How to Read Layer and Linetype in Autocad Vb.net
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Problem and Solution
Software development in industry, edifice and many other fields requires working with CAD drawings. The well-nigh popular CAD formats are AutoCAD DWG and AutoCAD DXF, the latter being "simplified" dwg - a special format to be used past developers. The trouble is that DXF and DWG formats are actually complicated. They accept dozens of objects with hundreds of interaction tricks and thousands of properties. Official DXF Reference from Autodesk has 256 pages though it fails to draw many important facts. Hence, the evolution for CAD drawings is frequently required but is not easy to implement. This commodity is to tell you how to write the DXF reader in C#, what problems can arise and of course you can observe case in C# source lawmaking, which is costless for employ under MPL license.
DXF Construction
DXF is an open up ASCII format from Autodesk and you can hands find documentation on information technology in the web. Here are some words about it. Below is a very unproblematic example, to show the main parts:
0 SECTION 2 ENTITIES 0 LINE 10 39.19953392043317 xx 36.4554281665769 xxx 0.0 11 39.19953392043322 21 736.4554281665768 31 0.0 0 ENDSEC 0 EOF
0 - introduction of extended symbol names, following the "0"
Section, ENDSEC - begin / terminate of section. Sections can include Header, Entities, Objects. In the above code, you lot see just Entities section where the entities are.
LINE - begins LINE entity description. Lines:
10 39.19953392043317
hateful X1 double value. The value afterward 20 is Y1, later on 30 - Z1 (0 in 2nd drawings). 11, 21 and 31 codes are consequently for X2, Y2, Z2. Then here we run across the line with coordinates (39.19.., 36, 45.. - 39,19.., 736,45..) - this is vertical line.
Then our aim is to read this ASCII format. We need to load the file to stream and to have lines - even lines (0, 2, 4..) are Code, odd lines (1, 3, v...) are VALUE and repeat this procedure step by step till the end of file "EOF".
public void Next() { FCode = Convert.ToInt32(FStream.ReadLine()); FValue = FStream.ReadLine(); } public DXFEntity CreateEntity() { DXFEntity E; switch (FValue) { case " ENDSEC": render null; case " ENDBLK": return nothing; case " ENDTAB": render aught; case " LINE": East = new DXFLine(); pause; example " SECTION": E = new DXFSection(); pause; case " BLOCK": Due east = new DXFBlock(); suspension; example " INSERT": E = new DXFInsert(); intermission; case " TABLE": Due east = new DXFTable(); break; case " Circumvolve": E = new DXFCircle(); break; case " LAYER": E = new DXFLayer(); break; case " TEXT": Due east = new DXFText(); break; case " MTEXT": Due east = new DXFMText(); pause; example " ARC": Due east = new DXFArc(); break; case " ELLIPSE": E = new DXFEllipse(); interruption; default: E = new DXFEntity(); break; } E.Converter = this; render E; }
The method to read properties of entities is essentially similar to the ane described to a higher place but information technology has one important point: different entities have both identical and different properties. For case, many Entities take "base bespeak" - in DXF, which is described by codes: x (x), 20 (y), thirty(z):
LINE x 39.19953392043317 xx 36.4554281665769 thirty 0.0
These codes are the aforementioned for LINE, Circumvolve, ELLIPSE, TEXT and for many others. So nosotros tin make Object-Oriented construction to read and to store the backdrop in order to avoid double-coding. We will shop Layer and Base Point in entity "DXFVisibleEntity" which will be ancestor for all visible entities. Look at the lawmaking to read these properties:
public form DXFVisibleEntity : DXFEntity { public DXFImport.SFPoint Point1 = new SFPoint(); public override void ReadProperty() { switch (Converter.FCode) { case eight: layer = Converter.LayerByName(Converter.FValue); break; instance 10: Point1.X = Convert.ToSingle(Converter.FValue, Converter.N); suspension; case 20: Point1.Y = Convert.ToSingle(Converter.FValue, Converter.N); break; case 62: FColor = CADImage.IntToColor(Convert.ToInt32(Converter.FValue, Converter.N)); break; } } }
We use the same approach to read the 2d coordinate in LINE, radius in Circumvolve and so on.
DXF File and DXF Import .Internet Construction
This scheme shows main parts of DXF file and the way they are connected with the C# source lawmaking in the project. The dash lines stand for associations betwixt DXF file objects and objects, programmed in C#.
CADImage is a class for loading from DXF file and drawing to Graphics. Information technology stores the DXF Entities in field:
public DXFSection FEntities; In the scheme, it is DXFSection.
DXFEntity is base of operations course for all Entities classes. Classes DXFBlocks and DXFSection are not visible. Class DXFVisibleEntity is the antecedent for all visible Entities.
Past the manner, the scheme above is made in DXF format:) in ABViewer software.
CAD Tricks
If you are not familiar with AutoCAD, please pay attention to the structure of DXF entities. There is a special entity "Block" which may accept many "inserts" in the CAD drawing. Block is merely set of entities (including nested blocks) which can be inserted many times.
Annotation
Block changes many backdrop of element when showing information technology. And then if you want to know the color of entity, it is not enough to read "Entity.Colour" - it is necessary to see all the Inserts and Blocks, in which this entity tin be included. To get the right color in DXF Import .NET project nosotros fabricated the post-obit function: EntColor(DXFEntity E, DXFInsert Ins).
Delight use EntColor() function go the correct Color blazon fifty-fifty if you do non have Blocks in the file. Pay attention that the most common color is "ByLayer" and in social club to read the correct color, we need to read the color from Layer entity. This functionality is also provided in this role.
Below is the EntColor function. Information technology has many tricks, for instance checking the layer.proper noun == "0" - in DXF layer "0" is special and elements with colour "ByLayer" get the color from Cake if they are on "0" layer.
public static Color EntColor(DXFEntity Eastward, DXFInsert Ins) { DXFInsert vIns = Ins; DXFEntity Ent = E; Colour Upshot = DXFConst.clNone; if(Ent is DXFVisibleEntity) Result = E.FColor; if(E.layer == naught) return Issue; if((Result == clByLayer)||(Consequence == clByBlock)) { if((vIns == goose egg)||((Consequence == clByLayer)&&(Ent.layer.proper noun != " 0"))) { if(Effect == clByLayer) { if(Ent.layer.color != clNone) Issue = Ent.layer.color; else Outcome = Color.Blackness; } } else { while(vIns != zippo) { Result = vIns.color; if((Result != clByBlock) && !((Outcome == clByLayer) && (vIns.layer.name == " 0"))) { if(Result == clByLayer) Effect = vIns.layer.color; break; } if((vIns.owner == null)&&(Outcome == clByLayer)) Result = vIns.layer.color; vIns = vIns.possessor; } } } if((Result == clByLayer)||(Result == clByBlock)) Result = clNone; return Event; }
How to Use the Software
The principal code is in DXFImport.cs. You can only use this file in your project or meet to it every bit an instance of reading and visualization of DXF files.
Sample code to apply DXFImport.cs is Form1.cs.
How to View Entities
In Form1.cs, we use the Form1_Paint event:
private void Form1_Paint(object sender, Arrangement.Windows.Forms.PaintEventArgs e) { if (FCADImage == null) return; FCADImage.Draw(e.Graphics); }
We can use FCADImage.Depict() for cartoon to any Graphics - for instance, to printer. FCADImage.Draw() function should utilize a special algorithm, when each entity is drawn with the use of block/insert/layer parameters.
public void Describe(Graphics east) { if (FMain == aught) return; FGraphics = eastward; FEntities.Iterate(new CADEntityProc(DrawEntity), FParams); }
Pay attention to FEntities.Iterate() func, it allows accessing all entities including their being within the blocks. This is how information technology works: There is a class DXFGroup which is an ancestor of Entity and which can shop array of Entities. For instance, Block is antecedent of DXFGroup and tin can store many entities like LINE. For amend unification, we tin use ONE BASE GROUP ENTITY object for all the drawing, this Entity will have array of all entities, each of them can besides exist the Grouping - the archetype "Tree".
Iterate method finally should call Describe() for each Entity in order to describe it to the Graphics:
protected static void DrawEntity(DXFEntity Ent) { Ent.Depict(FGraphics); }
Depict() method is overridden in descendants of Entity to draw particular entities. Let us see in particular how it is implemented in DXFLine:
public override void Draw(System.Drawing.Graphics G) { SFPoint P1, P2; Colour RealColor = DXFConst.EntColor(this, Converter.FParams.Insert); P1 = Converter.GetPoint(Point1); P2 = Converter.GetPoint(Point2); if (FVisible) G.DrawLine(new Pen(RealColor, one), P1.Ten, P1.Y, P2.10, P2.Y); }
- We get the Real Color via
DXFConst.EntColor(this, Converter.FParams.Insert);equally I described earlier. - Points are converted from Global Coordinates to screen coordinates in part
GetPoint().GetPointnot only converts global-to-screen but too usesBlockoffsets and cake scale inside. Thus it facilitates the evolution work, eliminating the demand to "encounter" what cake is being drawn at the moment - Cake changes "FParams.matrix" to draw itself. And all entities coordinates use this "FParams.matrix". - Entity is fatigued to the given
Graphics 1000:
Then y'all can describe to printer, to raster image or to other Graphics.
DXF Import .NET Reference
public class DXFConst
Stores constants and base functions.
public class DXFMatrix
Class to work with coordinates.
public struct FRect
Description of 3D space where the CAD drawing is situated in global coordinates.
public struct CADIterate
Stores all needed parameters for entities when processing "Iterate" function.
public course CADImage
Class to draw CAD drawing.
public grade DXFEntity
Base class for all DXF Entities.
public class DXFGroup : DXFEntity
Base of operations form for all grouping entities.
public class DXFTable : DXFGroup
Class to read from DXF "Tabular array" section - here it reads only Layers.
public class DXFVisibleEntity : DXFEntity
Base course for all visible entities (invisible - are "DXFTable", "DXFLayer", etc.)
public class DXFCustomVertex: DXFVisibleEntity
Special class for 3D point in DXF.
public class DXFText: DXFCustomVertex
Stores and Draws "Text" DXF entity.
The following classes are for particular DXF entities:
public class DXFLine : DXFVisibleEntity public class DXFArc: DXFCircle public class DXFEllipse: DXFArc public form DXFLayer: DXFEntity
public class DXFBlock : DXFGroup
Form to work with DXF Block.
public class DXFInsert : DXFVisibleEntity
Class to work with "Insert" in DXF, for AutoCAD users this is "Block reference". Blocks are not visible, Inserts are visible.
Conclusion
The purpose of the article is to requite some communication how to write DXF readers. DXF file structure is non and then hard equally its logical presentation. The article looks through the base of operations DXF format problems and shows how to observe solution for them. The instance source is written in C# and may be helpful for all who demand to have access to DXF files.
Other Projects on The Code Project
On The Code Project, you can already find some other DXF reader:
- http://www.codeproject.com/KB/cs/dxfreader.aspx
The principal advantages of our project as compared to the project to a higher place are:
- Block / Inserts
- Layers
- Text
which are not presented in that DXF reader.
History
This is the first open source version of DXF Import .NET.
Source: https://www.codeproject.com/Articles/156522/DXF-Import-NET-Read-and-View-AutoCAD-Format-Files
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