[R] Problems generating image from tiff file

[Paul Hiemstra]

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.hiemstra at geo.uu.nl 
> <mailto:p.hiemstra at 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!
>          ------------------------------------------------------------------------
>
>
>
>         ______________________________________________
>         R-help at r-project.org <mailto:R-help at r-project.org> mailing list
>         https://stat.ethz.ch/mailman/listinfo/r-help
>         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>
>
>