[R-sig-Geo] Calculating the length of a line created from a spatial intersect.

[Walter Anderson]

Robert,

Thank you and I apologize.  I was trying the intersect command that you
used below (with the other material).

Specifically

result <- intersect(buffered_projects, road_centerline)

which only contained attributes from the buffered projects (ie no road
attributes).  I also tried it the other way,

result <- intersect(road_centerline, buffered_projects)

and this only had the attributes from the road (ie no project attributes).

When I performe the above intersection operation with ESRI I get both
attribute tables, ie

PROJECT	ROAD_NAME VOLUME
...

Which allow me to perform my calculations using the road data by project.

Since your example is using the same approach I was trying can you give
me some insight into what I am doing wrong?

Walter Anderson

On 04/01/2015 12:36 PM, Robert J. Hijmans wrote:
> Walter,
> 
> Next time, please try to give as a simple self contained example in R
> showing what you have done, and where you are stuck.
> 
> Here is how you can intersect lines and polygons, keeping their attributes:
> 
> library(raster)
> library(rgeos)
> 
> # example data
> p <- shapefile(system.file("external/lux.shp", package="raster"))
> 
> k1 <- (rbind(c(5.5, 49.6), c(6.5, 49.6)))
> k2 <- (rbind(c(5.5, 50), c(6.5, 50)))
> k <- SpatialLines(list(Lines(list(Line(k1)), "1"),  Lines(list(Line(k2)), "2")))
> k <- SpatialLinesDataFrame(k, data.frame(LID=1:2))
> crs(k) <- crs(p)
> 
> # intersection
> x <- intersect(k, p)
> 
> ## note that   x <- intersect(p, k)
> ## currently does not work; I'll fix that.
> 
> x
> data.frame(x)
> 
> Robert
> 
> On Wed, Apr 1, 2015 at 8:18 AM, Walter Anderson <wandrson01 at gmail.com> wrote:
>> Hello all,
>>
>> I am continuing on the process of automating an analysis that I
>> developed with ArcInfo using R with the sp, rgdal, rgeos, and raster
>> libraries.
>>
>> This step is similiar to my previous question concerning calculating the
>> area of a polygon created from a spatial intersect; however, the command
>> I was referred doesn't perform the merge of the two data frames as it
>> does when both spatial data sets are polygons.
>>
>> Here is the process I am using in ArcInfo that I need to replicate:
>>
>> I have a shape file (lines) that defines the limits of all of the
>> projects with each project having a unique identifier.
>>
>> I have another shape file (lines) that represent the road centerlines
>> and have a traffic volumen associated with each link.
>>
>> Process
>> Step 1.
>> I then buffer these project lines to create a second shape file that
>> represents the 'footprint' of the project. (Creates polys).  This is a
>> small footprint (250 ft) that is solely used to associate the
>> appropriate portion of any adjacent roadways.  Mostly to accomodate
>> spatial errors...
>>
>> Step 2.
>> In ArcInfo, I perform an intersection of the two shape files
>> (footprint and roadway centerlines) and this creates a third shape file
>> which has a unique line for every project buffer/roadway intersection.
>> This attribute table contains the attributes from both original shape files
>>
>> Step 3.
>> I then perform a calculation that provides a weighted volume to
>> associate with each project.  The weighting is based upon the lengths of
>> the road segments that are 'cut' by the project in relation to their
>> original lengths.
>>
>> My issue is that I have not found a method to 'intersect' the two
>> spatial data sets and retain both of their attributes (and calculate new
>> lengths).
>>
>> Walter Anderson
>>
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>