Odin ShapeLib

version (v1.1, Nov 2025)

This Odin library is written to support export and import from ESRI Shape files. Only two-dimensional features are supported in this version.

Map projections is supported, but limmited to EPSG-codes.

See also the Shapefile C Library

Changes

• v1.1 (Nov, 2025): Added support for .prj files.

Importing the library

import "shp"

Or the path to the library directory.

Types

ShpHandle

ShpHandle :: struct {
    ...
}

Keeps track of the files and read/write state.

ShapeType

ShpType :: enum {
    null = 0,
    point = 1,
    line = 3,       // same as polyline
    area = 5,       // same as polygon
    multiPoint = 8,

    // not supported:
    pointZ = 11,  
    lineZ = 	13,
    areaZ = 15,
    multiPointZ = 18,
    pointM = 21,
    lineM = 23,
    areaM = 25,
    multiPointM = 28,
    multiPatch = 31
}

To get the shape type from a shape handle:

get_shape_type :: proc( handle :^ShpHandle) -> ShpType

ShpObject

Holds a single object or feature:

ShpObject :: struct #packed {
    shpType   : i32le,
    box       : [4]f64le,
    numParts  : i32le,
    numPoints : i32le,
    parts     : [dynamic]i32le,
    coords    : [dynamic]ShpPoint,	// points
    attrs     : [dynamic]DbfValue
}

ShpValState

Used to return a state when you request an attribute value from an object

ShpValState :: enum {
    ok,
    null,           // the attribute is nill
    incompatible    // e.g. if you request an int from an attribute that is a string
}

Constants

Database field types

dbfStringAttribute  :: u8('C')
dbfNumberAttribute  :: u8('N')
dbfDateAttribute    :: u8('D')
dbfFloatAttribute   :: u8('F')

Procedures

Open Existing Files

Open for reading:

open_files :: proc( filePath : string) -> (^ShpHandle, os.Error)

Reading Objects

read_first_obj :: proc( handle :^ShpHandle) -> (^ShpObject, os.Error)
read_obj :: proc( handle :^ShpHandle, index : int) -> (^ShpObject, os.Error)
read_next_obj :: proc( handle :^ShpHandle) -> (^ShpObject, os.Error)

Get Object Coordinates

get_point_xy :: proc ( obj :^ShpObject) -> (f64, f64)

Asserts that obj is of type ShpType.point

get_parts ::proc( obj :^ShpObject) -> [dynamic][dynamic][2]f64
delete_parts :: proc (parts :[dynamic][dynamic][2]f64)

Asserts that obj is NOT of type ShpType.point

Get Attribute Defintions

get_field_count :: proc( handle :ShpHandle) -> int
get_field_name :: proc( handle :ShpHandle, index :int) ->string
get_field_type :: proc( handle :ShpHandle, index :int) ->u8
get_field_size :: proc( handle :ShpHandle, index :int) ->(u8, u8)
    // returns width, decimals
get_field_definition :: proc( handle :ShpHandle, index :int) ->(string, u8, u8, u8)
    // returns name, type, width, decimals 

Get Object Attribute Values

get_string_value :: proc( obj :^ShpObject, attrIndex : int) -> (string, ShpValState)
get_int_value :: proc( obj :^ShpObject, attrIndex : int) -> (int, ShpValState)
get_float_value :: proc( obj :^ShpObject, attrIndex : int) -> (f64, ShpValState)
get_date_value :: proc( obj :^ShpObject, attrIndex : int) -> (time.Time, ShpValState)
is_null_value :: proc( obj :^ShpObject, attrIndex : int) -> bool

Create new Files

Open for write, will always create new files, overwriting existing ones.

create_files :: proc( filePath : string, shpType :ShpType, epsgCode: string = "") -> (^ShpHandle, os.Error)

Adding database fields:

add_field :: proc( handle :^ShpHandle,
                   name : string, 
                   type : u8, // dbf... constants
                   width : u8 = 0, 
                   decimals : u8 = 0)

This must be done before writing objects to the files

Closing Files

close_and_dispose :: proc (handle : ^^ShpHandle)

Closes the files, and frees the memory. Sets the handle to nil.

Creating Objects

create_obj :: proc ( shpType : ShpType) -> ^ShpObject

You must add all attributes to the record, the number of values added must be the same as the number of attribute fields added.

add_string_value :: proc ( obj :^ShpObject, strValue : string)
add_int_value :: proc ( obj :^ShpObject, intValue : int)
add_float_value :: proc ( obj :^ShpObject, floatVal : f64)
add_date_value :: proc ( obj :^ShpObject, date : time.Time)
add_null_value :: proc ( obj :^ShpObject)

Setting coordinates of point object:

set_point_xy :: proc( obj: ^ShpObject, x, y: f64)

Adding coordinates of other shape types

add_part :: proc( obj: ^ShpObject, xyData :[][2]f64)
add_hole :: proc( obj: ^ShpObject, xyData :[][2]f64)

You can only add holes to area shapes, and you cannot add a hole unless you've added a part first.

xyData is an array of x and y pairs.

Dispose Objects

dispose_obj :: proc( obj : ^^ShpObject)

To free memory of object and set obj to nil

Write Objects

write_obj :: proc( handle :^ShpHandle, obj: ^ShpObject) -> os.Error

Get the Coordinate Reference System

get_epsg_code :: proc( handle :^ShpHandle) -> (string, ok: bool)

If the .prj file contains an AUTHORITY element with the EPSG-code, returns the code with ok = true if exists, but ok = false if an EPSG-code is not found, despite the fact that there is a .prj-file.

Examples

Reading From a File

import "<path to shp>"

read_shape_file proc :: (filePath :string)
{
    handle, err := shp.open_files( filePath)
    assert (err == nil)
    defer shp.close_and_dispose( &handle)

    obj : ^shp.ShpObject
    obj, err = shp.read_first_obj( handle)
    for err == nil {
        do_something( obj)
		shp.dispose_obj( &obj)
		  
        obj, err = shp.read_next_obj( handle)
    }
}

Writing to a new File

import "<path to shp>"
import "core:time"

write_to_file proc :: (filePath :string)
{
    handle, err := shp.create_files( filePath, shp.ShpType.point, "EPSG:4326")
    defer close_and_dispose( &handle)
    assert( err == nil)

    shp.add_field( handle, "id", shp.dbfNumberAttribute, 5)
    shp.add_field( handle, "name", shp.dbfStringAttribute, 12)
    shp.add_field( handle, "area", shp.dbfNumberAttribute, 15, 2)
    shp.add_field( handle, "date", shp.dbfDateAttribute)

    obj := shp.create_obj( shp.ShpType.point)
    defer shp.dispose_obj( &obj)
    assert(obj != nil)

    shp.add_int_value( obj, 123)                // id
    shp.add_string_value( obj, "Trondheim")     // name
    shp.add_float_value( obj, 342.2)            // area (sq.km)
    shp.add_date_value( obj, time.now())        // date

    shp.set_point_xy( obj, 10.395916, 63.433412)  // only for point features
    // shp.add_part(...) for other types.
    // shp.add_hole(...) to add holes in polygon

    err = shp.write_obj( handle, obj)
    assert( err == nil)
}

Author

Agnar Renolen agnar.renolen@gmail.com