Title: | Read and Write ESRI Shapefiles |
---|---|
Description: | Functions to read and write ESRI shapefiles. |
Authors: | Ben Stabler <[email protected]> |
Maintainer: | Ben Stabler <[email protected]> |
License: | GPL |
Version: | 0.7.2 |
Built: | 2024-11-01 06:38:10 UTC |
Source: | CRAN |
This package includes functions to read and write ESRI shapefiles.
read.shapefile(shape.name) read.shp(shp.name) read.shx(shx.name) read.dbf(dbf.name, header=FALSE) write.shapefile(shapefile, out.name, arcgis=FALSE) write.shp(shp, out.name) write.shx(shx, out.name) write.dbf(dbf, out.name, arcgis=FALSE) calc.header(shapefile) add.xy(shapefile) scaleXY(shapefile, scale.factor) convert.to.shapefile(shpTable, attTable, field, type) convert.to.simple(shp) change.id(shpTable, newFieldAsVector) dp(points, tolerance)
read.shapefile(shape.name) read.shp(shp.name) read.shx(shx.name) read.dbf(dbf.name, header=FALSE) write.shapefile(shapefile, out.name, arcgis=FALSE) write.shp(shp, out.name) write.shx(shx, out.name) write.dbf(dbf, out.name, arcgis=FALSE) calc.header(shapefile) add.xy(shapefile) scaleXY(shapefile, scale.factor) convert.to.shapefile(shpTable, attTable, field, type) convert.to.simple(shp) change.id(shpTable, newFieldAsVector) dp(points, tolerance)
shape.name |
String of the shapefile file name without an extension |
shp.name |
String of the shp file name with an extension |
shx.name |
String of the shx file name with an extension |
dbf.name |
String of the dbf file name with an extension |
shapefile |
The shapefile object of lists created by read.shapefile |
out.name |
Filename to write the data to |
shp |
shp portion (list) of the shapefile object of lists |
shx |
shx portion (list) of the shapefile object of lists |
dbf |
dbf portion (list) of the shapefile object of lists |
scale.factor |
Number to divide the shapefile geography by |
arcgis |
Replace "." with "_" in column names for ArcGIS |
shpTable |
data.frame with columns in order Id, X, and Y |
attTable |
data.frame with first column names "Id" - polygon id (key) |
type |
ESRI Shape type 1=point, 3=polyLine, 5=polygon |
field |
A field name in the attTable |
newFieldAsVector |
A vector of Ids to replace to the Ids in the shpTable |
points |
A named list of two vectors (x and y) representing points |
tolerance |
A tolerance setting for the DP polyLine simplification algorithm |
header |
Should read.dbf return the header? |
ESRI shapefiles consist of three files. The first file (*.shp) contains the geography
of each shape. The second file (*.shx) is an index file which contains record offsets.
The third file (*.dbf) contains feature attributes with one record per feature.
read.shapefile
calls read.shp, read.shx
, and read.dbf
to read
in an entire shapefile. The result of read.shapefile
is a list of many more
lists. The sublists are shp
, shx
, and dbf
. Each sublist contains
a header list and some sort of data list. The shp list is a list of
$shp$header
and $shp$shp
. The shx list is a list of
$shx$header
and $shx$index
. The dbf list is a list of
$dbf$header
and $dbf$dbf
.
The write functions write out a shp, shx, and dbf file from the shapefile list structure.
To write out a shapefile from simple R data, you need to run convert.to.shapefile
.
The inputs to this function are a simple data frame of points (for points, polyLines, or
polygons) and a data frame representing the dbf file. Examples are below.
The package reads shape types 1 (point), 3 (polyLine), 5 (polygon), 13 (polyLineZ),
and 15 (polygonZ). Reading of shape type 13 and 15 from Don MacQueen, [email protected]
The package writes shape types 1 (point), 3 (polyLine), 5 (polygon), 13 (polyLineZ),
and 15 (polygonZ). Conversion of simple polygons to shapefile format from Manuel
Chirouze, [email protected]
For simple features, the only difference between polyLines and polygons is that the first
and last point is the same for a polygon. The convert.to.simple
function
can be used to simplify the shp file to a simple data.frame. The change.id
function
can then be used to change the Id field for the simple shp data.frame to a field from
a data.frame (dbf).
For details about the ESRI shapefile structure refer to
https://www.esri.com/content/dam/esrisites/sitecore-archive/Files/Pdfs/library/whitepapers/pdfs/shapefile.pdf. A detailed description
of DBF files can be found at https://www.e-bachmann.dk/docs/xbase.htm. The arcgis
argument to write.dbf
replaces "." with "_" in field names since ArcGIS does not allow
the former. Note that the read.dbf
and write.dbf
functions in the foreign
package are now used for reading and writing dbfs, which greatly improves the speed of
reading/writing dbfs.
Function dp
is an implementation of the Douglas-Peucker polyLine simplification
algorithm. Douglas, D. and Peucker, T. (1973). "Algorithms for the reduction of the number
of points required to represent a digitized line or its caricature." The Canadian
Cartographer 10(2). 112-122. dp
currently uses the line, not the line segment to determine
the distance of the points from the line. This can result in the omission of extreme
"outlier-like" points. See doi:10.3138/FM57-6770-U75U-7727 for more information.
read.shapefile |
list | shapefile list object |
read.shp |
list | shp list object |
read.shx |
list | shx list object |
read.dbf |
list | DBF list object |
write.shapefile |
NA | Nothing returned |
write.shp |
NA | Nothing returned |
write.shx |
NA | Nothing returned |
write.dbf |
NA | Nothing returned |
calc.header |
list | shapefile list object |
add.xy |
list | shapefile list object |
scaleXY |
list | shapefile list object |
convert.to.shapefile |
list | shapefile list object |
convert.to.simple |
list | data.frame list data.frame |
change.id |
list | data.frame list data.frame |
dp |
list | data.frame list data.frame |
Ben Stabler <[email protected]>
## Not run: #Read entire shapefile shapefile <- read.shapefile("links") #Write entire shapefile write.shapefile(shapefile, "temp", T) #Read shp, shx, or dbf file dbf <- read.dbf("links.dbf") #Write shp, shx, or dbf file write.dbf(dbf, "links.dbf", T) #Calculate header (to clean up GeoMedia shapefile exports) shapefile <- calc.header(shapefile) #Add the X and Y coordinates to the dbf list of the shapefile list object shapefile <- add.xy(shapefile) #Scale the shapefile by scale.factor shapefile <- scaleXY(shapefile, scale.factor) #Samples of using the convert.to.shapefile function to write out simple shapefiles #from basic R data.frames #Point dd <- data.frame(Id=c(1,2),X=c(3,5),Y=c(9,6)) ddTable <- data.frame(Id=c(1,2),Name=c("Item1","Item2")) ddShapefile <- convert.to.shapefile(dd, ddTable, "Id", 1) write.shapefile(ddShapefile, "c:/test", arcgis=T) #PolyLine dd <- data.frame(Id=c(1,1,1,2,2,2),X=c(3,5,8,6,7,8),Y=c(9,8,3,6,7,4)) ddTable <- data.frame(Id=c(1,2),Name=c("Item1","Item2")) ddShapefile <- convert.to.shapefile(dd, ddTable, "Id", 3) write.shapefile(ddShapefile, "c:/test", arcgis=T) #Polygon dd <- data.frame(Id=c(1,1,1,1,2,2,2,2),X=c(3,5,8,3,6,7,8,6),Y=c(9,8,3,9,6,7,4,6)) ddTable <- data.frame(Id=c(1,2),Name=c("Item1","Item2")) ddShapefile <- convert.to.shapefile(dd, ddTable, "Id", 5) write.shapefile(ddShapefile, "c:/test", arcgis=T) #Convert to list of shapes ddAsList <- by(dd,dd$Id, function(x) x) #Convert to data.frame dd <- do.call(rbind, ddAsList) #Read in shp file and convert to simple format shpTest <- read.shp("c:/test.shp") simpleShpFormat <- convert.to.simple(shpTest) simpleShpFormat <- change.id(simpleShpFormat, c("a","b")) simpleAsList <- by(simpleShpFormat, simpleShpFormat[,1], function(x) x) backToShape <- convert.to.shapefile(simpleShpFormat, data.frame(index=c("a","b")), "index", 5) write.shapefile(backToShape, "c:/test", arcgis=T) #Polyline simplification with dp algorithm x <- c(5,3,4,1,8,9,10,11) y <- c(6,4,2,1,1,5,2,3) points <- list(x=x,y=y) plot(points, type="l") simpleLine <- dp(points, 2) lines(simpleLine, type="l", col="blue") ## End(Not run)
## Not run: #Read entire shapefile shapefile <- read.shapefile("links") #Write entire shapefile write.shapefile(shapefile, "temp", T) #Read shp, shx, or dbf file dbf <- read.dbf("links.dbf") #Write shp, shx, or dbf file write.dbf(dbf, "links.dbf", T) #Calculate header (to clean up GeoMedia shapefile exports) shapefile <- calc.header(shapefile) #Add the X and Y coordinates to the dbf list of the shapefile list object shapefile <- add.xy(shapefile) #Scale the shapefile by scale.factor shapefile <- scaleXY(shapefile, scale.factor) #Samples of using the convert.to.shapefile function to write out simple shapefiles #from basic R data.frames #Point dd <- data.frame(Id=c(1,2),X=c(3,5),Y=c(9,6)) ddTable <- data.frame(Id=c(1,2),Name=c("Item1","Item2")) ddShapefile <- convert.to.shapefile(dd, ddTable, "Id", 1) write.shapefile(ddShapefile, "c:/test", arcgis=T) #PolyLine dd <- data.frame(Id=c(1,1,1,2,2,2),X=c(3,5,8,6,7,8),Y=c(9,8,3,6,7,4)) ddTable <- data.frame(Id=c(1,2),Name=c("Item1","Item2")) ddShapefile <- convert.to.shapefile(dd, ddTable, "Id", 3) write.shapefile(ddShapefile, "c:/test", arcgis=T) #Polygon dd <- data.frame(Id=c(1,1,1,1,2,2,2,2),X=c(3,5,8,3,6,7,8,6),Y=c(9,8,3,9,6,7,4,6)) ddTable <- data.frame(Id=c(1,2),Name=c("Item1","Item2")) ddShapefile <- convert.to.shapefile(dd, ddTable, "Id", 5) write.shapefile(ddShapefile, "c:/test", arcgis=T) #Convert to list of shapes ddAsList <- by(dd,dd$Id, function(x) x) #Convert to data.frame dd <- do.call(rbind, ddAsList) #Read in shp file and convert to simple format shpTest <- read.shp("c:/test.shp") simpleShpFormat <- convert.to.simple(shpTest) simpleShpFormat <- change.id(simpleShpFormat, c("a","b")) simpleAsList <- by(simpleShpFormat, simpleShpFormat[,1], function(x) x) backToShape <- convert.to.shapefile(simpleShpFormat, data.frame(index=c("a","b")), "index", 5) write.shapefile(backToShape, "c:/test", arcgis=T) #Polyline simplification with dp algorithm x <- c(5,3,4,1,8,9,10,11) y <- c(6,4,2,1,1,5,2,3) points <- list(x=x,y=y) plot(points, type="l") simpleLine <- dp(points, 2) lines(simpleLine, type="l", col="blue") ## End(Not run)