[R-sig-Geo] sp:gIntersection warning message about projection

[Monica Palaseanu-Lovejoy]

Hi Akos,

Thanks for your answer. I tried your suggestion, and for:

> proj4string(pln) <- proj4string(buff)
Warning messages:
1: In proj4string(buff) : CRS object has comment, which is lost in output
2: In proj4string(obj) : CRS object has comment, which is lost in output

> pln <- spTransform(pln, proj4string(buff))
Warning message:
In proj4string(buff) : CRS object has comment, which is lost in output

> proj4string(buff)
[1] "+proj=utm +zone=16 +datum=WGS84 +units=m +no_defs"
Warning message:
In proj4string(buff) : CRS object has comment, which is lost in output

I got these warnings, which again, i don't understand. I am trying to do an
R package that uses sp, and specifically gIntersection for my project and i
cannot leave it with those warnings.

But if after i have my two objects buff and pln and use these two
transforms you specified, where crs1 is my projection string "+proj=utm
+zone=16 +datum=WGS84
+units=m +no_defs" :

pln <- spTransform(x = pln, CRSobj=crs1)
>
> buff<- spTransform(x = buff, CRSobj=crs1)
>
> p1 <- gIntersection(buff, pln)

Then, i get no warnings from the gIntersection function. I will test
further, but maybe this is the solution, although i still don't understand
why i need to transform my object with a projection when it already has
that projection.

Thanks again for your suggestion, it really helps ;-)

Take care,
Monica

##################################################################

Message: 2
Date: Wed, 21 Oct 2020 16:53:29 +0200
From: =?UTF-8?Q?Bede-Fazekas_=c3=81kos?= <bfalevlist using gmail.com>
To: r-sig-geo using r-project.org
Subject: Re: [R-sig-Geo] sp:gIntersection warning message about
        projection
Message-ID: <33da0968-ec27-89b3-6dc1-46d892309b93 using gmail.com>
Content-Type: text/plain; charset="iso-8859-2"; Format="flowed"

Hello Monica,

The format of CRS definition changed a lot in the last years. I saw
similar errors thrown by package sf, and transforming or CRS
modification solved the problem. Does rgeos::gIntersection() work if you
run one of the following lines before intersection?:
proj4string(pln) <- proj4string(buff)
pln <- spTransform(pln, proj4string(buff))
pln <- spTransform(x = pln, CRSobj = "+proj=utm +zone=16 +datum=WGS84
+units=m +no_defs"); buff<- spTransform(x = buff, CRSobj = "+proj=utm
+zone=16 +datum=WGS84 +units=m +no_defs")

Have a nice week,
Ákos Bede-Fazekas
Hungarian Academy of Sciences

2020.10.21. 16:29 keltezéssel, Monica Palaseanu-Lovejoy írta:
>   Hi,
>
> I am using in my workflow gIntersection from sp package. Part of my
> relevant sessionInfo is:
> R version 4.0.3 (2020-10-10)
> Platform: x86_64-w64-mingw32/x64 (64-bit)
> Running under: Windows 10 x64 (build 17763)
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] CircStats_0.2-6 boot_1.3-25     MASS_7.3-53     stringr_1.4.0
> [5] rgeos_0.5-5     maptools_1.0-2  rgdal_1.5-18    raster_3.3-13
> [9] sp_1.4-4
>
>
> So i am using 2  SpatialLinesDataFrame that are results of previous
> computation. I am not sure i can give a viable examples, but maybe this
can
> be solved without. If not i will figure out how i can give you a workable
> example. Or if you know if there are in R already loaded 2 different line
> shapefiles with projection then i will see if i can replicate this
problem.
>
> But the main point is that my workflow was fine in R 4.0.0 and the older
sp
> version, and after i upgraded to the newest R and updated all packages i
am
> getting the projection warning.
>
> So, first file:
>
>   buff
> class       : SpatialLinesDataFrame
> features    : 1
> extent      : 560525.5, 561302.4, 4698908, 4701110  (xmin, xmax, ymin,
ymax)
> crs         : +proj=utm +zone=16 +datum=WGS84 +units=m +no_defs
> variables   : 2
> names       : ID, buff_dist
> value       :  2,       135
>
> second file:
>
> pln
> class       : SpatialLinesDataFrame
> features    : 1
> extent      : 560615.6, 560705.4, 4698905, 4699180  (xmin, xmax, ymin,
ymax)
> crs         : +proj=utm +zone=16 +datum=WGS84 +units=m +no_defs
> variables   : 2
> names       :                x,                y
> value       : 560615.564407584, 4698904.71208346
>
> Please observe that both files have identical projections.
>
> p1 <- gIntersection(buff, pln)
> Warning message:
> In RGEOSBinTopoFunc(spgeom1, spgeom2, byid, id, drop_lower_td,
> unaryUnion_if_byid_false,  :
>    spgeom1 and spgeom2 have different proj4 strings
>
> This warning is baffling since both files have same projection:
> crs(buff)
> CRS arguments:
>   +proj=utm +zone=16 +datum=WGS84 +units=m +no_defs
>
> crs(pln)
> CRS arguments:
>   +proj=utm +zone=16 +datum=WGS84 +units=m +no_defs
>
> Probably i am doing something wrong but for the life of me i cannot see it
> as yet.
>
> Thanks so much for any help, take care,
> Monica
>
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>
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