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Introduction to SimTaDyn

SimTaDyn: a dynamical spreadsheet for geographic simulation (SIMulateur TAbleur DYNamique in french).

The following figure is a screenshot of the legacy version of SimTaDyn. alt tag

State of Art

SimTaDyn is a proof of concept for a geographic information system (GIS) allowing to draw geographic maps, to edit their information and formulas like done in a spreadsheet editor, and finally, execute the map dynamically like dynamical systems.

A spreadsheet, like Excel, edits pages of regular and rectangular pavement. Cells (aka tile) contain either a literal value or a formula which performs an action on the cell itself with the content of other cells.

A Geographic Information System (GIS) is an editor manipulating geographic databases and draw their information. Datum are usually not dynamic (in the way modifying one set over time will dynamically change other datum).

The idea of SimTaDyn is to couple in a single tool a GIS with a spreadsheet but the goal is to extend their ideas to a more general case:

  1. The idea of spreadsheet is extended: In SimTaDyn the pavement is more general and contains different kind of editable tiles (cells):

  • Polygonal cells (like a geographic area) extend the regular and rectangular pavement of classic Excel spreadsheets.

  • Edge cells (like roads or points of interest) extend the pavement of classic spreadsheets by allowing edges to be interactive as well polygonal cells (which is not the case on Excel).

  • Node cells (like road crossings) extend the pavement of classic spreadsheets by allowing corners to be interactive (which is not the case on Excel).

This idea is summarized by the following picture:

alt tag

  1. The idea of spreadsheet scripting is extended: Like classic spreadsheets, SimTaDyn has a script language for "gluing" cells together by formulas. SimTaDyn extends with self-evolving scripting language: the Forth language instead of a static language like Visual Basic.

Forth is a stack language (reverse polish notation), embedding its own virtual machine (managing it's own memory, dictionary, byte code) and its own interpreter (compiler). Forth is very powerful because because it's a self-evolving language: the interpreter evolves dynamically and can modify its own syntax.

  1. The idea of spreadsheet scripting is extended: A classic spreadsheet only manages one literal value or a formulae. SimTaDyn wants to work on a database: each cell can have more than one data and at most one forth script as formulae. And thanks to Forth you can write complex formulas like discrete time systems.

  2. The idea of spreadsheet scripting is extended: The Forth editor of SimTaDyn allows to write and run two kind of scripts:

  • Local scripts are stored inside cells like a classic spreadsheet.

  • Global scripts are applied to the whole map (launching Forth script on all cells), modifying its layout or information, ...

  1. The idea of GIS is also extended: classic GIS manipulates two kind of geographic maps.

SimTaDyn can be seen as a vectorized map manipulated like a rasterized map. Each cell is a either a polygon, a polyline or dots but are at the same time a cell with a script forth and an data from the database.

  1. The idea of GIS is also extended: Because SimTaDyn uses OpenGL and Forth has an evolving scripting language, we can display results of a script in 3D instead of 2D.

Typical SimTaDyn applications

Application with this SimTaDyn is not limited to GIS application, we can imagine using SimTaDyn for the following applications:

  • A pure classic spreadsheet, Excel-like, where nodes and arcs have no effects, zones are rectangular.

  • A game engine for making a clone of the SimCity game. Or more seriously for resolving problem of traffic jam/congestion and Wardrop's equilibrium.

  • Solving partial differential equation like the video showing SpaceX simulations.

  • A flowchart in the same idea of Lego Mindstorms: nodes are Forth code and edges the order sequences. Or blocks schematics for flow control like Simulink or Scicos.

As said previously, SimTaDyn is still a proof of concept and is still looking for its way and GIS is one of the possible way.

Origin of the project

SimTaDyn was at this origin a one-year free-subject school project made in 2003-2004 at EPITA school for learning coding and working in team. The project reborn in 2017, after a talk with a co-worker and I decided to give this project a second life. The original code was so messy that I decide to develop it again but "from scratch" and in C++ with cleaner code (I hope).

The SimTaDyn name comes from a joke mixing words SIM (for SimCity, SIMulation), TA (for TABleur: spreadsheet in French), DYN (for DYNamic) and sounding close to the project Sytadin a traffic jam application where the name is also a joke to the French word citadine (meaning city-dweller).

For frenchmen, you can read the french PDF manual written in 2004 as support for our teachers (badly written due to a miss of time).

The initial code is available on the git branch release-EPITA-2004 branch. The project was not fully finalized but functional. To compile it, you will need to install libraries like MySQL, OpenGL (the legacy version), GTK+2, gtkglext (OpenGL for GTK+2), ncurses and worked for OSX with X11 and still working on actual Linux (but no longer on recent OSX versions because GTK+/Opengl is no longer maintained).