GDD.LSP Open Source 3D Site Grading and Drainage Plan Designer Like Civil 3D Feature Lines for AutoCAD

This site is the source for the HawsEDC Free Software (see license below) tools, including this newly released in 2015 Site Grading and Drainage Plan Designer, a powerful 3D design tool like AutoCAD Civil 3D Feature Lines for site grading. I invite you to try out any of the tools here that interest you and to tell others if you find the tool valuable.

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Extract the zip file:
Uzip GDD and put all its files into a GDD folder that AutoCAD can write to. Generally, somewhere in your user (C:\Users\) folder is convenient. All the files should end up in the GDD folder without any subfolders.
Add GDD path to AutoCAD:
Under the Files tab of the Tools, Options menu in AutoCAD, click the + icon next to "Support File Search Path" and "Trusted Locations". Click the Add... button to add the GDD folder. You should be fine leaving it at the bottom of the list in most cases. Note to testers: if you don't want to add these paths, you can skip this step, open the gddtest.dwg drawing from the GDD folder and drag in the gdd.lsp file (or load it using your preferred method) after the next step.
Add GDD menu to AutoCAD:
Use the MENULOAD command in AutoCAD to load the GDD menu. Browse for the GDD.MNU file and Load it.


When you want to design the grading for a site without a calculator, you need a tool like AutoCAD Civil 3D Feature Lines or Grading and Drainage Designer so you can set the elevations of points based on other points, see the slopes between them, and make adjustments that are reflected in the appropriate slopes. Read more about Grading and Drainage Designer at the Wikia AutoCAD Wiki


If you are trying out GDD for the first time, open the gddtest.dwg drawing to get a feel for what GDD does. Note that GDD creates the following objects in your drawing.

Note next that GDD has a pull-down menu. Start by choosing "Insert Single Point" (IPS keyboard command) or "Insert Double Point" (IPD keyboard command). Follow the prompts to insert an elevation point. Note that you while gddtest.dwg is centered around elevation 1250, you should enter only 2 digit elevations because that is the convention for this project as shown by the points already present. GDD analyzes the drawing design to determine that the typical elevation of the gddtest.dwg drawing is about 1250 and the display elevations all drop the 1200.

Choose "Single Point by Slope" (IPSS command) or "Double Pointby Slope" (IPDS keyboard command) from the menu to insert a point at a reference slope from an existing point. If you don't want to choose a location for the slope arrow, choose "Prompt for connector placement" from the menu to uncheck it.

Use the menu to Raise/Lower or move one or more points or Edit Elevations.


If you can't see in your AutoCAD window the helpstrings that are provided to explain each GDD menu command, refer to the list below.

General Setup
Set up or change running program variables.
Set Avg Elev
Set Average Project Elevation.
Long Curve Segments
Set the curve error at 1.0
Short Curve Segments
Set the curve error at 0.001
Customize Curve Segments
Set the curve error per user input
Set 6" Curb
Set 6" Curb.
Set 4" Curb
Set 4" Curb.
Set Custom Curb
Set Custom Curb.
Insert &Single Point
IPS. Inserts a single point with user options.
Single Point By S&lope
Single Point By Slope. Inserts a single point by slope from another point.
Single Point By Elev Up/Down
Single Point by Distance. Inserts a single point by distance up from another point.
Insert Double Point IPD
IPD. Inserts a double point with user options.
Double Point By Slope
Double Point By Slope. Inserts a double point by slope from another point.
Double Point By Elev Up/Down
Double Point by Distance. Inserts a double point by distance up from another point.
Raise/Lower Point
Raise or Lower a Point by Specified Amount (- is down)
Relocate Point
Move a point horizontally to another location
Update Points and Connections
Update points to match display elevations and connections to match updated points.
Edit Elevationa by Slope
Edit the slope by selection
Insert Slope
Insert a Connection
Prompt for descriptions
Turn off or on the prompt for descriptions when inserting points.
Current automatic descriptions
Set the current descriptions to be used when inserting points.
Prompt for connection placement
Prompt for connection placement
Maximum manual prompts
Maximum # of connectors to prompt for manual placement in one operation.
Enable Z on Move Point
Toggle whether to move the Z coordinate of points when moving points


Date Programmer Revision
20151030 TGH 1.0.0 Published on web site.

To submit revisions, send an email with your revised code.


This program is free software under the terms of the GNU (GNU--acronym for Gnu's Not Unix--sounds like canoe) General Public License as published by the Free Software Foundation, version 2 of the License.

You can redistribute this software for any fee or no fee and/or modify it in any way, but it and ANY MODIFICATIONS OR DERIVATIONS continue to be governed by the license, which protects the perpetual availability of the software for free distribution and modification.

If you improve this software, make a revision submittal to the copyright owner. See

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License on the World Wide Web for more details.

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