Hi Mehdi,
No problem, we all have to start somewhere! Glad to have helped.
If you take a look at
http://wiki.r-project.org/rwiki/doku.php?id=tips:spatial-data:spatial_data_visualization
you will find some tips on how to plot spatial data using spplot.
Including how to plot a grid together with a polygon.
good luck and cheers,
Paul
Mehdi Khan schreef:
Paul,
Thank you very much for your explanation. I have only been using R
for GIS purposes for about a week, so my expertise in the field is
shallow. Your explanation helped me out and I was able to plot the
tif file simply by using the spplot command.
The reason I was projecting it was that I am trying to project a
separate shape file on top of the tif--and the coordinates of the two
files are different.
What I ended up doing was using spTransform to change the coordinate
system of the shape file into that of the tif file, and used the image
() and plot commands to graph them on top of one another.
I'm definately a novice when it comes to R, but I am learning. Thanks
a lot!
On Fri, Jul 17, 2009 at 12:25 AM, Paul Hiemstra <p.hiems...@geo.uu.nl
<mailto:p.hiems...@geo.uu.nl>> wrote:
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 <http://intamap.geo.uu.nl/%7Epaul>
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