[R-sig-Geo] Transforming from cartographic to arbitrary local coordinate system
macq at llnl.gov
Mon Nov 19 22:27:13 CET 2007
I have virtually no experience with cartographic coordinate systems,
and transforming them, so I would like to ask for some help.
Someone has supplied me with a shapefile. When I open it in Qgis,
Qgis tells me its "spatial reference system" is:
+proj=lcc +lat_1=35.4666666666667 +lat_2=34.0333333333333
+lat_0=33.5 +lon_0=-118 +x_0=1999999.9371016 +y_0=499999.9843516001
+ellps=GRS80 +to_meter=0.3048006 +no_defs
I can read it into R using
tmp <- readShapeLines('filename',
where pstring is that thing that Qgis gave me.
plot(tmp) then gives a picture that makes sense.
I would like to give the thing a convenient (to me) local coordinate
system. I have quite a few such objects (all with the same proj.4
spatial reference string (or coordinate specification?). Some are
lines objects, some are polygon objects, and the polygon objects have
nested polygons ("holes" or "islands").
Pretend for the moment that the lines of my object represent borders
of a rectangular shaped plot of land . The rectangle is tilted
relative to north/south.
What I now would like to do is rotate and shift the rectangle so that
its borders appear vertical and horizontal (my local axes are
parallel to its borders), and so that it has a local origin near one
of the corners. I guess this isn't a true cartographic projection (?).
Is there a way I can do this with spTransform(), by supplying an
appropriate CRS argument?
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
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