Hi Mehdi,
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
I don't mean to rude, but you seem to lack basic knowledge regarding the
use of spatial data in R. Starting to use R is hard, but please ask your
supervisor to help you or try and read more information on the internet.
Some hints:
The Spatial taskview:
http://cran.r-project.org/web/views/Spatial.html
The R tips wiki:
http://wiki.r-project.org/rwiki/doku.php?id=tips:spatial-data
Or read the sp-documentation:
?sp
vignette("sp")
In addition, there is a mailing list specifically for geographic data
and analysis in R, r-sig-geo. This is a much better place for your type
of questions.
I also have some comments inline below.
cheers and good luck with your R adventures!
Paul
Mehdi Khan wrote:
I imported the attached tiff file and converted the coordinate system to
long lat and graphed it:
californiatiff<- readGDAL("california1.tif")
proj4string(californiatiff)
What is the outcome of this command?
rasterprojection <- spTransform(californiatiff, CRS("+proj=longlat")
It seems that you reproject a grid here. Remember that when reprojecting
a grid, the grid structure is lost. The squares in the grid in the new
projection aren't squares anymore. So the output of spTransform is no
longer a grid (SpatialGrid or SpatialPixels) but a point dataset
(SpatialPoints).
however, when using the plot command for rasterprojection,
The sp-objects are plotted not using the plot command, but using the
spplot command. If you are using this, this is not obvious from your e-mail.
I get a blob. I
can see the outline of the state of california and nevada, but rather than
being able to see the geographic features, it is just a monocolor blob.
My
suspicion is that since it is a list of coordinates and another column that
contains attributes, I need to turn it into a polygon. I've tried the
following codes but none work:
rasterprojection2<-SpatialPolygons(rasterprojection)
You are trying to convert a grid to a polygon, this is not possible.
Error in is.vector(X) :
trying to get slot "Polygons" from an object of a basic class ("integer")
with no slots
rasterprojection2<- Polygons(rasterprojection)
Error in as.vector(x, "list") :
cannot coerce type 'S4' to vector of type 'list'
Essentially, all I need to do is to connect the coordinates into polygons.
What am I doing wrong?
You used readgdal to read the tif file. If you want polygons, get a
shapefile and read it using readOGR or readShapeLines or readShapePoly.
Thank you!
------------------------------------------------------------------------
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: +3130 274 3113 Mon-Tue
Phone: +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul
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