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

Claim 2

The method of claim 1, wherein step (d) includes the steps of: finding data for an effective half-fading reciprocal distance (1/Df eff ) from the Alt P data, the Alt VP data and the (1/Df eff_cumm ) data; finding (R/Df) data as a function of the inverse range data and the (1/Df eff ) data; and for finding the diminished visibility function F P from the resulting (R/Df) data.

Claim 3

The method of claim 2, wherein step (d) further includes the steps of: finding the absolute difference in the altitudes of the viewing and viewed points; and finding the (1/Df eff ) data as a function of the (1/Df eff_cumm ) data and the absolute altitude difference data.

Claim 4

The method of claim 1, wherein step (a) includes the step of generating the inverse range data as a preselected function f1 = (C₄ + C₅I p + C₆J p ), where C₄, C₅ and C₆ are predetermined constants.

Claim 5

The method of claim 4, wherein step (b) includes the steps of: generating data for another preselected function f2 = (C₁ + C₂I p + C₃J p ), where C₁, C₂ and C₃ are other predetermined constants; and finding the Alt p data as a quotient of f1 and f2

Claim 6

The method of claim 1, wherein step (c) includes the steps of: finding, for each layer L between the altitude of point P and the viewpoint VP, the difference in altitude of that layer L from the point P and at least one layer half-fading distance characteristic; and determining the (1/Df eff_cumm ) data from the found layer data.

Claim 7

The method of claim 6, wherein the difference-finding step includes the steps of: comparing the present viewing point altitude to the lower altitude of each associated layer; and providing data, responsive to the comparisons, indicating the highest layer in which the view point is contained.

Claim 8

The method of claim 7, wherein the difference-finding step further includes the step of providing Alt L data by selecting altitude data for the lower altitude of the highest contained layer.

Claim 9

The method of claim 8, wherein step (c) also includes the step of storing at least one intermediate layer quantity data for each layer capable of being addressed by the encoded data.

Claim 10

The method of claim 6, wherein the layer-data-using step includes the step of finding the value of a function (1/Df eff_cumm ) = (1/Df cumm_1 ) + (Alt P -Alt₁)*(1/Df₁) + S * (Alt p -Alt₁)² * (1/2)(1/Df m ), where S = 0 if the viewing point is not in a transitional-density layer and S = 1 if the viewing point is in a transitional-density layer.

Claim 11

Apparatus for determining the fading effect of scattering through a plurality n of different atmospheric layers on the visibility F p from a viewing point VP of each viewed point P on a visible surface of each polygon in a display scene in a computer image generation (CIG) system, comprising: first means for determining an inverse range, responsive to a viewscreen location (I p ,J p ) of a viewray from viewing point VP to viewed point P; second means for determining an altitude Alt P of the viewed point P; third means, responsive to the viewed point altitude and to an altitude Alt VP of the viewing point VP and to an altitude Alt L i , for 1≦i≦n, at which each i-th one of the scattering layers begins, for determining an effective cumulative layer half-fading reciprocal distance (1/Df eff_cumm ); and fourth means for determining the total diminished visibility F p of point P from viewing point VP through all of the intervening scattering layers, responsive to selected ones of the inverse range, viewed point altitude, viewing point altitude and effective cumulative layer half-fading reciprocal distance data.

Claim 12

The apparatus of claim 11, wherein the fourth means includes: fifth means for finding data for an effective half-fading reciprocal distance ( 1/Df eff ) from the Alt p data, the Alt VP data and the (1/Df eff_cumm ) data; a divider means for finding (R/Df) data from a quotient of the inverse range data and the (1/Df eff ) data and an exponentiator means for finding the diminished visibility function F p from the resulting (R/Df) data.

Claim 13

The apparatus of claim 12, wherein the fifth means includes: sixth means for finding the absolute difference in the altitudes of the viewing and viewed points; and means for finding said (1/Df eff ) data as a quotient of the (1/Df eff_cumm ) output data of the third means and the output data of the sixth means.

Claim 14

The apparatus of claim 11, wherein said first means is a function generator for generating the inverse range data as a preselected function f1 = (C₄ + C₅I p + C₆J p ), where C₄, C₅ and C₆ are predetermined constants.

Claim 15

The apparatus of claim 14, wherein said second means includes: another function generator for generating data of another preselected function f2 = (C₁+C₂I p +C₃J p ), where C₁, C₂ and C₃ are other predetermined constants; and divider means for finding the Alt p data as a quotient of f1 and f2.

Claim 16

The apparatus of claim 11, wherein the third means includes: means for finding for each layer L between the altitude of point P and the viewpoint VP, the difference in altitude of that layer L from the point P and at least one layer half-fading distance characteristic; and means for using the found layer data to determine the (1/Df eff_cumm ) data.

Claim 17

The apparatus of claim 16, wherein said difference-finding means includes a set of comparators, each determining if the present viewing point altitude is greater than the lower altitude of the associated layer, and encoder means, operating with said comparator set, for providing data denominating the highest layer in which the view point is contained.

Claim 18

The apparatus of claim 17, wherein said difference-finding means further includes multiplexing means for providing Alt L data by selecting altitude data for the lower altitude of the highest contained layer, responsive to the data from said encoder means.

Claim 19

The apparatus of claim 18, wherein the adding means also includes memory means storing at least one intermediate layer quantity data for each layer capable of being addressed by the encoder means data.

Claim 20

The apparatus of claim 16, wherein the layer-data-using means operates in accordance with a function (1/Df eff_cumm_p ) = (1/Df cumm_1 ) + (Alt P -Alt₁) * (1/Df₁) + S * (Alt p -Alt₁)² * (1/2)(1/Df m ), where S = 0 if the viewing point is not in a transitional-density layer and S = 1 if the viewing point is in a transitional-density layer.