SWMM5 Delphi GUI Udxf.pas Summary

 Expanded Summary of Udxf.pas

This Delphi Pascal unit Udxf.pas is responsible for exporting the SWMM study area map to a DXF (Drawing Exchange Format) file. It uses various drawing primitives (lines, circles, polylines, text, etc.) to represent nodes, links, subcatchments, and labels from an EPA SWMM model in a DXF file that can be opened in a CAD application.

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1. Purpose & Usage

• Main Entry Point:

  procedure DXFexport(const fname: String; const Jstyle: Integer);
  

  This is the procedure that the rest of the SWMM code calls to export all visual elements of the model (e.g., subcatchments, nodes, links, labels) into a DXF file named fname. The parameter Jstyle indicates how junction nodes will be drawn (e.g., as circles, crosses, squares, etc.).

• DXF Format:
  The code writes plain-text lines in the correct order and structure to a .dxf file. The content is broken up into:

  1. Header (map extents).
  2. Tables (line types, layers, etc.).
  3. Entities (actual geometry).

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2. DXF Data Structures & Outline

1. Header

   • The procedure AddHeader(...) writes out $EXTMIN and $EXTMAX to define the bounding box extents in the DXF file.

2. Layer Table

   • StartTables(Nlayers) writes the starting lines of the DXF TABLES section with N layers.
   • AddLayer(LayerName, ColorIndex) is called for each separate layer (e.g., “Subcatchments,” “Links,” “Nodes,” “Arrows,” “Labels”).
   • EndTables closes the layer table and begins the SECTION ENTITIES block.

3. Entities

   • Various geometry elements are added:
     • Circle (for nodes, if style is set to circles).
     • Polyline (for subcatchment polygons, link polylines).
     • Line or Solid (for arrowheads or node shapes).
     • Text (for labels).

4. Ending the File

   • EndDXF writes the ENDSEC and EOF lines required at the end of the DXF.

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3. Key Procedures

3.1. DXFexport(const fname: String; const Jstyle: Integer)

• Input:

  1. fname: name of the resulting DXF file on disk.
  2. Jstyle: node-drawing style (e.g., circle, cross, etc.).

• Actions:

  1. Open a text file for writing (DXFfile).
  2. Retrieve information from SWMM:
     • The “Map” instance (with subcatchments, nodes, etc.).
     • Various map styling options (line sizes, arrow sizes, etc.).
  3. Compute or look up color indexes for subcatchments, links, and nodes. (DXF color is integer-based, so the code finds the “closest” integer color index from a set.)
  4. Write the DXF “header” with bounding box extents.
  5. Create table data: layers for subcatchments, links, nodes, arrows, labels.
  6. Iterate over each object in the SWMM model:
     • Subcatchments: add them as polylines.
     • Links: add polylines plus optional arrowheads.
     • Nodes: add circles or squares or crosses, depending on Jstyle.
     • Labels: add text items.
  7. Finish by writing end-of-file markers.

3.2. AddHeader(xmin, ymin, xmax, ymax: Single)

• Writes out the minimal bounding rectangle that the CAD program can use for $EXTMIN and $EXTMAX in the DXF file.

3.3. AddLayer(layer: String; color: Integer)

• Within the “layer table,” create a new layer with the given color index.

3.4. AddCircle(x, y, radius, color, layer)

• Writes the DXF statements for a circle entity at (x, y) with radius, assigned to some color and layer.

3.5. AddSubcatchPolyLine(aSubcatch, thickness, bulge, color, layer)

• Polylines the subcatchment’s polygon boundary. The code writes a “POLYLINE ... VERTEX ... SEQEND” block. The subcatchment’s polygon is accessed from aSubcatch.Vlist.

3.6. AddLinkPolyLine(aLink, thickness, bulge, color, layer)

• Similar to AddSubcatchPolyLine but for a link’s polyline (via aLink.Vlist plus the from/to node coords).

3.7. AddArrow(...)

• Renders the arrowhead for a link, by writing two line segments forming a “V” shape. The geometry is computed from start/end angles and arrow size.

3.8. AddText(x, y, ht, rot, txt, layer)

• Writes a text entity. Used for map labels.

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4. Data & Variables

1. Global/Module-level:

   • DXFfile: a TextFile handle for writing the DXF lines.
   • JuncStyle: integer controlling how junctions are drawn (0=circles, 1=cross, 2=filled squares).
   • SubcatchSize, LinkSize, NodeSize, LabelSize, ArrowSize: floating “scaling factors” from SWMM’s map to DXF.
   • PixPerMapExt: ratio to convert from map coordinates to screen or other dimension units, used for scaling.
   • DXFLinkColor, DXFNodeColor, DXFSubcatchColor: arrays for color indexes for different objects, matching SWMM’s color legend intervals.

2. Units: The code transforms local map units (from the SWMM map display) into raw DXF coordinates, effectively in the same coordinate system but scaled to represent line thickness, arrow sizes, etc.

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5. Flow of DXFexport

Below is a step-by-step outline of what DXFexport(...) does:

1. Open the output file at fname.
2. Initialize local variables with dimension and style settings from the SWMM map object.
3. Write:
   • AddHeader(...) with bounding box.
   • StartTables(...), AddLayer(...) calls, and EndTables.
4. Loop over subcatchments if they are shown; calls AddSubcatch(...) for each.
5. Loop over each link type (I in [CONDUIT, PUMP, ...]), calls AddLink(...).
6. Loop over each node type (I in [JUNCTION, OUTFALL, ...]), calls AddNode(...).
7. AddLabels if they are shown.
8. Close the DXF with EndDXF.
9. Close the file handle.

That’s how the entire map is rendered into lines, polylines, circles, etc.

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6. Practical Notes

• Colors: The code looks up the SWMM color (RGB) in DXFColors = (clRed, clYellow, ...), matching it to the “closest” index. This might be a limited approach but is standard for older DXF color indexes.
• Arrows: Only drawn if MapOptions.ArrowStyle is not asNone. The code calculates arrow geometry with SinCos(arctan2(...)) calls.
• Units: The SWMM coordinates are used directly, no special unit conversion is done. The user’s SWMM map coordinates are in some length unit that the DXF will interpret.
• File: The resulting .dxf is “AutoCAD Release 12 style” or older ASCII format, which is widely recognized.

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7. Conclusion

Udxf.pas provides a straightforward, if somewhat “low-level,” approach to generating a standard ASCII DXF file from an EPA SWMM map. It enumerates each item of interest (subcatchments, nodes, links, labels), converts them to the necessary DXF geometry calls (POLYLINE, CIRCLE, SOLID, TEXT), and organizes them into layers. This allows the SWMM map layout to be examined or edited in any CAD application supporting DXF.