Application: gvSIG desktop

jdwglib Developer's Guide

Overview

The Java DWG Library (jdwglib) is a Java libray designed for reading, handling and

writing drawing files in the Autodesk DWG format. This document is the design

specification for the classes, methods and algorithms implemented in the Java DWG

Library.

jdwglib has two different parts, first for DWG file accesing, and second for DWG file

handling. The part for accesing DWG files support the reading of DWG files and in

future versions we hope that writing of DWG files will be supported too. The part for

handling DWG files is designed for managing DWG complex objects like polylines or

blocks with the objective that the spatial position and the attributes of DWG objects

will be definitive and no one operation is required for obtaining the same results

that Autocad.

The detailed documentation of the class hierarchy and methods will be presented in the

form of JavaDoc for the source code.

Other resources

- Pythoncad DWG Library by Art Haas (www.pythoncad.org). The part of jdwglib that reads

  DWG files is a port of this library with an object oriented model added.

- The AutoCAD R13/R14/R2000 DWG File Specification by the OpenDWG Alliance. This is the

  public specification of the DWG format obtained using reverse engineering methods by

  the OpenDWG Alliance (www.opendwg.org).

Handling DWG files

jdwglib has been developed to allow GPL GIS applications to handle the information

stored in DWG files.

jdwglib has been designed to allow developers to create DWG drivers for their

CAD/GIS applications easily and in a GPL environment.

The use of jdwglib for any driver is ever the same:

- DwgFile dwgFile = new DwgFile(dwg.getAbsolutePath()); Creates a new DwgFile

  object for reading a DWG file.

- dwgFile.read(); Reads the DWG file but don't configure its objects.

- dwgFile.initializeLayerTable(); Creates a table with the DWG file layer

  information.

- dwgFile.calculateGisModelDwgPolylines() or dwgFile.calculateCadModelDwgPolylines();

  calculateGisModelDwgPolylines() configures Polyline's geometry. In Polylines with

  arcs, these arcs are defined by a set of points and a distance between these points.

  calculateCadModelDwgPolylines() configures Polyline's geometry. In Polylines with

  arcs, these arcs are defined by a curvature parameter called bulge that is associated

  with the points.

- dwgFile.applyExtrusions(); The extrusion parameters of the objets in a DWG file

  changes the location of these objects.

- dwgFile.testDwg3D(): test if the DWG file has elevation information.

- dwgFile.blockManagement(); This method manages the blocks contained in a DWG file.

- Vector dwgObjects = dwgFile.getDwgObjects(); Import the set of DWG objects. Now they

  are correctly configured.

- for (int i=0;i<dwgObjects.size();i++) {

			DwgObject iObj = (DwgObject)dwgObjects.get(i);

			if (iObj instanceof DwgArc) {

				//Convert iObj to the corresponding object model

			}

  } Convert DWG objects to the corresponding object model.

- String layerName = dwgFile.getLayerName(iObj); Returns the layer name of a DWG

  object.

- int colorByLayer = dwgFile.getColorByLayer(iObj); Returns color of the layer of a

  DWG object.

The author has implemented a DWG driver for gvSIG based on this library, and a DWG

driver for other Java GIS application like Jump or uDig must be easy to implement too.