Method and apparatus for preparing a perspective view of an approximately spherical surface portion

• US 6,618,049 B1
• Filed: 11/04/2002
• Issued: 09/09/2003
• Est. Priority Date: 11/30/1999
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: Silicon Graphics Incorporated (Graphics Properties Holdings, Inc.)
• Inventors: Hansen, Paul Edward
• Primary Examiner(s): Zimmerman, Mark
• Assistant Examiner(s): Nguyen, Kimbinh T.
• Application Number:
  US10/288,661
• Time in Patent Office: 309 Days
• Field of Search: 345/423, 345/427, 345/428, 345/581, 345/582, 345/586, 345/607
• US Class Current: 345/423
• CPC Class Codes: G06T 15/20 Perspective computation

Abstract

A computer system (10) can prepare and present on a display (22) a two-dimensional image that includes a perspective view, from a selected eyepoint (71, 152), of an object (23) which is a three-dimensional object of an approximately spherical shape, such as the earth. The system maintains image information for the object at each of several different resolution levels, portions of which are selected and mapped into the perspective view for respective portions of the surface of the object. In order to determine what resolution level to use for a given section of the surface of the object, the system relies on a combination of a logarithm of the square of a distance from the eyepoint to a point on the surface section, and a logarithm of the square of the degree of tilt of the surface section in relation to the eyepoint. In order to determine how far to conceptually tessellate or subdivide the surface of the object, the system relies on the logarithm of the square of the distance from the eyepoint to the point on the surface section.

Claims

1. A method for preparing a perspective view of a surface section having an approximately spherical curvature, comprising:

subdividing a surface section into a first plurality of subsections;

selecting a subsection from the first plurality of subsections;

determining whether the selected subsection is to be further subdivided;

selecting a resolution corresponding to the selected subsection in response to a determination that no further subdividing is to be performed;

mapping image data of the selected subsection into a perspective view for display in response to the selected resolution.

2. The method of claim 1, further comprising:

subdividing the selected subsection into a second plurality of subsections in response to a determination that further subdividing is to be performed;

selecting a subsection from the second plurality of subsections;

determining whether the selected subsection from the second plurality of subsections is to be further subdivided.

3. The method of claim 2, further comprising:

successively subdividing selected subsections until a determination is made that no further subdividing is needed.

4. The method of claim 1, further comprising:

determining a plurality of resolution values for the selected subsection;

selecting one of the resolution values for use in mapping the image data of the selected subsection into the perspective view.

5. The method of claim 4, wherein each resolution value is a function of a distance from an eyepoint to an associated vertex of the selected subsection.

6. The method of claim 4, further comprising:

setting any negative resolution values to zero;

determining whether all of the plurality of resolution values fall within a desired range.

7. The method of claim 1, further comprising:

determining a plurality of tesselation values for the selected subsection;

determining whether any of the plurality of tessellation values exceed a threshold;

initiating generation of the perspective view in response to any of the tesselation values exceeding the threshold.

8. The method of claim 1, further comprising:

determining a plurality of tesselation values for the selected subsection;

determining whether any of the plurality of tessellation values exceed a threshold;

subdividing the selected subsection into a second plurality of subsections.

9. The method of claim 8, wherein each tessellation value is a function of a degree of tilt of the selected subsection relative to an eyepoint.

10. The method of claim 1, further comprising:

partitioning the selected subsection into a plurality of portions;

mapping each of the plurality of portions into the perspective view.

11. A computer readable medium including code for preparing a perspective view of a surface section having an approximately spherical curvature, the code operable to:

subdivide a surface section into a first plurality of subsections;

select a subsection from the first plurality of subsections;

determine whether the selected subsection is to be further subdivided;

select a resolution corresponding to the selected subsection in response to a determination that no further subdividing is to be performed;

extract image data from the selected subsection in response to the selected resolution;

map image data of the selected subsection into a perspective view for display.

12. The computer readable medium of claim 11, wherein the code is further operable to:

determine a plurality of tesselation values for the selected subsection;

determine whether any of the plurality of tessellation values exceed a threshold;

initiate generation of the perspective view in response to any of the tesselation values exceeding the threshold;

subdivide the selected subsection into a second plurality of subsections in response to none of the tesselation values exceeding the threshold.

13. The computer readable medium of claim 12, wherein each tessellation value is a function of a logarithm of a square of a degree of tilt of an associated vertex of the selected subsection relative to an eyepoint.

14. The computer readable medium of claim 11, wherein the code is further operable to:

determine a plurality of resolution values for the selected subsection;

set any negative resolution values to zero;

determine whether all of the plurality of resolution values fall within a desired range;

select one of the resolution values for use in mapping the image data of the selected subsection into the perspective view in response to all of the plurality of resolution values falling within the desired range.

15. The computer readable medium of claim 14, wherein each resolution value is a function of a logarithm of a square of a distance from an eyepoint to an associated vertex of the selected subsection.

16. A system for preparing a perspective view of a surface section having an approximately spherical curvature, comprising:

means for subdividing a surface section into a first plurality of subsections;

means for selecting a subsection from the first plurality of subsections;

means for determining whether the selected subsection is to be further subdivided;

means for selecting a resolution corresponding to the selected subsection in response to a determination that no further subdividing is to be performed;

means for extracting image data from the selected subsection according to the selected resolution means for mapping the image data of the selected subsection into a perspective view for display.

17. The system of claim 16, further comprising:

means for determining a plurality of resolution values for the selected subsection;

means for setting any negative resolution values to zero;

means for determining whether all of the plurality of resolution values fall within a desired range;

means for selecting one of the resolution values for use in mapping the image data of the selected subsection into the perspective view in response to all of the plurality of resolution values falling within the desired range.

18. The system of claim 17, further comprising:

means for selecting a plurality of vertices in the selected subsection;

means for calculating a resolution value at each of the selected vertices, the resolution value being a function of a logarithm of a square of a distance from an eyepoint to an associated vertex of the selected subsection.

19. The system of claim 17, further comprising:

means for determining a plurality of tesselation values for the selected subsection;

means for determining whether any of the plurality of tessellation values exceed a threshold;

means for initiating generation of the perspective view in response to any of the tesselation values exceeding the threshold;

means for subdividing the selected subsection into a second plurality of subsections in response to none of the plurality of tesselation values exceeding the threshold.

20. The system of claim 19, further comprising:

means for selecting a plurality of vertices in the selected subsection;

means for calculating a tesselation value at each of the selected vertices, the tesselation value being a function of a logarithm of a square of a degree of tilt of the selected subsection relative to an eyepoint at an associated vertex.