DTM generation and bird eye view generation using a personal computer
The Bird Eye View Generation is to generate the projected image according to the selected vlew azimuth and vlew depression augle this procedure makes it possible to make an super imapose image between DTM data and recote scensing data. The bird-eye view generation technique which is used in the study is a three dimensional transformation and parallel projection including hidden surface elimination:
The DTM Generation is to generate the digital terrain model (DTM) from the digital elevation model (DEM). The function consists of:
- Slope Gradient (original data) is the steepness
of the terrain which varies from 0° to 90° from flat to steep. The
calculation function used to dtermine the gradient is
where
qd = slope gradleent of the terrain at the posltion of interest.
dzx = height dlifference in X direction.
dzy = height ddifference in Y direction.
dx = distance difference in X direction
dy = distance difference in y direction
- Slope Gradient (color rcpresentation) The output data is a level sliced image represented by colors (R.G.B)
- slope Aspect (original data) is the direction
of the normal vector of the tangent plane and it varies from 0° (north)
to 360° clockwlese. The value 400 is used for flat surfaces. The
calculation function used to determine the aspect is
Where
qa=slope aspect of the terrain at the position of interest.
dzx = height difference in X direction.
dzy = height difference in Y direction.
dx = distance difference in X direction.
dy = distance difference in Y direction.
- Slope Aspect (color representation):The output data is a level sliced image represented by colors (R,G,B).
- Relief Shading (original data) is to shade the surface according to the angle of the sun, the azimuth of the sun, the view angle, and the view azimuth. The output value varies from 0 to 100 from dark to bright. The calculation function which is used to shade the surface is
where
Sh = shading value.
Sx = the X component of the direction of ray of the sun
Sy = the Y component of the direction of a ray of the sun
Sx = Z component of the direction f ray of the sun
Tx = the X component of the normal vector of the tangent of the terrain.
Ty = the Y component of the normal vector of the tangent of the terrain.
Tz = the z component of the normal vector of the tangernt of the terain.
Ex = the X component of the view direction
Ey = the Y component of the view direction
Ez = the Z component of the view direction.
- Relief Shading (color representation): The output data is a level sliced image represented by colors (R.G.B)the Image Disply is to display te image on the screen using SUPER FRAME (image memory) which can display 256 gray levels in red. green, and blue.
The Image display is to display the image on the acteen using super frame (image memory) which can display 256 gray levels in red,green,and blue.
The utility functions consists of:
- Window Selection is to clip or select a part
from the image fle.
- Byte Conversion is to convert 1 byte data.
- Level Slicing is to rank the input data.
The Application functions consists fo:
- Contour lin e Interpolation is to generate a
contour map from the digital elevation model (DEM)
- Pfofile Analysis is to analyze teshape of the
terrain as for profile and cross section from the digital elevation
model (DEM)
- Stereo View Generation is to generate stereo
pair images.
Conclusion
In this paper, we have presented the implementation of a software package for DTM generation and bird eye view generation . The development of the software is ongoing task. At present. it is implemented on a NEC -9801 RA 5 in a NEC-DOS environment. We intend to verify the utility and application functions for to be applicable to ve\arious fields of work.
Reference:
- William MNcwamam Robert F. Sproull,Principles of Interactss Computer Graplic MC. Graw Hill International Book Company.
