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DTM generation and bird eye view generation using a personal computer

Suits Visehsin(Talland),Shunji Murai (Japan)
Institute of Industrial Science. University of Tokyo
7-22, Roppongi, Minato-ku, Tokyo 106


Abstract
Software for digital terrain model (DTM) generation and bird-eye view enervation using a personal computer has been developed. The software is divided into two parts. One is the DTM generation to generate slope aspect. Slope gradient and relief shading of the terrain. The other is the bird-eye view generation to generate a bridge view image of the te5rain from any view direction and any depression angle. The bid eye view generation can also be used to produce a superimpose image between DTM data and other satellite data.

Introduction
Recently, demand on digitized map information of high precision and regular grid digital terrain model (DTMS) have become larger and larger in various fields. Since computers come to play an important role in photogrammetry and remote sensing, many procedures can now be processed faster than before.

Within the last few years, microelectronics, especially personal computer technology, has made a remarkable progress. The DTM generation and bird-eye view generation, which earlier were possible only with expensive large sale computer system, have become somewhat feasible with personal computers.

The objective of this study is to utilize the advantage of personal computers to develop a cheap system for generating DTM and bird-eye view image data.

Personal Computer Hardware Configuration
Fig. 1 shows the hardware configuration of the personal computer used for this system. The computer is a NEC PC 9801 RA5. The computer system consists of 32-bit microprocessor as CPU. Mathematical coprocessor. 640 KB main memory, 256 KB graphic memory, 20 MB or 40 MB hard disk drive, dual 5" floppy disk drives, analog color display, mouse and a keyboard. An optional image memory card (SUPER FRAME) is used for display of the image data.

This software can actually work on any 16-bit NEC computer (ie. NEC Pc -9801 Vm/Vx) but the processing time will then increase.


Fig. 1 Hardware conflguration of the system

Software Functions
The software has been named DTMAN (Analysis). Fig. 2 shows the functions which are available.


Fig.2 Outline of the software

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:
  1. 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

  2. Slope Gradient (color rcpresentation) The output data is a level sliced image represented by colors (R.G.B)

  3. 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.

  4. Slope Aspect (color representation):The output data is a level sliced image represented by colors (R,G,B).

  5. 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.

  6. 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:
  1. Window Selection is to clip or select a part from the image fle.

  2. Byte Conversion is to convert 1 byte data.

  3. Level Slicing is to rank the input data.

The Application functions consists fo:
  1. Contour lin e Interpolation is to generate a contour map from the digital elevation model (DEM)

  2. Pfofile Analysis is to analyze teshape of the terrain as for profile and cross section from the digital elevation model (DEM)

  3. 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.