[R-sig-Geo] sp::spDists*

[Edzer Pebesma]

A new version of gstat, fixing the same bug, is now also on CRAN.

On 09/01/17 11:39, Roger Bivand wrote:
> New versions of spdep and spgwr fixing the same bug are now on CRAN.
> 
> Roger
> 
> On Thu, 8 Dec 2016, Edzer Pebesma wrote:
> 
>> While building support for geosphere distance functions in sf and
>> comparing results from geosphere::distMeeuws with those of sp::spDists,
>> I found a typo in the C code underlying the great circle distance
>> computation functions in sp (sp::spDists, sp::spDistsN1) [*]:
>>
>> https://github.com/edzer/sp/commit/d8374ff7efc6735cba9a054748c602bed0672f23
>>
>>
>> Before:
>>> library(sf)
>> Linking to GEOS 3.5.0, GDAL 2.1.0, proj.4 4.9.2
>>> library(sp)
>>> library(units)
>>>
>>> x = st_sfc(
>> + st_point(c(0,0)),
>> + st_point(c(1,0)),
>> + st_point(c(2,0)),
>> + st_point(c(3,0)),
>> + crs = 4326
>> + )
>>>
>>> y = st_sfc(
>> + st_point(c(0,10)),
>> + st_point(c(1,0)),
>> + st_point(c(2,0)),
>> + st_point(c(3,0)),
>> + st_point(c(4,0)),
>> + crs = 4326
>> + )
>>>
>>> st_distance(x, y)
>> Units: m
>>        [,1]     [,2]     [,3]     [,4]     [,5]
>> [1,] 1105855 111319.5 222639.0 333958.5 445278.0
>> [2,] 1111387      0.0 111319.5 222639.0 333958.5
>> [3,] 1127822 111319.5      0.0 111319.5 222639.0
>> [4,] 1154693 222639.0 111319.5      0.0 111319.5
>>>
>>> d.sf = st_distance(x, y, geosphere::distMeeus)
>>> d.sp = spDists(as(x, "Spatial"), as(y, "Spatial"))
>>> units(d.sp) = make_unit("km")
>>> d.sf - d.sp
>> Units: m
>>         [,1]         [,2]         [,3]         [,4] [,5]
>> [1,] 1851.990 0.000000e+00 0.000000e+00 0.000000e+00    0
>> [2,] 1842.938 0.000000e+00 0.000000e+00 2.910383e-11    0
>> [3,] 1816.564 0.000000e+00 0.000000e+00 1.455192e-11    0
>> [4,] 1775.032 2.910383e-11 1.455192e-11 0.000000e+00    0
>>>
>>
>>
>>
>> After:
>>
>>> library(sf)
>> Linking to GEOS 3.5.0, GDAL 2.1.0, proj.4 4.9.2
>>> library(sp)
>>> library(units)
>>>
>>> x = st_sfc(
>> + st_point(c(0,0)),
>> + st_point(c(1,0)),
>> + st_point(c(2,0)),
>> + st_point(c(3,0)),
>> + crs = 4326
>> + )
>>>
>>> y = st_sfc(
>> + st_point(c(0,10)),
>> + st_point(c(1,0)),
>> + st_point(c(2,0)),
>> + st_point(c(3,0)),
>> + st_point(c(4,0)),
>> + crs = 4326
>> + )
>>>
>>> st_distance(x, y)
>> Units: m
>>        [,1]     [,2]     [,3]     [,4]     [,5]
>> [1,] 1105855 111319.5 222639.0 333958.5 445278.0
>> [2,] 1111387      0.0 111319.5 222639.0 333958.5
>> [3,] 1127822 111319.5      0.0 111319.5 222639.0
>> [4,] 1154693 222639.0 111319.5      0.0 111319.5
>>>
>>> d.sf = st_distance(x, y, geosphere::distMeeus)
>>> d.sp = spDists(as(x, "Spatial"), as(y, "Spatial"))
>>> units(d.sp) = make_unit("km")
>>> d.sf - d.sp
>> Units: m
>>              [,1]         [,2]         [,3]         [,4] [,5]
>> [1,] -2.328306e-10 0.000000e+00 0.000000e+00 0.000000e+00    0
>> [2,]  2.328306e-10 0.000000e+00 0.000000e+00 2.910383e-11    0
>> [3,]  0.000000e+00 0.000000e+00 0.000000e+00 1.455192e-11    0
>> [4,]  0.000000e+00 2.910383e-11 1.455192e-11 0.000000e+00    0
>>>
>>
>> [*] assuming the source code of
>> http://www.abecedarical.com/javascript/script_greatcircle.html is
>> correct; I don't have access to the Meeuws book mentioned there under
>> (1).
>>
>> The same C function is used by gstat; I corrected that as well.
>>
> 

-- 
Edzer Pebesma
Institute for Geoinformatics  (ifgi),  University of Münster
Heisenbergstraße 2, 48149 Münster, Germany; +49 251 83 33081
Journal of Statistical Software:   http://www.jstatsoft.org/
Computers & Geosciences:   http://elsevier.com/locate/cageo/

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