Road plan
---------
* Use Vertex Arrays/
  VertexBufferObjects/
  DisplayLists/
  glInterleavedArrays
* States/cities/roads overlays

Roam update
-----------

  x # Gis:
  x gis_update_tiles(tiles);
  x   for (tile in tiles)
  x     if (need_split(tiles))
  x       tiles << split(tile)
  x gis_render_surface(Image *img)
  x   polys = roam_get_intersecting_polies(img)
  x   for (poly in plies)
  x     render(img, poly)

    # Roam:
    on_view_change:
      roam_update_errors(roam)
    on_timeout:
      split_merge:
        if (height_func())
           vertex_heght = roam->height_func()
        else
           vertex_heght = 0

  x # GisPluginSrtm:
  x on_view_change:
  x   roam->height_func = srtm_height_func
  x   gis_update_tiles(tiles)
  x   for (new_tiles in tiles)
  x     points = roam_get_intersecting_points(tile)
  x     for (poly in plies)
  x       render(img, poly)

  x # GisPluginBmng:
  x on_view_change:
  x   gis_update_tiles(tiles)
  x on_render:
  x   for tile in tiles:
  x     gis_render_surface(gis, tile)