GB2455966A

GB2455966A - Generating a Low-Relief Model of an Object

Info

Publication number: GB2455966A
Application number: GB0720986A
Authority: GB
Inventors: Timothy Paul Buck
Original assignee: Delcam Ltd
Current assignee: Delcam Ltd
Priority date: 2007-10-26
Filing date: 2007-10-26
Publication date: 2009-07-01
Anticipated expiration: 2027-10-26
Also published as: GB2455966B; GB0720986D0

Abstract

A system arranged to generate a bas-relief or low-relief model of an object uses a model (fig. 6) (which could comprise a 2.5D model) of the object and a surface-processor arranged to determine the curvature of a plurality of points on the surface. The height of a point in the low relief model (fig. 7) is determined by a function of the surface curvature. A model generation means, e.g. CNC milling machine, is arranged to fabricate the low relief model.

Description

METHOD AND SYSTEM FOR GENERATING LOW-RELIEFS

Field of the invention

This invention provides a system and method for generating low-reliefs.

Background of the invention

Some applications use so-called low reliefs to provide a representation of a 3D object which are not true representations but which provide sufficient information to a viewer's brain to allow the viewer to determine what the object is. An example of such an application is the fabrication of coins which tend to have a bust on one side and another picture on the reverse side.

The height profile of the bust on a coin does not correspond to the height profile of the person on which it is modelled. For example, the nose of the bust is shown to be roughly the same height as the cheek of the person. This is clearly not the case on a real person but this representation provides an image that allows the identity of the person (or other object) to be determined.

However, the creation of such low reliefs is a skilled process currently performed by hand. The process requires a set of skills which are contrary to usual sculpting principles. There may be only a few people in a country that possess the necessary skills to produce such works. It is thought that, at the time of writing, there are on the order of 10 people in the UK that can produce such works.

These techniques can be used on a variety of fields other than coins, such as on jewellery, medals, trophies, etc. Indeed, the techniques may be applied to any field that utilises application of an image have a low height profile to an object.

GB2403883 provides a technique in which a low relief model can be generated from a 2D image.

Summary of the invention

According to a first aspect of the invention there is provided a system arranged to generate a low-relief model of an object, the system comprising a memory arranged to hold a model of an object, a processing circuitry arranged to process the model and a model generation means, the processing circuitry comprising a surface-processor arranged to process the surface of the model of an object to determine the surface curvature of a plurality of points on the surface the processing means being further arranged to generate a low relief model in which the height of a point in the low relief model, corresponding to a point on the object, is given by a function of the surface curvature and wherein the model generation means is arranged to fabricate the low relief model.

Such a system is advantageous as it can provide a low relief from a model which can subsequently be used on an object, such as a coin, jewellery, medals, or the like. As such the generation of such objects is likely to be made easier, cheaper and quicker.

Such low reliefs are often known as bas-reliefs. For the avoidance of doubt low reliefs include any of the following: the representation of a head on a coin, the representations of heads on crockery, seal rings, jewellery, cameos, intaglios, a relief for the memorial industry (for providing reliefs on headstones and the like), etc. Low, or bas, reliefs are advantageous for some arts in which it is desirable to provide a realistic impression of the original article, rather than a true representation of the original. If a 3D model of an object, for example a head, is scaled down so that it can be represented on a coin or the like, then features within the object, such as ears, are often lost.

Thus, in a bas-relief the relative dimensions of the various features within the original are altered relative to one another.

The system may comprise a model generator arranged to generate the model of the object allowing the system to generate a model to be converted into a low-relief model. A manipulator arranged to allow the model to be manipulated may also be provided.

The system may comprise a display arranged to display the model of the object.

The surface-processor may be arranged to determine the surface normal of the points on the surface of the model. In particular, the surface-processor may be arranged to determine the length of the Z component of the surface normal. Such an arrangement may provide a convenient way of determining the surface curvature of that point.

In some embodiments, the surface processor may comprise an illuminator arranged to trace the path of at least one ray, from a source remote from the model, incident upon the model to determine how the ray is reflected from the model's surface in order to determine the curvature of the surface.

In some embodiments, the illuminator may be arranged to position the source of the or each ray normal to a plane through the model of the object. The plane is conveniently parallel to the display on which the model of the object would be displayed if viewed by a user. Such an arrangement is convenient as it allows a user to see the model from which the low-relief will be created.

In other embodiments, the plane may be at inclined at an angle to the display on the which the model of the object would be displayed if viewed by a user. Such an arrangement may prove convenient for applications in which the system is used. One particular application in which such an arrangement might be convenient is the generation of watermarks. In such embodiments, the tracing of a ray may be more convenient than the determination of the surface normal.

Conveniently, the processing circuitry comprises a polygon generator arranged to generate a set of planar tessellating polygons representing the surface of the low-relief model. Such a set of planar polygons is convenient because it provides a convenient manner to represent the surface. Most conveniently, the polygons are triangles. Sets of planar triangles are well known in the field of computer graphics.

The model generation means may comprise a rapid prototyping machine arranged to fabricate a physical representation (i.e. a physical model) of the low-relief model. The use of a rapid prototyping machine is convenient because, as its name suggests, its output is produced rapidly, but is also produced cheaply.

Alternatively, or additionally, the model generation means may comprise a CNC machine arranged to generate a physical representation (i.e. a physical model) of the low-relief model.

The model generation means is optional to the system of the first aspect of the invention.

According to a second aspect of the invention there is provided a method of fabricating a low-relief model of an object, the method comprising: 1. acquiring a computer model of an object to be modelled; ii. causing a surface-processor to process the surface of the computer model to determine the surface curvature of a plurality of points on the surface; iii. causing the processing circuitry to generate a low relief model in which the height of a point in the low-relief model, corresponding to a point on the object. is given by a function of the surface curvature; and iv. fabricating the low-relief model using data generated from the low-relief model.

An advantage of such a method is that it is convenient and allows a low-relief model to be rapidly produced. Further, means for acquiring a computer model are well known are widely available and are now inexpensive and therefore the expense of producing the computer model is reduced.

Conveniently, the model of the object is three dimensional (3D). It is however, conceivable that the model is so-called two and a half dimensional; i.e. 2.5D. Such 2.5D is generally provided by a bit map in which a height is assigned to each pixel. Such pixels having a height are often referred to as voxels.

In some embodiments, the model of the object is 3D within the memory but is converted to 2.5D before processing. In such embodiments, the surface curvature may be determined for each pixel (i.e. voxel) within the 2.5D image.

In order to process the surface curvature of a pixel it may be desirable to process a plurality of pixels adjacent the pixel being processed in order to determine the curvature of the surface at that pixel.

The surface-processor may determine the surface normal of the points on the surface of the model and in particular the surface- processor may determine the length of the Z-component of the surface normal. Such a method may provide a convenient way of determining the surface curvature.

In some embodiments, the surface processor may comprise an illuminator arranged to trace the path of at least one ray, from a source remote from the model, incident upon the model, to determine how the ray is reflected from the model's surface.

In some embodiments, the illuminator may be arranged to trace rays which are normal to a plane through the model of the object.

Conveniently, the plane is parallel to a plane of a display on which the model of the object would be displayed if viewed by a user.

In other embodiments, the plane may be inclined at an angle to the display on which the model of the object would be displayed.

In some embodiments, the height of a point in the low-relief model is given by the length of the Z component of the reflected ray. Additionally, the length of the Z component may be scaled in order to adjust the height of the low-relief. The Z axis is generally taken to be the axis along which the incident ray travels. In other embodiments, the height of a point in the low-relief is given by the angle at which the reflected ray travels to one of the axis (X, Y or Z).

Generally, unit vectors are used to determine the surface normal or the reflected ray such that the length of the X, Y and Z components of the reflected ray are between 0 and 1. The skilled person will appreciate that other co-ordinate systems may be used.

The physical model is preferably produced using a rapid prototyping machine (3D printer), but may use a CNC milling machine, or the like in order to generate the physical model.

Such low reliefs are particularly convenient for certain arts. These arts include the arts of producing coins, producing pottery, stone masonry, water marks, jewellery (including intaglio or cameo), card embossing, security, or similar. Generally, the method may prove to be applicable to arts in which a low relief of human head is required.

The method may comprise fitting a plurality of planar tessellating polygons to cover the surface of the low-relief model. Such an arrangement is advantageous, because it provides a powerful way of representing the surface, whilst aiding the reduction in processing power required to manipulate the low-relief model. Preferably, the polygons are triangles.

Conveniently, the method may comprise generating a physical model from the low-relief model. The physical model may be generated by a CNC milling machine, a rapid prototyping machine (3D printer), or the like.

Commonly known 3D printers include those using sterolithography, selective laser sintering, fused deposition modelling, laminated object modelling, inkjet deposition.

Further, the resulting physical model may be useful for mass production, plastic moulding, pressing, stamping dies, or the like.

The method may ensure that the surface of the low-relief model covered with polygons has no discontinuities (i.e. sometimes known as the polygons being fully connected), or areas not covered by a polygon, therein, i.e. is what is termed in the art as "watertight". Such an arrangement is particularly convenient if a physical model is to be generated, especially, if it is to be generated using a rapid prototyping machine. If there are areas not covered by polygons, these can lead to excess material being added during fabrication of the physical model, or the 3D printer may simply stop and not be able to produce the model.

In other embodiments the method may generate slices through the model.

Such slices are convenient for driving some types of machine and are therefore convenient to allow the method to drive a plurality of machines.

Fabrication of a low-relief model is an optional feature of the second aspect of the invention.

According to a third aspect of the invention there is provided a machine readable medium containing instructions to cause a computer to function as the system of the first aspect of the invention when programmed thereon to.

According to a fourth aspect of the invention there is provided a machine readable medium containing instructions to cause a computer to perform the method of the second aspect of the invention when programmed thereonto.

The machine readable medium of the third or fourth aspects of the invention may comprise any one or more of the following: a floppy disk, a CDROM, a DVD ROM/RAM (including +RW, -RW), an HD DVD, a BLU Ray disc, a hard drive, a non-volatile memory, any form of magneto optical disk, a wire, a transmitted signal (which may comprise an internet download, an ftp transfer, or the like), or any other form of computer readable medium.

According to a fifth aspect of the invention there is provided an object produced by the method of the second aspect of the invention.

The object may be any one of the following: the representation of a head on a coin, the representations of heads on crockery, seal rings, jewellery.

cameos, intaglios, a relief for the memorial industry (for providing reliefs on headstones and the like).

Brief description of the drawings

There now follows, by way of example only, a description of an embodiment of the present invention with reference to the accompanying drawings, of which: Figure 1 schematically shows a computer system such as may be used in some embodiments of the invention; Figure 2 schematically shows the memory of a processing unit arranged to provide an embodiment of the invention; Figure 3 shows a CNC machine arranged to fabricate a low-relief model; Figure 4 shows a rapid prototyping machine arranged to fabricate a low-relief model.

Figure 5 shows a flow chart outlining the steps of one embodiment of the present invention; Figure 6 shows four views of a 3D computer model of an object; and Figure 7 shows low-relief models each one of which has been generated from a view of Figure 6;

Detailed description of the drawings

The computer system of Figure 1 comprises a display 102, processing circuitry 104, a keyboard 106 and a mouse 108. The processing circuitry 104 comprises a processing unit 112, a graphics system 113, a hard drive 114, a memory 116, an I/O subsystem 118 and a system bus 120. The processing unit 112, graphics system 113 hard drive 114, memory 116 and I/O subsystem 118 communicate with each other via the system bus 120, which in this embodiment is a PCI bus, in a manner well known in the art.

The graphics system 113 comprises a dedicated graphics processor arranged to perform some of the processing of the data that it is desired to display on the display 102. Such graphics systems 113 are well known and increase the performance of the computer system by removing some of the processing required to generate a display from the processing unit 112.

It will be appreciated that although reference is made to a memory 116 it is possible that the memory could be provided by a variety of devices.

For example, the memory may be provided by a cache memory, a RAM memory, a local mass storage device such as the hard disk 114, any of these connected to the processing circuitry 104 over a network connection. However, the processing unit 112 can access the memory via the system bus 120 to access program code to instruct it what steps to perform and also to access data to be processed. The processing unit 112 is arranged to process the data as outlined by the program code.

A schematic diagram of the memory 114,116 of the computer system is shown in Figure 2. It can be seen that the memory comprises a program storage portion 200 dedicated to program storage and a data storage portion 202 dedicated to holding data.

The program storage portion 200 comprises a model generator 206 which is used, by a user, to generate a model of an object 204. In the embodiment being described the model generator 206 is provided by CAD software such as the ARTCAMTM package provided by the applicant.

Also provided within the program storage portion 200 is a manipulator 208 which allows a user to manipulate the model of the object 204. For example, the manipulator 208 allows the user to rotate the model about any of the X, Y and Z axis to allow a user to display a view of the model 204 that he/she wishes to convert into a low-relief. The manipulator 208 also allows a user to translate the model, scale the model to stretch it in one or more dimensions. The manipulator 208 may alter the model of the object 204 or simply cause it to be displayed differently on the display 102. The manipulator may be provided by the same software as the model generator.

A surface-processor 209 is provided which is arranged to determine the surface curvature of the surface of the model at any point on the surface.

In one embodiment, this is performed by determining the surface normal of the surface at that point and determining the length of the Z component of the surface normal, with the surface normal taken to be a unit vector.

An illuminator 210 is also provided which is arranged to perform a ray tracing algorithm, and to trace the path of at least one ray, from a virtual source, which is remote from the model. In many embodiments, this may alternatively be used to determine the surface normal and in these embodiments the algorithm positions the virtual source perpendicular to the plane of the display 102 such that rays traced thereby each arrive perpendicular to the display; i.e. the rays are parallel to one another.

Thus, rays traced from the source impinge upon the model of the object 204 as the user has caused to be displayed upon the display 102 using the manipulator 208.

In some embodiments, the position of the virtual light source can be moved such the reflected ray may no longer correspond to the surface normal. Such embodiments, may be advantageous for certain applications such as the generation of water marks.

A polygon generator 212 is also provided which is arranged to polygonise the surface of the low-relief model 212. In particular the polygon generator 212 covers the surface of the low-relief model in a mesh of triangles which are so-called water tight. Such water-tightness ensures that there are no gaps in the mesh and that the model is suitable for use with a machines such as a rapid prototyping machine.

In one embodiment of the invention, the model generation means comprises a CNC milling machine 300 as shown in Figure 3. In such an embodiment, the low-relief model is formed from a block of material 302.

A material removal tip 304 removes material from the block 302 and is controlled by processing circuitry 104. In other embodiments, the CNC milling machine 300 may be controlled by a separate processing circuitry which receives data from the processing circuitry 104.

In a further embodiment of the invention, the model generation means comprises a rapid prototyping model such as a 3D printer 400. The 3D printer 400 is controlled by the processing circuitry 104 but again, the printer 400 may be controlled by a separate processing circuitry which is arranged to receive data from the processing circuitry 104. It will be appreciated that some types of rapid prototyping machine are suitable for generating a final product (typically those that use a plastics material or a material having a metal content) although other rapid prototyping machines are only suitable for producing prototypes.

The method of using the apparatus previously described will now be described with the aid of Figure 5. In a first step of the method 500 a model of an object 204 is acquired into the data storage portion 202 of the memory 114, 116. Acquisition can be a variety of techniques, such as creating the model using the model generator 206, inputting the data into the data storage portion 202 via the I/O subsystem 118, scanning an image using a scanning means which might be a probing system or any other suitable technique.

Once the model of the object 204 has been acquired it may be viewed upon the display 102 and manipulated using the manipulator 208. Using the manipulator 208 a user is able to manipulate the computer model 204 to present a desired view of the object 502.

In one example, as exemplified in the view of Figure 6 the computer model is a person's head. Figure 6 shows four views 600 a to d of the computer model. Each of the four views is a view of the computer model from a different angle which have been produced by use of the manipulator 208, in this example, to rotate the model about an axis passing along the neck of the person's head. Other manipulations are possible and only one manipulation has been shown for reasons of conciseness. Moreover, generally only single view of the model 204 would be viewed on the display 102 at any one time. Four views have been shown in Figure 6 for clarity reasons Once the user has manipulated the model to provide a desired view on the display 102 the processing circuitry is caused to perform an analysis of the surface curvature of the model. In the embodiment being described, this is achieved by assessing the surface normal at a plurality of points on the surface of the model 504. In order to perform this determination of the surface normal, it is convenient to convert the model into a 2.5D model and calculate a surface normal for every voxel of the 2.5D model.

The skilled person will appreciate that it can be convenient when determining the surface normal to consider a number of voxels adjacent the voxel for which the normal is being determined in order to determine the nature of the surface at the voxel being processed.

In the embodiment being described the length of the Z axis component of the surface normal is determined 506. The axes are shown on Figure 6 at reference number 602.

In other embodiments, a ray tracing algorithm might be used on the model using the surface processor 209 and the illuminator 210 in order to determine the surface curvature. In such an embodiment, the length of the Z axis component of a reflected ray, as determined by ray tracing, may be calculated. In other embodiments, the angle of the reflected ray, as determined by ray tracing using the illuminator 210, from any one of the axes is determined. Generally, the angle from the Z axis would be used.

The Z axis height obtained, by the surface processor 209 or illuminator 210 is converted 508 into a Z axis height for a point on a low-relief model which corresponds with the point upon the model of the object 204. Thus, a low-relief model 212 of the object is generated and stored within the data storage portion 202 of the memory. The surface normal or the reflected ray is a unit vector and as such the length of the Z axis component lies in the range 0 to 1. The height of the low-relief may be scaled in order to provide the desired thickness of the low-relief.

Examples of the low-relief model 212 are shown in Figure 7 which four such low-relief models 700a-d. Each of the low-relief models 700a-d is generated from the view of the model of the object shown in Figure 6 having the same letter. For example, view 600a of the object corresponds with the low relief model 700a.

Once the low relief has been generated, the path generator 214 can be used, in step 510, to generate tool path data to control the CNC machine 300. Alternatively, or additionally, the path generator 214 can be used to generate data to control the rapid prototyping machine 400.

In a final step 512 of the method, the CNC 300 and/or the rapid prototyping machine 400 creates the low-relief from the tool path data generated by the path generator 214.

As well as, or instead of generating the low-relief, the method, in step 14, may render the low-relief model and subsequently display 516 the low-relief model on the display 102.

In some embodiments, the 2.5D model that has been used to generate the low-relief may be scaled in thickness and subsequently be merged with the low-relief. Such a step may provide an enhanced low relief since it can help to return some curvature to the low relief which has been lost in the initial steps of the method. The merging of the model and the low-relief may be provided by a simple addition of the heights of the two.

Generally the scaling will be a reduction in thickness, but it could be a 1 to 1 scaling or indeed a thickening.

This model fabricated by the CNC machine or the rapid prototyping machine may be the result of the process, or the model may itself be used for additional steps (such as investment casting, or the like).

It will be appreciated that the process is not limited to images of faces, and that a vast number of objects could be modelled in this way. For example, the process may be used to model buildings or other man made structures, logos (including company logos), landmarks and landscapes, (including satellite scans of landmarks and landscapes), animals, etc. Using this process enables detailed and accurate models to be produced with greater rapidity and less artistic skill than has previously been possible with traditional methods.

Claims

I CLAIMS

1. A system arranged to generate a low-relief model of an objects the system comprising a memory arranged to hold a model of an object. a processing circuitry arranged to process the model and a model generation means, the processing circuitry comprising a surface-processor arranged to process the surface of the model of an object to determine the surface of a plurality of points on the surface, the processing means being further arranged to generate a low relief model in which the height of a point in the low relief model, corresponding to a point on the object, is given by a function of the surface curvature and wherein the model generation means is arranged to fabricate the low relief model.

2. A system according to claim 1 which comprises a model generator arranged to generate the model of the object.

3. A system according to claim 1 or 2 which comprises a manipulator arranged to allow the model to be manipulated.

4. A system according to any preceding claim in which the surface-processor is arranged to determine the surface normal of the points on the surface of the model.

5. A system according to claim 4 in which the surface processor is arranged to determine the length of the Z component of the surface normal.

6. A system according to any preceding claim in which the surface processor comprises an illuminator arranged to trace the path of at least one ray, from a source remote from the model, incident upon the model to determine how the ray is reflected from the model's surface.

7. A system according to claim 6 in which the illuminator is arranged to position the source of the or each ray normal to a plane through the model of the object.

8. A system according to claim 6 or 7 which comprises a display arranged to display the model of the object.

9. A system according to claim 8 as it depends from claim 7 in which the plane is parallel to the display on which the model of the object is displayed.

10. A system according to any preceding claim in which illuminator is arranged to determine the height of a point on the low-relief according the length of the Z axis component of the reflected ray.

11. A system according to any preceding claim which comprises a polygon generator arranged to generate a set of planar tessellating polygons representing the surface of the low-relief model.

12. A system according to any preceding claim in which the model generation means comprises a rapid prototyping machine.

13. A system according to any of claims 1 to 11 in which the model generation means comprises a CNC machine.

14. A method of fabricating a low-relief model of an object, the method comprising: i. acquiring a computer model of an object to be modelled; ii. causing a surface-processor to process the surface of the computer model to determine the surface curvature of a plurality of points of the surface; iii. causing the processing circuitry to generate a low relief model in which the height of a point in the low-relief model, corresponding to a point on the object, is given by a function of the surface curvature; and iv. fabricating the low-relief model using data generated from the low-relief model.

15. A method according to claim 14 in which the model of the object is three dimensional (3D) and is converted to 2.5D or in which the model is 2.5D in which a point is processed on the surface for substantially every pixel of the 2.5D model.

16. A method according to claim 14 or 15 in which the surface-processor determines the surface normal of the points on the surface of the model.

17. A method according to claim 16 in which the surface-processor determines the length of the Z-component of the surface normal.

18. A method according to any of claims 14 to 17 in which the surface-processor comprises an illuminator arranged to trace the path of at least one ray, from a source remote from the model, incident upon the model, to determine how the ray is reflected from the model's surface.

19. A method according to claim 18 in which the illuminator traces one or more rays which are normal to a plane through the model of the object.

20. A method according to claim 19 in which the plane is parallel to a plane of a display on which the model of the object is displayed.

21. A method according to any of claims 18 to 20 in which the height of a point in the low-relief model is given by the length of the Z component of the reflected ray.

22. A method according to any of claims 14 to 21 in which the physical model produced using a rapid prototyping machine or a CNC machine.

23. A method according to any of claims 14 to 22 which comprises fitting a plurality of planar tessellating polygons to cover the surface of the low-relief model.

24. An object produced by the method of any of claims 14 to 23.

25. An object according to claim 24 which is any one of the following: the representation of a head on a coin, the representations of heads on crockery, seal rings, jewellery, cameos, intaglios, a relief for the memorial industry.

26. A system arranged to generate a low-relief model substantially as described herein.

27. A method of fabricating a low-relief model substantially as described herein.