README
¶
go-shp
Go library for reading and writing ESRI Shapefiles. This is a pure Golang implementation based on the ESRI Shapefile technical description.
Usage
Installation
go get github.com/jonas-p/go-shp
Importing
import "github.com/jonas-p/go-shp"
Examples
Reading a shapefile
// open a shapefile for reading
shape, err := shp.Open("points.shp")
if err != nil { log.Fatal(err) }
defer shape.Close()
// fields from the attribute table (DBF)
fields := shape.Fields()
// loop through all features in the shapefile
for shape.Next() {
n, p := shape.Shape()
// print feature
fmt.Println(reflect.TypeOf(p).Elem(), p.BBox())
// print attributes
for k, f := range fields {
val := shape.ReadAttribute(n, k)
fmt.Printf("\t%v: %v\n", f, val)
}
fmt.Println()
}
Creating a shapefile
// points to write
points := []shp.Point{
shp.Point{10.0, 10.0},
shp.Point{10.0, 15.0},
shp.Point{15.0, 15.0},
shp.Point{15.0, 10.0},
}
// fields to write
fields := []shp.Field{
// String attribute field with length 25
shp.StringField("NAME", 25),
}
// create and open a shapefile for writing points
shape, err := shp.Create("points.shp", shp.POINT)
if err != nil { log.Fatal(err) }
defer shape.Close()
// setup fields for attributes
shape.SetFields(fields)
// write points and attributes
for n, point := range points {
shape.Write(&point)
// write attribute for object n for field 0 (NAME)
shape.WriteAttribute(n, 0, "Point " + strconv.Itoa(n + 1))
}
Resources
Documentation
¶
Index ¶
- Constants
- func AttributeCount(sr SequentialReader) int
- func Attributes(sr SequentialReader) []string
- func ShapesInZip(zipFilePath string) ([]string, error)
- type Box
- type Field
- type MultiPatch
- type MultiPoint
- type MultiPointM
- type MultiPointZ
- type Null
- type Point
- type PointM
- type PointZ
- type PolyLine
- type PolyLineM
- type PolyLineZ
- type Polygon
- type PolygonM
- type PolygonZ
- type Reader
- func (r *Reader) Attribute(n int) string
- func (r *Reader) AttributeCount() int
- func (r *Reader) BBox() Box
- func (r *Reader) Close() error
- func (r *Reader) Err() error
- func (r *Reader) Fields() []Field
- func (r *Reader) Next() bool
- func (r *Reader) ReadAttribute(row int, field int) string
- func (r *Reader) Shape() (int, Shape)
- type SequentialReader
- type Shape
- type ShapeType
- type Writer
- type ZipReader
Constants ¶
const ( NULL ShapeType = 0 POINT = 1 POLYLINE = 3 POLYGON = 5 MULTIPOINT = 8 POINTZ = 11 POLYLINEZ = 13 POLYGONZ = 15 MULTIPOINTZ = 18 POINTM = 21 POLYLINEM = 23 POLYGONM = 25 MULTIPOINTM = 28 MULTIPATCH = 31 )
These are the possible shape types.
Variables ¶
This section is empty.
Functions ¶
func AttributeCount ¶
func AttributeCount(sr SequentialReader) int
AttributeCount returns the number of fields of the database.
func Attributes ¶
func Attributes(sr SequentialReader) []string
Attributes returns all attributes of the shape that sr was last advanced to.
func ShapesInZip ¶
ShapesInZip returns a string-slice with the names (i.e. relatives paths in archive file tree) of all shapes that are in the ZIP archive at zipFilePath.
Types ¶
type Box ¶
type Box struct {
MinX, MinY, MaxX, MaxY float64
}
Box structure made up from four coordinates. This type is used to represent bounding boxes
func BBoxFromPoints ¶
BBoxFromPoints returns the bounding box calculated from points.
func (*Box) Extend ¶
Extend extends the box with coordinates from the provided box. This method calls Box.ExtendWithPoint twice with {MinX, MinY} and {MaxX, MaxY}
func (*Box) ExtendWithPoint ¶
ExtendWithPoint extends box with coordinates from point if they are outside the range of the current box.
type Field ¶
type Field struct {
Name [11]byte
Fieldtype byte
Addr [4]byte // not used
Size uint8
Precision uint8
Padding [14]byte
}
Field representation of a field object in the DBF file
func DateField ¶
DateField feturns a Field that can be used in SetFields to initialize the DBF file. Used to store Date strings formatted as YYYYMMDD. Data wise this is the same as a StringField with length 8.
func FloatField ¶
FloatField returns a Field that can be used in SetFields to initialize the DBF file. Used to store floating points with precision in the DBF.
func NumberField ¶
NumberField returns a Field that can be used in SetFields to initialize the DBF file.
func StringField ¶
StringField returns a Field that can be used in SetFields to initialize the DBF file.
type MultiPatch ¶
type MultiPatch struct {
Box Box
NumParts int32
NumPoints int32
Parts []int32
PartTypes []int32
Points []Point
ZRange [2]float64
ZArray []float64
MRange [2]float64
MArray []float64
}
MultiPatch consists of a number of surfaces patches. Each surface path descries a surface. The surface patches of a MultiPatch are referred to as its parts, and the type of part controls how the order of vertices of an MultiPatch part is interpreted.
func (MultiPatch) BBox ¶
func (p MultiPatch) BBox() Box
BBox returns the bounding box of the MultiPatch feature
type MultiPoint ¶
MultiPoint is the shape that consists of multiple points.
func (MultiPoint) BBox ¶
func (p MultiPoint) BBox() Box
BBox returns the bounding box of the MultiPoint feature
type MultiPointM ¶
type MultiPointM struct {
Box Box
NumPoints int32
Points []Point
MRange [2]float64
MArray []float64
}
MultiPointM is the collection of multiple points with measures.
func (MultiPointM) BBox ¶
func (p MultiPointM) BBox() Box
BBox eturns the bounding box of the MultiPointM feature
type MultiPointZ ¶
type MultiPointZ struct {
Box Box
NumPoints int32
Points []Point
ZRange [2]float64
ZArray []float64
MRange [2]float64
MArray []float64
}
MultiPointZ consists of one ore more PointZ.
func (MultiPointZ) BBox ¶
func (p MultiPointZ) BBox() Box
BBox eturns the bounding box of the MultiPointZ feature.
type Point ¶
type Point struct {
X, Y float64
}
Point is the shape that consists of single a geometry point.
type PolyLine ¶
PolyLine is a shape type that consists of an ordered set of vertices that consists of one or more parts. A part is a connected sequence of two ore more points. Parts may or may not be connected to another and may or may not intersect each other.
func NewPolyLine ¶
NewPolyLine returns a pointer a new PolyLine created with the provided points. The inner slice should be the points that the parent part consists of.
type PolyLineM ¶
type PolyLineM struct {
Box Box
NumParts int32
NumPoints int32
Parts []int32
Points []Point
MRange [2]float64
MArray []float64
}
PolyLineM is the polyline in which each point also has a measure.
type PolyLineZ ¶
type PolyLineZ struct {
Box Box
NumParts int32
NumPoints int32
Parts []int32
Points []Point
ZRange [2]float64
ZArray []float64
MRange [2]float64
MArray []float64
}
PolyLineZ is a shape which consists of one or more parts. A part is a connected sequence of two or more points. Parts may or may not be connected and may or may not intersect one another.
type Polygon ¶
type Polygon PolyLine
Polygon is identical to the PolyLine struct. However the parts must form rings that may not intersect.
type Reader ¶
type Reader struct {
GeometryType ShapeType
// contains filtered or unexported fields
}
Reader provides a interface for reading Shapefiles. Calls to the Next method will iterate through the objects in the Shapefile. After a call to Next the object will be available through the Shape method.
func (*Reader) Attribute ¶
Attribute returns value of the n-th attribute of the most recent feature that was read by a call to Next.
func (*Reader) AttributeCount ¶
AttributeCount returns number of records in the DBF table.
func (*Reader) Next ¶
Next reads in the next Shape in the Shapefile, which will then be available through the Shape method. It returns false when the reader has reached the end of the file or encounters an error.
func (*Reader) ReadAttribute ¶
ReadAttribute returns the attribute value at row for field in the DBF table as a string. Both values starts at 0.
type SequentialReader ¶
type SequentialReader interface {
// Close() frees the resources allocated by the SequentialReader.
io.Closer
// Next() tries to advance the reading by one shape and one attribute row
// and returns true if the read operation could be performed without any
// error.
Next() bool
// Shape returns the index and the last read shape. If the SequentialReader
// encountered any errors, nil is returned for the Shape.
Shape() (int, Shape)
// Attribute returns the value of the n-th attribute in the current row. If
// the SequentialReader encountered any errors, the empty string is
// returned.
Attribute(n int) string
// Fields returns the fields of the database. If the SequentialReader
// encountered any errors, nil is returned.
Fields() []Field
// Err returns the last non-EOF error encountered.
Err() error
}
SequentialReader is the interface that allows reading shapes and attributes one after another. It also embeds io.Closer.
func SequentialReaderFromExt ¶
func SequentialReaderFromExt(shp, dbf io.ReadCloser) SequentialReader
SequentialReaderFromExt returns a new SequentialReader that interprets shp as a source of shapes whose attributes can be retrieved from dbf.
type Shape ¶
type Shape interface {
BBox() Box
// contains filtered or unexported methods
}
Shape interface
type Writer ¶
type Writer struct {
GeometryType ShapeType
// contains filtered or unexported fields
}
Writer is the type that is used to write a new shapefile.
func Append ¶ added in v0.1.1
Append returns a Writer pointer that will append to the given shapefile and the first error that was encounted during creation of that Writer. The shapefile must have a valid index file.
func Create ¶
Create returns a point to new Writer and the first error that was encountered. In case an error occurred the returned Writer point will be nil This also creates a corresponding SHX file. It is important to use Close() when done because that method writes all the headers for each file (SHP, SHX and DBF). If filename does not end on ".shp" already, it will be treated as the basename for the file and the ".shp" extension will be appended to that name.
func (*Writer) Close ¶
func (w *Writer) Close()
Close closes the Writer. This must be used at the end of the transaction because it writes the correct headers to the SHP/SHX and DBF files before closing.
func (*Writer) SetFields ¶
SetFields sets field values in the DBF. This initializes the DBF file and should be used prior to writing any attributes.
func (*Writer) Write ¶
Write shape to the Shapefile. This also creates a record in the SHX file and DBF file (if it is initialized). Returns the index of the written object which can be used in WriteAttribute.
func (*Writer) WriteAttribute ¶
WriteAttribute writes value for field into the given row in the DBF. Row number should be the same as the order the Shape was written to the Shapefile. The field value corresponds to the field in the slice used in SetFields.
type ZipReader ¶
type ZipReader struct {
// contains filtered or unexported fields
}
ZipReader provides an interface for reading Shapefiles that are compressed in a ZIP archive.
func OpenShapeFromZip ¶
OpenShapeFromZip opens a shape file that is contained in a ZIP archive. The parameter name is name of the shape file. The name of the shapefile must be a relative path: it must not start with a drive letter (e.g. C:) or leading slash, and only forward slashes are allowed. These rules are the same as in https://golang.org/pkg/archive/zip/#FileHeader.
func (*ZipReader) Attribute ¶
Attribute returns the n-th field of the last row that was read. If there were any errors before, the empty string is returned.
Source Files