3D Topography

[Conrad Hoffman]

I have a very low resolution "map" of a surface- 5 x 50 points or so. I want to display this as a tilted 3D topography map but I'm a bit confused as to the best method. Is it best dealt with as an image or a graph? I can write some simple display code, but don't want to reinvent the wheel, nor do I know how to do surfaces and lighting. Not sure how to make such a low res thing look good- if I had more points it would actually be easier. I don't want to buy an expensive package for this one time thing. Can anybody point me to some suitable PBWin code or give me an example of what I need to write? Thx!

[Petr Schreiber jr]

I would recommend to study a bit samples on José Roca's forum.
For this task you can use:

OpenGL

Direct3D

I personally prefer OpenGL, it is quite easy to jump in, and it still provides interface for everything you need to get from 3D card.
On José's web you can find "raw SDK" OpenGL samples as well as some using higher level libraries. All with tutorials going from single triangle render to more complex topics - so lot of code for study.

You can render the terrain using immediate mode ( glBegin / glVertex3f / glEnd ) first and then you can start to optimize using vertex arrays/vertex buffers/display lists once you get the idea.


Petr

[Conrad Hoffman]

Petr- Thanks, looked at the first Opengl demo and it's exactly what I need to do. Hopefully my pea sized brain can figure this out in a reasonable time. I know 12 year old game programmers can do this blindfolded, but there's never a 12 year old around when you need one.

[Petr Schreiber jr]

Try to use some of the most basic José's OpenGL skeletons, and for rendering use following:

sub Array2Surface( byref Arr() as single )
  register i as long, j as long
  local s1, s2 as long
  local mini, maxi, delta as single
  s1 = ubound(Arr,1)
  s2 = ubound(Arr,2)

  mini = 1000000000
  maxi =-1000000000
  
  ' -- Get min max values, useful for colors
  for i = 1 to s1
    for j = 1 to s2
      mini = min(mini, MyArray(i,j))
      maxi = max(maxi, MyArray(i,j))
    next
  next    
  
  delta = maxi - mini
  
  glPushMatrix
    ' -- Center the final mesh
    glTranslatef -s1/2,0,-s2/2    
    
    ' -- Green color
    glColor3ub 0, 255, 0
    
    ' -- Mesh building - via the most dummy way, but works :)
    glBegin %GL_TRIANGLES
      for i = 1 to s1-1
                 
        for j = 1 to s2-1
          
          glColor3ub 0, (MyArray(i,j)-mini) / delta * 255, 0
          glVertex3f i, MyArray(i,j),j
          
          glColor3ub 0, (MyArray(i+1,j)-mini) / delta * 255, 0          
          glVertex3f i+1, MyArray(i+1,j),j        
          
          glColor3ub 0, (MyArray(i+1,j+1)-mini) / delta * 255, 0          
          glVertex3f i+1, MyArray(i+1,j+1),j+1          
                   
          glColor3ub 0, (MyArray(i,j+1)-mini) / delta * 255, 0
          glVertex3f i, MyArray(i,j+1),j+1        
                    
          glColor3ub 0, (MyArray(i,j)-mini) / delta * 255, 0
          glVertex3f i, MyArray(i,j),j
                    
          glColor3ub 0, (MyArray(i+1,j+1)-mini) / delta * 255, 0          
          glVertex3f i+1, MyArray(i+1,j+1),j+1        

        next  
      next             
      
    glEnd        
  glPopMatrix
  
end sub

So if you have 5x50 array, you could try something like:

glClear %GL_COLOR_BUFFER_BIT OR %GL_DEPTH_BUFFER_BIT
glLoadIdentity   

gluLookAt ( 50, 50, 50, 0, 0, 0, 0, 1, 0 )

Array2Surface(MyArray())

wglSwapBuffers(hDc)

( MyArray should be 2D array )

It should render the terrain with lowest points in black and higher the vertex is, more green it gains.


Bye,
Petr

[Conrad Hoffman]

Hi Petr,
That's much easier- thanks! I'll be working on this over the next couple weeks.

CH

[dean goodman]

Before you go to Open GL, you will need to regrid your data to higher density using interpolation software. 5X50 is very coarse topo data. Inverse distance would work fine enough... and of course there are more sophisticated interpolation schemes such as Krigging, minimum curvature...etc...