Method and apparatus for generating images simulating non-homogeneous fog effects

• US 5,535,374 A
• Filed: 04/17/1995
• Issued: 07/09/1996
• Est. Priority Date: 05/12/1990
• Status: Expired due to Fees

• Current Assignee: Thomson Training & Simulation Limited
• Original Assignee: Rediffusion Simulation Ltd (Thales SA)
• Inventors: Olive, Graham J.
• Primary Examiner(s): Bowler, Alyssa H.
• Assistant Examiner(s): NGUYEN, DZUNG C
• Application Number:
  US08/423,210
• Time in Patent Office: 449 Days
• Field of Search: 395/800, 395/500, 434/36, 434/41, 434/38, 364/DIG. 1
• US Class Current: 703/6
• CPC Class Codes: G06T 15/10 Geometric effects
• CPC Class Codes: G06T 15/50 Lighting effects
• CPC Class Codes: G09B 9/301 by computer-processed or -generated image

Abstract

A method and apparatus for simulating the effect of non-homogeneous fog in an image displayed on a screen. The image is intended to represent the appearance of a model defined in a database in world space coordinates from an eyepoint position in world space, the model being defined in terms of individual features each having predetermined attributes defining the position and visible characteristics of the feature. Image data is derived from the model for each of an array of sampling points distributed across screen space. A non-homogeneous fog structure is defined in world space coordinates as a series of parallel strata of predetermined extinction coefficients. The positions of the eyepoint and a feature to be displayed relative to the fog structure are determined. The distance from the feature to the eyepoint is calculated. An average value of the extinction coefficients between the eyepoint and the feature is calculated from the defined parallel strata, and the attributes are modulated as a function of the calculated distance and the calculated average value of the extinction coefficients.

Claims

1. A method for simulating the effects of non-homogeneous fog in an image displayed on a screen, the image being intended to represent the appearance of a model defined in a database in world space coordinates from an eyepoint position in said world space coordinates, and the model being defined in terms of a plurality of features having predetermined attributes, said method comprising the following steps:

a) defining a non homogeneous fog structure in world space coordinates as a series of parallel strata of predetermined extinction coefficients,

b) determining a position relative to the defined parallel strata of the eyepoint,

c) determining a position relative to the defined parallel strata of a feature which may contribute to the image,

d) determining a distance from the eyepoint to the feature,

e) calculating an average value of the extinction coefficient between the eyepoint and the feature from the defined parallel strata located between the eyepoint and the feature,

f) modulating said attributes as a function of said distance and a calculated average value of the extinction coefficient,

the average value of the extinction coefficient between the eyepoint and the feature being calculated by;

calculating and storing average extinction coefficient values for each of a series of distances from the eyepoint in a direction perpendicular to the parallel strata,

calculating the distance from the eyepoint to the feature in the direction perpendicular to the parallel strata, and

looking up the stored average extinction coefficient corresponding to said distance from eyepoint to feature,

the non-homogeneous fog structure being defined in the model by a series of sample extinction coefficients, each corresponding to the extinction coefficient at a respective one of a series of parallel equally spaced sample planes,

the non-homogeneous fog structure being redefined with reference to the eyepoint by a series of average extinction coefficients each corresponding to the average extinction coefficient between the eyepoint and a respective resample plane, the resample planes being parallel to and equally spaced to the said sample planes and one of the resample planes passing through the eyepoint, and

each resampled average extinction coefficient being stored at an address corresponding to a distance from the eyepoint to the resample plane to which that coefficient is related,

wherein the position of the eyepoint relative to the defined parallel strata is determined from a dot product of a vector representing a direction from the eyepoint to an origin of the parallel strata and a vector representing an axis perpendicular to the parallel strata.

2. A method for simulating the effects of non-homogeneous fog in an image displayed on a screen, the image being intended to represent the appearance of a model defined in a database in world space coordinates from an eyepoint position in said world space coordinates, and the model being defined in terms of a plurality of predetermined feature attributes, wherein said method comprises the following steps:

a) defining a non-homogeneous fog structure in world space coordinates as a series of sample extinction coefficients each corresponding to the extinction coefficient at a respective one of a series of parallel equally spaced sample planes,

b) determining a position relative to the defined parallel planes of the eyepoint,

c) determining a position relative to the defined parallel planes of a feature which may contribute to the image,

d) determining a distance from the eyepoint to the feature in a direction perpendicular to the parallel planes,

e) redefining the non-homogeneous fog structure with reference to the eyepoint by a series of average extinction coefficients each corresponding to a calculated average extinction coefficient between the eyepoint and a respective resample plane, the resample planes being parallel to and equally spaced to the said sample planes and one of the resample planes passing through the eyepoint,

f) storing each calculated average extinction coefficient at an address corresponding to a perpendicular distance from the eyepoint to the resample plane to which that coefficient is related,

g) looking up the stored average extinction coefficient from the address corresponding to said distance from eyepoint to feature, and

h) modulating said attributes as a function of the calculated average extinction coefficient looked up from said address corresponding to said distance from eyepoint to feature.

3. A method as in claim 2, wherein average extinction coefficients are looked up corresponding to two resample planes between which the feature is located, and a further average extinction coefficient is calculated by interpolating the looked-up coefficients with reference to the position of the feature relative to the said two resample planes.

4. A method as in claim 3, wherein screen space is divided into a plurality of cells each covering a plurality of pixels, and wherein, for each feature, said method comprises:

calculating addresses of the resample planes for points defined by the intersections between lines drawn from the eyepoint through the corners of the cells and a plane defined by the feature, and

calculating the resample plane addresses for each of a series of sampling points of the feature by interpolation from the cell corner resample plane addresses.

5. A method as in claim 2, wherein the position of the eyepoint relative to the defined parallel strata is determined from a dot product of a vector representing a direction from the eyepoint to an origin of the parallel strata and a vector representing an axis perpendicular to the parallel strata.

6. Apparatus for simulating the effects of non-homogeneous fog in an image displayed on a screen, the image being intended to represent the appearance of a model defined in a database in world space coordinates from an eyepoint position in said world space coordinates, and the model being defined in terms of a plurality of predetermined feature attributes, wherein said apparatus comprises:

a) means for defining a non-homogeneous fog structure in world space coordinates as a series of sample extinction coefficients each corresponding to the extinction coefficient at a respective one of a series of parallel equally spaced sample planes,

b) means for determining a position relative to the defined parallel planes of the eyepoint,

c) means for determining a position relative to the defined parallel planes of a feature which may contribute to the image,

d) means for determining a distance from the eyepoint to the feature in a direction perpendicular to the parallel planes,

e) means for redefining the non-homogeneous fog structure with reference to the eyepoint by a series of average extinction coefficients each corresponding to a calculated average extinction coefficient between the eyepoint and a respective resample plane, the resample planes being parallel to and equally spaced to the said sample planes and one of the resample planes passing through the eyepoint,

f) means for storing each calculated average extinction coefficient at an address corresponding to a perpendicular distance from the eyepoint to the resample plane to which that coefficient is related,

g) means for looking up the stored average extinction coefficient from the address corresponding to said distance from eyepoint to feature, and

h) means for modulating said attributes as a function of the calculated average extinction coefficient looked up from said address corresponding to said distance from eyepoint to feature.

7. Apparatus as in claim 6, wherein said means for looking up average extinction coefficients generates an average value corresponding to two resample planes between which the feature is located, and a further average extinction coefficient is calculated by interpolating the looked-up coefficients with reference to the position of the feature relative to the said two resample planes.

8. Apparatus as in claim 7, wherein screen space is divided into a plurality of cells each covering a plurality of pixels, and wherein, for each feature, said apparatus comprises:

means for calculating addresses of the resample planes for points defined by the intersections between lines drawn from the eyepoint through the corners of the cells and a plane defined by the feature, and

means for calculating the resample plane addresses for each of a series of sampling points of the feature by interpolation from the cell corner resample plane addresses.

9. Apparatus as in claim 6, including means for determining the position of the eyepoint relative to the defined parallel strata from a dot product of a vector representing a direction from the eyepoint to an origin of the parallel strata and a vector representing an axis perpendicular to the parallel strata.

10. Apparatus for simulating the effects of non-homogeneous fog in an image displayed on a screen, the image being intended to represent the appearance of a model defined in a database in world space coordinates from an eyepoint position in said world space coordinates, and the model being defined in terms of a plurality of features predetermined attributes wherein said apparatus comprises:

a) means for defining a non homogeneous fog structure in world space coordinates as a series of parallel strata of predetermined extinction coefficients,

b) means for determining a position relative to the defined parallel strata of the eyepoint,

c) means for determining a position relative to the defined parallel strata of a feature which may contribute to the image,

d) means for determining a distance from the eyepoint to the feature,

e) means for calculating an average value of the extinction coefficient between the eyepoint and the feature from the defined parallel strata located between the eyepoint and the feature,

f) means for modulating said attributes as a function of said distance and a calculated average value of the extinction coefficient,

said means for calculating an average value including;

means for calculating and storing average extinction coefficient values for each of a series of distances from the eyepoint in a direction perpendicular to the parallel strata,

means for calculating the distance from the eyepoint to the feature in the direction perpendicular to the parallel strata, and

means for looking up the stored average extinction coefficient corresponding to said distance from eyepoint to feature,

the non-homogeneous fog structure being defined in the model by a series of sample extinction coefficients, each corresponding to the extinction coefficient at a respective one of a series of parallel equally spaced sample planes,

the non-homogeneous fog structure being redefined with reference to the eyepoint by a series of average extinction coefficients each corresponding to the average extinction coefficient between the eyepoint and a respective resample plane, the resample planes being parallel to and equally spaced to the said sample planes and one of the resample planes passing through the eyepoint, and

each resampled average extinction coefficient being stored at an address corresponding to a distance from the eyepoint to the resample plane to which that coefficient is related.

11. Apparatus as in claim 10, wherein said means for calculating an average extinction coefficient includes means for looking up two corresponding resample planes between which the feature is located, and calculating a further average extinction coefficient by interpolating the looked-up coefficients with reference to the position of the feature relative to the said two resample planes.

12. Apparatus as in claim 11, wherein screen space is divided into a plurality of cells each covering a plurality of pixels, and wherein, for each feature, said apparatus comprises:

means for calculating addresses of the resample planes for points defined by the intersections between lines drawn from the eyepoint through the corners of the cells and a plane defined by the feature, and

means for calculating the resample plane addresses for each of a series of sampling points of the feature by interpolation from the cell corner resample plane addresses.

13. Apparatus as in claim 10, including means for determining the position of the eyepoint relative to the defined parallel strata from a dot product of a vector representing a direction from the eyepoint to an origin of the parallel strata and a vector representing an axis perpendicular to the parallel strata.