Multi-layer atmospheric fading in real-time computer image generator

• US 5,357,579 A
• Filed: 07/15/1993
• Issued: 10/18/1994
• Est. Priority Date: 09/03/1991
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Martin Marietta Corporation
• Inventors: Kelly, William A., Buchner, Gregory C.
• Primary Examiner(s): Boudreau, Leo H.
• Application Number:
  US08/091,380
• Time in Patent Office: 460 Days
• Field of Search: 382/1, 395/118, 395/126, 395/127, 395/119, 345/9, 345/27, 345/112, 345/117, 434/36, 434/38, 434/41, 434/43, 434/44
• US Class Current: 382/100
• CPC Class Codes: G06T 15/50 Lighting effects

Abstract

The effect of multi-layer atmospheric scattering on the visibility F of each point P on a visible surface of each polygon in a display scene, in a computer image generation (CIG) system, is provided by determining the effective average reciprocal half-fading distance between viewpoint and the viewed point, knowing the altitudes at which each of the different scattering layers start and accounting for any transitional slopes therebetween. The total reduced visibility of that viewed point P is a function of the average reciprocal half-fading distance for that point and of the total range between the viewed point P and the viewpoint VP.

Claims

1. A method for modifying the color (chromicity and intensity) of light to be emitted at each pixel of a display scene in a computer image generation (CIG) system, responsive to a fading effect of scattering through a plurality n of different atmospheric layers on the visibility F_p from a viewpoint VP of each separate one of a multiplicity of viewed points P on each visible polygon surface in that scene, comprising the steps of:

(a) providing (1) a signal containing at least altitude Alt_VP data for the viewpoint VP for the present scene to be displayed, (2) a separate data signal representing a location of each of the plurality of viewed points P of the present scene, and (3) a set of other data signals, each representing a beginning altitude Alt L_i, for 1≦

i≦

n, for the i-th one of the plurality n of scattering layers;

(b) providing an associated different one of a multiplicity of input data signals C_p for the color of each separate point P in the present scene;

(c) separately generating, for each point P of the scene, an inverse range data signal, responsive to a viewscreen data signal, obtained from the VP and P data signals, of a viewscreen location (I_p,J_p) of a viewray from the viewpoint VP to that viewed point P;

(d) generating another data signal representing an altitude Alt_p of the viewed point P;

(e) generating, from the Alt_p and Alt_VP data signals and the set of Alt L_i data signals, an effective cumulative layer half-fading reciprocal distance (1/Df_eff.sbsb.--_cumm) data signal;

(f) generating a data signal representing a total diminished visibility F_p of point P from viewpoint VP through all of the intervening scattering layers, responsive to selected ones of the inverse range, viewed point altitude, viewpoint altitude and effective cumulative layer half-fading reciprocal distance data signals; and

(g) modifying the received data signals C_p, responsive to the point P diminished visibility data signal F_p, to an output data signal C_f used to determine the color and intensity of the visible light emitted by at least one display pixel associated with each viewed point P of the scene then being displayed.

2. The method of claim 1, wherein step (f) includes the steps of:

generating a data signal for an effective half-fading reciprocal distance (1/Df_eff) from the Alt_p, Alt_VP and (1/Df_eff.sbsb.--_cumm) data signals;

generating (R/Df) data signals as a function of the inverse range and (1/Df_eff) data signals; and

generating the diminished visibility function F_p data signal by processing of the resulting (R/Df) data signals.

3. The method of claim 2, wherein step (f) further includes the steps of:

generating a data signal from an absolute difference in the Alt_VP and Alt_P data signals; and

generating the (1/Df_eff) data signals as a function of the (1/Df_eff.sbsb.--_cumm) data signals and the absolute altitude difference data signals.

4. The method of claim 1, wherein step (c) includes the step of generating the inverse range data signal as a preselected function f1=(C₄ +C₅ I_p +C₆ J_p), where C₄, C₅ and C₆ are predetermined constants of the viewscreen data signal for that point.

5. The method of claim 4, wherein step (d) includes the steps of:

generating a data signal for another preselected function f2=(C₁ +C₂ I_p +C₃ J_p), where C₁, C₂ and C₃ are other predetermined constants, of the viewscreen data signal; and

generating the Alt_p data signal as a quotient of the f1 and f2 data signals.

6. The method of claim 1, wherein step (e) includes the steps of:

determining, for each layer L between the altitude Alt_p of point P and the altitude Alt_VP of viewpoint VP, a data signal responsive to a difference in altitude of that layer L from the point P and at least one layer half-fading distance characteristic; and

then generating the (1/Df_eff.sbsb.--_cumm) data signals from the determined layer altitude difference data signals.

7. The method of claim 6, wherein the difference-determining step includes the steps of:

comparing the present viewpoint altitude Alt_VP to the lower altitude Alt L_i of each associated layer; and

providing a data signal, responsive to the comparisons, indicating the highest layer in which the viewpoint is contained.

8. The method of claim 7, wherein the difference-determining step further includes the step of providing Alt L_i signal data by selecting an altitude data signal for the lower altitude of the highest-contained layer.

9. The method of claim 8, wherein step (c) also includes the step of storing signal data for at least one intermediate layer for each layer lying between the highest-contained layer and the layer containing the point P.

10. The method of claim 6, wherein the then-generating step includes the step of generating the total effective fading data signal responsive to a function (1/Df_eff.sbsb.--_cumm.sbsb.--_p)=(1/Df_cumm.sbsb.--_l)+(Alt_p -Alt_l)*(1/Df_l)+S*(Alt_p -Alt_l)² *(1/2)(1/Df_m), where S=0 if the viewpoint is not in a transitional-density layer and S=1 if the viewpoint is in a transitional-density layer.

11. Apparatus for modifying the color (chromicity and intensity) of light to be emitted at each pixel of a display scene in a computer image generation (CIG) system, responsive to a fading effect of scattering through a plurality n of different atmospheric layers on the visibility F_p from a viewpoint VP of each separate one of a multiplicity of viewed points P on each visible polygon surface in that scene, comprising:

first means for receiving (1) a signal containing at least altitude Alt_VP data for the viewpoint VP for the present scene to be displayed, (2) a separate data signal representing a location of each of the plurality of viewed points P of the present scene, and (3) a set of other data signals, each representing a beginning altitude Alt L_i, for 1≦

i≦

n, for each i-th one of the plurality n of scattering layers;

second means for receiving an associated different one of a multiplicity of input data signal C_p for the color of each separate point P in the present scene;

third means for separately generating, for each point P of the scene, an inverse range data signal, responsive to a viewscreen data signal, obtained from the VP and P data signals, of a viewscreen location (I_p,J_p) of a viewray from the viewpoint VP to that viewed point P;

fourth means for generating another data signal representing an altitude Alt_p of the viewed point P;

fifth means for generating, from the Alt_p and Alt_VP data signals and the set of Alt L_i data signals, an effective cumulative layer half-fading reciprocal distance (1/Df_eff.sbsb.--_cumm) data signal;

sixth means for generating a data signal representing a total diminished visibility F_p of point P from viewpoint VP through all of the intervening scattering layers, responsive to selected ones of the inverse range, viewed point altitude, viewpoint altitude and effective cumulative layer half-fading reciprocal distance data signals; and

seventh means for modifying the second means data signals C_p, responsive to the point P diminished visibility data signal F_p from the sixth means, to an output data signal C_f used to determine the color and intensity of the visible light emitted by at least one display pixel associated with each viewed point P of the scene then being displayed.

12. The apparatus of claim 11, wherein the sixth means includes:

ninth means, responsive to the Alt_p, Alt_VP and (1/Df_eff.sbsb.--_cumm) data signals, for generating an effective half-fading reciprocal distance (1/Df_eff) data signal;

means for generating (R/Df) data signals as a function of the inverse range and (1/Df_eff) data signals; and

means for generating the diminished visibility function F_p data signal responsive to the resulting (R/Df) data signal.

13. The apparatus of claim 12, wherein said ninth means includes:

means for generating a data signal responsive to an absolute difference in the Alt_VP and Alt_p data signals; and

means for generating the (1/Df_eff) data signal as a function of the (1/Df_eff.sbsb.--_cumm) data signal and the absolute altitude difference data signal.

14. The apparatus of claim 11, wherein said third means includes means for generating the inverse range data signal as a preselected function f1=(C₄ +C₅ I_p +C₆ J_p), where C₄, C₅ and C₆ are predetermined constants, of the viewscreen data signals for that point.

15. The apparatus of claim 14, wherein said fourth means includes:

means for generating another preselected function f2=(C₁ +C₂ I_p +C₃ J_p) data signal, where C₁, C₂ and C₃ are other predetermined constants, from the viewscreen data signals for that point; and

means for generating the Alt_p data signal as a quotient of the f1 and f2 data signals.

16. The apparatus of claim 11, wherein said fifth means includes:

means for determining, for each layer L between the altitude Alt_p of point P and the altitude Alt_VP of viewpoint VP, a data signal responsive to a difference in altitude of that layer L from the point P and at least one layer half-fading distance characteristic; and

means for then generating the (1/Df_eff.sbsb.--_cumm) data signals from the determined layer altitude difference data signals.

17. The apparatus of claim 16, wherein the difference-determining means includes:

a plurality n of means each for comparing the present viewpoint altitude Alt_VP to the lower altitude Alt L_i of each associated layer; and

means, responsive to the plurality of comparing means, for indicating the highest layer in which the viewpoint is contained.

18. The apparatus of claim 17, wherein the difference-determining means further includes means for providing Alt L_i signal data by selecting an altitude data signal for the lower altitude of the highest-contained layer.

19. The apparatus of claim 18, wherein said fifth means also includes a memory for storing signal data for at least one intermediate layer for each layer lying between the highest-contained layer and the layer containing the point P.

20. The apparatus of claim 16, wherein said then-generating means includes means for generating the total effective fading data signal responsive to a function (1/Df_eff.sbsb.--_cumm.sbsb.--_p)=(1/Df_cumm.sbsb.--_l)+(Alt_p -Alt_l)*(1/Df_l)+S*(Alt_p -Alt_l)² *(1/2)(1Df_m), where S=0 if the viewpoint is not in a transitional-density layer and S=1 if the viewpoint is in a transitional-density layer.