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Process for eliminating hidden faces for synthesis of a three-dimensional wire image

  • US 5,125,074 A
  • Filed: 08/10/1989
  • Issued: 06/23/1992
  • Est. Priority Date: 08/10/1988
  • Status: Expired due to Fees
First Claim
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1. A process for eliminating hidden faces for synthesis of a three-dimensional wire image wherein said wire image consists of facets, each facet consisting of edges each represented by the coordinates of its ends and by the value of its slope, in a Cartesian system of coordinates of two axes of coordinates, each point of an edge being provided with a priority parameter making it possible to restore the appearance of a third dimension, on a two-dimension display, said process comprising the steps of:

  • extracting data from a data base to determine the facets which will represent an object in wire form;

    performing a geometric transformation on each of said facets to place it in a Cartesian system of coordinates which is the coordinates of the observer of the synthesis image and no longer the coordinates corresponding to the calculations made in order to provide the data base;

    performing a cutting to eliminate the facets which will be outside the observer'"'"'s field of vision wherein said field of vision has the shape of a pyramid whose vertex is the observers eye;

    providing a projection of said facets on a display plane by a homothetic transformation whose ratio is a function of the distance between the observer and the point to be projected on the screen and also a function of the distance between the observer and the screen;

    determining intersection points of all edges by;

    cutting a set of ordinate values into intervals so that each bound is the ordinate value of an edge end and so that no ordinate of an edge end is in said intervals;

    determining, for each interval, the coordinates of intersection points of edges whose ordinates are in said intervals;

    constituting, for each edge, a list of the intersection points of said each edge with other of said edges of higher priority wherein said list is arranged according to the position of points of intersection between a first and second edge end;

    determining, for each intersection point the value of an indicator indicating if the facet of the higher priority edge masks the least priority edge, from the intersection point considered;

    or masks it before the intersection point considered;

    or else masks it before and after the intersection point;

    each edge being scanned from a first to a second end;

    determining, for a first end of each image, a number of facts which mask said first end;

    determining, for each edge, the segments of said each edge which are visible and those that are hidden, by determining a number of facets that mask each segment, based on said number of facets which mask said first end of the edge, and based on the values of the indicators for said points of intersection of said each edge with most priority edges whereby the hidden parts of said facets are able to be eliminated; and

    displaying on a display device the image obtained by calculating the actuating signals corresponding to each edge segment that is to be lit up on the screen.

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