about 15 minutes and
>>> after
>>> that it says that it failed returning the message "Reached total
>>> allocation
>>> of 5813Mb: see help(memory.size)".
>>>
>>>
>>>  I have made some changes in resample to hopefully avoid this in the
>> future.
>> You can probably also avoid this lowering the default values for chunksize
>> and maxmemory (see ?setOptions)
>>
>>
>>  I converted my habitat raster to points (about 500,000) and use the
>>> "extract" fucntion. it does the extraction in about two minutes, which
>>> makes me realize that the resample function is taking to long because of
>>> the interpolation method.
>>>
>>>
>>
>> You could use
>>
>> extract(   , method='bilinear')
>>
>> assuming that you two rasters have more or less the same resolution (or at
>> least that the resolution of the raster where you extract values from is
>> not much higher than that of the other raster)
>>
>>
>>
>>
>>> Do you know if there is an analogous function to resample that considers
>>> just the overlap of cells to assing values?.
>>>
>>> Thanks,
>>>
>>>
>>> Camilo
>>> http://www.soc.hawaii.edu/****mora/ <http://www.soc.hawaii.edu/**mora/><
>>> http://www.soc.hawaii.edu/**mora/ <http://www.soc.hawaii.edu/mora/>>
>>>
>>>
>>>
>>>
>>>
>>> Quoting Barry Rowlingson <b.rowlingson@lancaster.ac.uk>****:
>>>
>>>  On Sun, Oct 7, 2012 at 7:56 AM, Camilo Mora <cmora@dal.ca> wrote:
>>>
>>>>
>>>>  Hi:
>>>>> I wonder if anyone knows a function to extract values from one raster
>>>>> to another raster when the rasters differ in resolution and extent. In
>>>>> other words extracting values just in overlapping cells.
>>>>>
>>>>> This is my specific problem: I have two rasters (one is for
>>>>> temperature worldwide and the other is for the presence of reefs also
>>>>> worldwide (the presence of reefs have values of 1 and all other cells
>>>>> as NA)). (the rasters differ in resolution and extent). I just need to
>>>>> put the values of the raster of temperature to each cell in the raster
>>>>> of reefs. Will you know a function that may do this?
>>>>>
>>>>>
>>>>  You want to start off looking at the 'resample' function in the
>>>> raster package. Read the note at the start of that about other
>>>> possibilities. Since your cells don't line up, there's various ways of
>>>> deciding what the value for a target cell is, including just sampling
>>>> the centre points, or interpolating overlapping cells in various ways.
>>>>
>>>> Barry
>>>>
>>>>
>>>>
>>>>  ______________________________****_________________
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>>
>
>
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