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Rendering Shapefile in OpenGL

By , 29 Dec 2008
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Introduction

ESRI shapefiles are well known vector data formats used for Mapping a.k.a GIS applications. There are many open source softwares like JUMP, SharpMap that allow the users to view the shapefiles. This article focuses on rendering them in OpenGL console.

Background

Shapefiles hold geographic information in the form of points, lines and polygons. For instance- political boundaries like Countries, States are treated as Polygon shapefiles; linear features such as roads, rivers are Line shapefiles and; Airports or BusBays are sometimes treated as point shapefiles.

Using the Code

I assume that the intended audience is familiar with OpenGL and understands concepts like linking with static or dynamic libraries in Microsoft Visual Studio environment.

To parse the shapefile, I have used the Shapelib (http://shapelib.maptools.org/). Include the shapefile.h at the beginning. Make use of the shapelib.lib by adding shapelib\shapelib.lib to object/library Modules by going to Project>Settings>Link.

   #include "shapelib\shapefil.h"

Call the following function to Open Shapefile by passing the .shp file name. The function parses the geographic coordinate information and stores them in the Vectors vPoints, vLines and vPolygons.

  //Function to Open Shapefile and parse the info 
  void OpenShapeFile(char* fileName)

SBoundingBox is a structure defined to hold the bounding box of the shapefile. Bounding box coordinates are read in OpenShapeFile function and assigned as glOrtho() parameters, which would restrict the limits of display to the rectangle enveloping the area of interest.

 //Assign Bounding Box Coordinates of Shapefile to glOrtho()
 glOrtho(sBoundingBox.fMinX, sBoundingBox.fMaxX,
	sBoundingBox.fMinY,sBoundingBox.fMaxY,-1,1);

Finally, it is just a matter of setting appropriate OpenGL primitives(GL_POINTS, GL_LINE_STRIP, GL_LINE_LOOP) to render Point, Line or Polygon type shapefile.

void draw()
{
  //Render Point Shapefile glColor3f (0.0, 0.0, 1.0);
   glEnable(GL_POINT_SMOOTH) ; 
   glPointSize(5.0); 
   glBegin(GL_POINTS); 
   for(int i=0;i < vPoints.size();i++)  
   {
    glVertex2f(vPoints[i].dX,vPoints[i].dY); 
    glEnd();
   } 
   	
	//Render Line Shapefile
	glColor3f (0.0, 1.0, 0.0);
	for( i=0;i < vLines.size();i++)
	{
		glBegin(GL_LINE_STRIP);
		for(int j=0;< vLines[i].vPointList.size();j++)
		{
		  glVertex2f(vLines[i].vPointList[j].dX,vLines[i].vPointList[j].dY);
		}
		glEnd();
	}
	
	//Render Polygon Shapefile
	glColor3f(1.0,0.0, 0.0);
	for( i=0;i < vPolygons.size();i++)
	{
		glBegin(GL_LINE_LOOP);
		for(int j=0;j <vPolygons[i].vPointList.size();j++)
		{
			glVertex2f(vPolygons[i].vPointList[j].dX,
					vPolygons[i].vPointList[j].dY);
		}
		glEnd();
	}
    glFlush();  
}

Output

Sample Output- OpenGL Console

Points of Interest

It would be nice if someone comes up with ways to read/apply/reproject the .shp file by reading the projection information from .prj files accompanied with .shp files. PROJ.4 is an Open Source projection library if you want to give it a try.

Experimenting with pan and zoom features will be a good challenge.

Maintaining Aspect Ratio is a predominant feature in GIS applications. I leave it to you as another feature to explore.

History

  • 29th December, 2008: Initial post

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Durga Prasad Dhulipudi
Software Developer
India India
He works in the GIS and allied technologies. His areas of Interest are GIS/CAD ,Defence,Aerospace and Law Enforcement.

Comments and Discussions

 
QuestionAre you sure the OpenShapeFile function parses the geographic coordinate information and stores them Pinmembersepinaz15-Sep-13 2:17 
QuestionHow to use projrction of the layer in order to have a better view in OpenGL Pinmembersepinaz14-Sep-13 20:02 
QuestionGDI? PinmemberNite12-Mar-10 17:54 
AnswerRe: GDI? PinmemberDurga Prasad Dhulipudi25-Mar-10 18:26 
Let me try doing it in GDI.I guess the challenge would be to divide the screen coordinates into map coordinates.Let me know whether you are looking for solution in GDI or GDI+ or WPF.
Don't be ruffled if now and then you get a brush from the world; it will be over in no time, and everything will be all right.(Swami Vivekananda)

GeneralRe: GDI? PinmemberNite26-Mar-10 3:25 
GeneralRe: GDI? PinmemberDurga Prasad Dhulipudi8-Apr-10 23:04 
Generalno shaders :( PinmemberAdrian Pasik2-Nov-09 7:42 
GeneralUse Shapelib On Mac OS X Pinmemberandyce856-Aug-09 11:11 
GeneralRe: Use Shapelib On Mac OS X PinmemberCatalin Curta27-Nov-12 21:59 
QuestionHow to use this code in c++ builder? Pinmemberjosephspeak20-Jul-09 22:14 
QuestionHow Draw polygon with holes PinmemberMember 155633111-Mar-09 16:17 
AnswerRe: How Draw polygon with holes PinmemberDurga Prasad Dhulipudi8-Apr-09 18:08 
Generalwhat's the benifite PinmemberMartial Spirit6-Jan-09 1:05 
GeneralRe: what's the benifite PinmemberDurga Prasad Dhulipudi8-Jan-09 0:21 
GeneralNeeds glut32.dll Pinmembergxdata5-Jan-09 13:19 

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