Height-field construction using cross contours. (August 2017)

• Record Type: Journal Article
• Authors: Bui, Tuan Minh; Kim, Junho; Lee, Yunjin
• Is Part Of: Computers & graphics. Volume 66(2017)
• Page Start: 53
• Page End: 63
• Publication Date: 2017-08
• Subjects: Height field construction -- 2D sketches -- 3D-effect shading; Computer graphics -- Periodicals; 006.6
• DOI: 10.1016/j.cag.2017.05.020
• Languages: English
• ISSNs: 0097-8493

Abstract

Highlights: A novel method to construct a height field using cross contours: Our system uses cross contours as a metaphor for constructing a height field from a 2D hand-drawn input. Users can draw sketches without hard constraints or additional understanding about drawing primitives. Unprojection of 2D polygons into 3D space based on properties of polygons: we consider intersecting cross contours as the projection of a 3D polygonal mesh approximating a depicted shape. We also propose an image-space optimization method to obtain 3D edge vectors and 3D normals of the polygons. Height field construction without fixed boundary conditions: Instead of giving specific values as constraints, we constraint the relative height values between the intersection points of cross contours. Graphical abstract: Abstract: We developed an interactive modeling tool for constructing a height field from the cross contours in a line drawing, added to provide an illusion of depth. Our approach places no specific constraints on the artist and can handle freely drawn shapes with partially structured or partially connected cross contours. In our system, the user first draws cross contours across the interior boundaries of the object. The system then extracts the intersection points of the contours and derives 2D polygons by connecting consecutive intersection points with straight lines. These 2D polygons are treated as the projection of a polygonal surface approximating the shape of the object. The 3D edge vectors and 3D normals of the approximated polygon surface are then estimated while considering the perceptions of the viewer and the goals of the designer. Based on the relative height values obtained from the 3D edge vectors and the co-planarities of the curve segments, a height field is generated in the image space that reasonably matches the cross contours of the input drawing. Experimental results demonstrated the ability of the system to generate height fields from a wide range of cross contours. We also showed that our system can be used to apply lighting effects to sketches and allows local shape deformation based on the constructed height field.