[Qgis-user] Standard Deviational Ellipse

[gene]

It is very easy to do in R with aspace

  library(aspace)
  library rgdal
  # open the shapefile
  layer = readOGR("/Users/Shared",layer="points_test_aspace")
  coords=coordinates(layer)
  # calculate the ellipse
  calc_sde(id=1,points=coords) #you can add many parameters here as
calc_sde(id=1, filename="SDE_Output.txt", centre.xy=NULL, calccentre=TRUE, 
  weighted=FALSE, weights=NULL, points=coords, verbose=FALSE)
  # save the result to shapefile
  shp = convert.to.shapefile(sdeloc,sdeatt,"id",5)
  write.shapefile(shp, "SDE_Shape", arcgis=T)

aspace uses the package  shapefile
<https://cran.r-project.org/web/packages/shapefiles/>   to write the
shapefile (a polygon from points, parameter 5 in shp) and it needs an
intermediate file to store the coordinates (SDE_Output.txt here). 

But as the geometry (ellipse) is  stored in the sdeloc variable (points) and
the attributes in the sdeatt variable, you can make a processing rscript. 
In the script, you don't need the intermediate file because QGIS uses Rgdal
to read and write files but aspace needs it otherwise it doesn't work


    ##Ellipse=group
    ##Layer=vector
    ##Output = output vector
    library(aspace)
    coords<-coordinates(Layer)
    calc_sde(id=1, filename="/Users/me/SDE_Output.txt", centre.xy=NULL,
calccentre=TRUE, weighted=FALSE, weights=NULL, points=coords, verbose=FALSE)
    fin_coord = c(sdeloc[2],sdeloc[3])
    # directly transform the points to a SpatialPolygonsDataFrame
    sp = SpatialPolygons( list(Polygons(list(Polygon(fin_coord )), 1)))
    res = SpatialPolygonsDataFrame(sp, sdeatt)
    Output<-res

There are many other variables in the resulting attribute table that you can
use (cendroid, theta angle, etc.)

<http://osgeo-org.1560.x6.nabble.com/file/n5267523/ellipse.png> 



--
View this message in context: http://osgeo-org.1560.x6.nabble.com/Standard-Deviational-Ellipse-tp5267195p5267523.html
Sent from the Quantum GIS - User mailing list archive at Nabble.com.