convert point and map coordinates UTM to WSG

spDistsN1(coordinates(SP.wgs),coordinates(SP.utm.wgs[1,]),longlat=TRUE)[1]*1000

spDistsN1(coordinates(SP.wgs),coordinates(SP.utm.wgs[2,]),longlat=TRUE)[2]*1000

spDistsN1(coordinates(SP.wgs),coordinates(SP.utm.wgs[3,]),longlat=TRUE)[3]*1000

spDistsN1(coordinates(SP.wgs),coordinates(SP.utm.wgs[4,]),longlat=TRUE)[4]*1000

On Wed, 1 Apr 2009, Marc Mar? Dell'Olmo wrote:

Dear all,

I have tried to transform coordinates from UTM Zone-31 ED-50 Spain Portugal
(EUR-D code in this web
http://earth-info.nga.mil/GandG/coordsys/onlinedatum/CountryEuropeTable.html#
EURD) to coordinates WSG84 ( google maps coordinates) with the
"ptransform" of the proj4 library and I can not do it right (first syntax).
I have tried also using the "spTransform" of the rgdal ?library (second
syntax) and I have not been successful.

I attach the syntax used, I got 4 points with coordinates ED ESP-50 ( "utm"
in the syntax) and their respective coordinates WSG84 (wgs.gold "in the
syntax). Can anyone tell me where is the error?

So far several. One is reversing x and y values, another saying "latlong" when you mean "longlat", a third is the units of your input UTM (I think mm, not m), here, I'm going from longlat to UTM:

library(rgdal)

y.wgs <- c(41.4036923115558, 41.38010926480547, 41.41148169051035,
?41.409534433320914)
x.wgs <- c(2.145810127258301, 2.1807003021240234, 2.2183799743652344,
?2.1170568466186523)
SP <- SpatialPoints(cbind(x.wgs, y.wgs),
?proj4string=CRS("+proj=longlat +datum=WGS84"))
spTransform(SP,
?CRS("+proj=utm ?+ellps=intl +zone=31 +towgs84=-84,-107,-120,0,0,0,0,0"))

The remaining differences are from the inadequacy of the +towgs84 string; Grids & Datums (http://www.asprs.org/resources/grids/) - like your source - gives +/- ranges for the transformation parameters, so you'll need to fish unless you can get a better authority (and there are few better than Grids & Datums).

Hope this helps,

Roger

Thank you very much,

Marc

#First sintax
library(proj4)
x.utm <- c(428727134,431587743,434639340,426268557)
y.utm <- c(4584118048,4581465377,4584855001,4584607449)
x.wgs <-

c(41.4036923115558,41.38010926480547,41.41148169051035,41.409534433320914)

y.wgs <-

c(2.145810127258301,2.1807003021240234,2.2183799743652344,2.1170568466186523)

utm <- cbind(x.utm, y.utm)
wgs.new <- ptransform(utm, "+proj=utm ?+ellps=intl +zone=31

+towgs84=-84,-107,-120,0,0,0,0,0 +no_defs",
+ ? ? ? ? ? ? ? ? ?"+proj=latlong ?+datum=WGS84")

wgs.new

? ? ? ? [,1] ? ? [,2] ? ? [,3]
[1,] -2.236353 1.570775 39.63333
[2,] -2.236353 1.570775 39.63333
[3,] -2.236353 1.570775 39.63333
[4,] -2.236353 1.570775 39.63333

(wgs.gold <- cbind(x.wgs, y.wgs))

? ? ? x.wgs ? ?y.wgs
[1,] 41.40369 2.145810
[2,] 41.38011 2.180700
[3,] 41.41148 2.218380
[4,] 41.40953 2.117057

#Second sintax
library(rgdal)
(data.utm <- data.frame(x.utm,y.utm,x.wgs,y.wgs))

? ? x.utm ? ? ?y.utm ? ?x.wgs ? ?y.wgs
1 428727134 4584118048 41.40369 2.145810
2 431587743 4581465377 41.38011 2.180700
3 434639340 4584855001 41.41148 2.218380
4 426268557 4584607449 41.40953 2.117057

coordinates(data.utm) <- c("x.utm", "y.utm")
proj4string(data.utm) <- CRS("+proj=utm ?+ellps=intl +zone=31

+towgs84=-84,-107,-120,0,0,0,0,0 +no_defs")

(wgs.new2 <- spTransform(data.utm, CRS("+proj=latlong +datum=WGS84")))

? ? ? ? coordinates ? ?x.wgs ? ?y.wgs
1 (-128.134, 89.9988) 41.40369 2.145810
2 (-128.134, 89.9988) 41.38011 2.180700
3 (-128.134, 89.9988) 41.41148 2.218380
4 (-128.134, 89.9988) 41.40953 2.117057



2009/3/23 Paul Hiemstra <p.hiemstra at geo.uu.nl>

Hi,

To transform coordinates you can use the spTransform function from the
rgdal pacakge. It uses proj4 to do the transformations. Proj uses a string
to describe a certain projection, the so called proj4string. If you can
determine the proj4string for both your projections you can transform
between them. The first string (WGS84) looks like this:

"+proj=longlat +datum=WGS84"

The second (UTM) something like:

"+proj=utm +zone=yourzone +datum=yourdatum"

See the documentation of spTransform for more information on how to use the
function.

cheers and hth,
Paul


Marc Mar? Dell'Olmo wrote:

Dear R-users,

Can anyone tell me how to convert point coordinates from WSG84 (google
maps coordinates) format to UTM HUSO-31 ED-50. And if I have a map
(shp format) with UTM HUSO-31 ED-50 coordinates, how can I convert to
WSG84 (google maps coordinates) coordinates. Should I install some
external software?

Can anyone tell me the instructions?

Thank you,

Marc

--
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Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
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Phone: ?+3130 274 3113 Mon-Tue
Phone: ?+3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul <http://intamap.geo.uu.nl/%7Epaul>

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