International Archives of the Photogrammetry. Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
The road elements sign are defined as follow:
[00 stands for road center point, 99-100 and 98-100 stand for
road center greenbelt, 1-99 and 2-98 stand for left and right road
surfaces respectively, 5-1 and 6-2 stand for left and right
roadbed respectively, 17-11 and 16-10 stand for left and right
road ditch respectively, 7-19 and 8-18 stand for left and right
road counterfort respectively.
The transect-based road model has a powerful potential, the
roadbed, road ditch, road counterfort are all expressed in the
transect. The road transect can change if there is no road ditch
or no counterfort in the course of road design. The road will be
finished as long as the road center line and the road transects are
set.
2.4 The Modelling of the Road with the Transect-based
Model
2.4.1 The Road Center Line Data and the Azimuth Angle
The road center line is a very important character of a road.
Once the road center line is set, the road line form is determined.
In general, the road center line is defined as stake: KAZB (A
and B stand for the distance ) The azimuth is define as the
horizontal angle of the road transect's bearing in surveying,
measured clockwise from a referent direction as from the north.
Road stake structure is defined as follow:
typedef struct {
float stake;
the beginning
POINT3D pt;
double angle;
lies in this stake
Stake;
Road center line is composited by many stakes, and it is defined
as follow:
CArray< Stake, Stake >RoadCenterLineArray
center line
/Ahe distance of road center point to
/Ahe center point, including x. y, z
/Ahe azimuth angle of transect which
//the road
2.4.2 The Road Transect Data and Structure
In general, the road transect character points such as | in the
transect are defined as the number sign, the distance from this
point to the road center point 100, and the height. The road
transect character points are defined as follow:
typedef struct tagTranPoint {
int id; /Ahe road transect character point
number sign
double dist;
road center point 100
doubel height;
| TranPoint;
The road transect is composited by the stake number, and
the transect character point array, which is defined as follow:
typedef struct tagRoadTransect {
float stake; /the transect stake
CArray< TranPoint, TranPoint >TranPointArray; //the
road transect character point array
) RoadTransect.
/fthe distance from this point to the
/Ahe height
2.4.3 The Modelling of Road
The transect-based road model is applied to the modelling of
road, the road designer can plan the road line form according to
the terrain, the road land use, and the road line style. The road
stake can choose 20 meter distance where the road transect
change less, otherwise the stake distance can bc shorten, and the
road transects arc added.
The same ID character point on border upon transects are linked,
and make the triangle partition ( Figure 5 ). If there is the ID
character point on the one of the transects, and there is not the
same ID character point on the other transect, this ID character
point will be linked to the less distance character point on the
other transect.
100
Transect 1
Transect 2
Figure 5. A Simplest Road Made up of Two Transects
3. THE VISUALIZATION OF THE ROAD
OpenGL is applied as the visualization tool of the road.
OpenGL is a software interface to graphics hardware. This
interface consists of about 120 distinct commands, which you
use to specify the objects and operations needed to produce
interactive three-dimensional applications. OpenGL is designed
to work efficiently even if the computer that displays the
graphics you create isn't the computer that runs your graphics
program. OpenGL is designed as a streamlined, hardware-
independent interface to be implemented on many different
hardware platforms. To achieve these qualities, no commands
for performing windowing tasks or obtaining user input are
included in OpenGL, instead, you must work through whatever
windows system controls the particular hardware you're using.
Similarly, OpenGL doesn't provide high-level commands for
describing models of three-dimensional objects. Such
commands might allow you to specify relatively complicated
shapes such as automobiles, parts of the body, airplanes, or
molecules. With OpenGL, you must build up your desired
model from a small set of geometric primitive-points, lines, and
polygons.
The visualization of the road is that the modelling of the road
elements are visualized with OpenGL. The map texture
technology can improve the simulation vision, the different road
elements will be mapped different texture. Level of Detail
( LOD ) algorithm can improve the speed of the road roam, and
effective visualization.
4. THREE-DIMENSIONAL ROAD SYSTEM, VIRTUAL
ROAD ( VROAD)
Based on the study of the transeet-based road model. a three-
dimensional road system called Virtual Road ( VRoad ) has
been developed by using VC” 6.0 and OpenGL. VRoad mainly
includes two parties: two-dimensional road map and three-
dimensional road scene. It includes four function module, which
are data import/output module, road modelling module, 2D map
module, 3D road landscape roam module. VRoad can fulfil an
interactive response in the 2D road map and the 3D road scene,
when roaming run to a place in the road 3D scene, the navigator
will display the place in the 2D map, which is an integration
that the 2D map's through virtue and the 3D scene's party virtue
(figure 6).
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