This package provides classes for defining and applying both affine and similarity transformations on vector spatial data (sp objects). Transformations can be defined from control points or directly from parameters. If redundant control points are provided Least Squares is applied allowing to obtain residuals and RMSE.
| Package: | vec2dtransf |
| Type: | Package |
| Version: | 1.1 |
| Date: | 2012-04-09 |
| License: | GPL (>= 2) |
| Depends: | sp |
This package helps to define a transformation object (either similarity or affine) from control points or directly from parameters. Similarity transformations can rotate, shift and scale geometries whereas affine transformations can rotate, shift, scale (even applying different factors on each axis) and skew geometries.
If control points are provided, the 'calculateParameters' method must be used in order to calculate the transformation parameters. If there are more control points than required (2 for similarity and 3 for affine) Least Squares is applied and therefore residuals as well as Root Mean Square Error (RMSE) are available via 'getResiduals' and 'getRMSE' methods. Parameters can always be accessed via 'getParameters' method.
Once parameters are known, sp objects can be transformed by usign the 'applyTransformation' method. Supported sp objects are SpatialPoints, SpatialPointsDataFrame, SpatialLines, SpatialLinesDataFrame, SpatialPolygons and SpatialPolygonsDataFrame.
Additionally, the method 'plotGridTransformation' can plot a grid of points to see the effect of the transformation on a given extent.
Iliffe, J. and Lott, R. Datums and map projections: For remote sensing, GIS and surveying. Section 4.5. pp.109-117,135-137, 2008.
UC Davis Soil Resource Laboratory. Case Study: Fixing Bad TIGER Line data with R and PostGIS. <URL: http://casoilresource.lawr.ucdavis.edu/drupal/node/433>
Knippers, R. 2D Cartesian coordinate transformations. 2009. <URL: http://kartoweb.itc.nl/geometrics/Coordinate%20transformations/coordtrans.html>
Pebesma, E. and Bivand, R. sp package: <URL: http://cran.r-project.org/web/packages/sp/index.html>