Cloudv-tools NPM

Ginkgoch Shapefile

This is a NodeJs library to help to read/write Shapefile from your disk. API Reference.

Feature List

Query records from Shapefile
Append new records into Shapefile
Update a specified record in Shapefile
Remove a record
Create an empty Shapefile by a specified shape type.

Tutorial

Prerequisite

Node.js installed in your machine.
Install ginkgoch-shapefile package.

yarn add ginkgoch-shapefile

Code template for querying

In this section, we are going to operate the Shapefile. Before kick off, we need to open the shapefile in case we have everything prepared. We provide three ways to open the shapefile. Choose either one as you use to. 1. Regular way

```typescript
const statesShp = new Shapefile('./tests/data/USStates.shp');
statesShp.open();

// put your business logic here.

statesShp.close();
```

Fluent way to open

const statesShp = new Shapefile('./tests/data/USStates.shp').open();

// put your business logic here.

statesShp.close();

Callback way to open (auto close when callback complete)

const statesShp = new Shapefile('./tests/data/USStates.shp').openWith(() => {
    // put your business logic here.
});

Query Records

In this section, we are going to show you how to iterate shapefile records, get a specific record by id, and how to work with querying filters.

Query record by id

Let's start from a normal case - get record by id.

const statesShp = new Shapefile('./tests/data/USStates.shp').open();
const record = statesShp.get(1); // all ids are started from 1.

| Note: record is a structure formed with geometry and properties.

Get all records

This method fetches all records at once.

const records = statesShp.records();
console.log(records.length);

Iterate records

In previous section, we get all the records at once. It is convenient but it will take much memory usage for sure. Iterator allows to get all features in another way to get records one after another.

const iterator = statesShp.iterator();
let record = undefined;
while ((record = iterator.next()) && !iterator.done) {
    console.log(record);
}

Use filter

We allow to filter the records by following conditions. 1. from - The start id of the record to fetch. Default is 1. 1. limit - The limited record count to fetch. Default is Number.Max. 1. envelope - The envelope structure that all the records within will be fetched. e.g. { minx: -180, miny: -90, maxx: 180, maxy: 90 }. 1. fields - The fields to fetch from dbf file. Options are: - undefined - Not defined, by default, all fields will be fetched. - all - Same as undefined. - none - Ignore the dbf querying. - string[] - A specified field name list to fetch. e.g. ["RECID", "NAME"].

Here is a demo to fetch records from id 10 to 19, properties include RECID and STATE_NAME.

const records = statesShp.records({ from: 10, limit: 10, fields: ['RECID', 'STATE_NAME'] });

Code template for editing

Before appending new record, we need to do a little change before opening the Shapefile. Specify the file flag to 'rs+' or whatever flags to allow the file is able to edit.

const shapefile = new Shapefile(filePath, 'rs+');
shapefile.open();

// put your business logic here.

shapefile.close();

Append new record

A record is named as Feature in Ginkgoch. Let's create a feature first. Then push this feature into shapefile instance. Then Done.

const feature = new Feature(new Point(0, 0), { NAME: 'Tokyo', POP: 1.268 });
shapefile.push(feature);

Update a record

Updating a record is similar as appending a new record. The only difference is that, the feature to update requires a valid id.

const feature = new Feature(new Point(0, 0), { NAME: 'Tokyo', POP: 1.268 }, 1 /* the record id to update */);
shapefile.update(feature);

Remove a record

Specify an id to delete.

shapefile.remove(1); // remove the record whose id is 1.

Create new shapefile

To create a new shapefile, we need to prepare the following factors. 1. The new shapefile path to store. 1. The shape type to contain inside. Options are: point, polyLine, polygon and multiPoint. 1. The fields info.

const fields = new Array<DbfField>();
fields.push(new DbfField('RECID', DbfFieldType.number));
fields.push(new DbfField('NAME', DbfFieldType.character, 10));

const shapefile = Shapefile.createEmpty(filePath, ShapefileType.point, fields);
// here the shapefile instance is created with flag 'rs+'. Call open() method to continue appending new records.