OA18946A

OA18946A - Coded information means located on an infrastructure to be decoded by sensors located on mobiles

Info

Publication number: OA18946A
Application number: OA1201800328
Authority: OA
Inventors: Alejandro BADOLATO MARTIN
Original assignee: Auto Drive Solutions S.L.
Filing date: 2016-03-02
Publication date: 2019-10-28

Abstract

Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adequate sensor, to read, decode and transform it immediately into information on its exact position in the infrastructure and being characterised by the fact that along the same trajectory described by a mobile it is possible to encode information in the infrastructure by means of different objects presenting dielectric change boundaries or dielectric/metal boundaries at different heights or distances regarding the origin of the onboard sensor, these boundaries being interrogated by a sensor on board the mobile by means of pressure or electromagnetic waves and by measuring the time the waves take to return to the sensor, making it possible to determine the distance at which the reflections occur and in this way to extract the information.

Description

CODED INFORMATION MEANS LOCATED ON AN INFRASTRUCTURE TO BE DECODED BY SENSORS LOCATED ON MOBILES

DESCRIPCIÔN

OBJECT OF THE INVENTION

The invention proposed refers to encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure.

These encoded information means allow for their use, among others, in automatic guiding Systems on ail types of mobile travelling along infrastructures, such as automobile vehicles, railway vehicles or even river vehicles.

FIELD OF THE INVENTION

The field of the invention is that of the automotive auxiliary industry, the railway industry and the electronic industry.

BACKGROUND TO THE INVENTION

A background does exist regarding devices performîng the same function of encoded information which can be located on an infrastructure.

From among these the inventor is similarly the inventer of international patent PCT/ES2015/070378 in which the encoding means is described as a guide rail installed flush with the surface of the road although it can optionally be hidden under a layer of tarmac treated with a layer of hydrophobie material with preferred dimensions of 1.5 cm wîde and 5 cm deep and where the internai part has machined cavities, with the preferred shape of the cavities being that of dihedrons as the planes of dihedrons increase the signal reflected therefore enabling their détection.

This device is efficient for some infrastructures, but it does not allow for exploiting ail

the possibilités offered by the system, for which reason the invention proposed présents other new means adapted very particularly to ail types of infrastructures in existence while also offering more simple means, for example discontinuous and économie, for example paint marks, to encode the information.

On the part of the inventor no antécédent is known to include the provisions presented by this invention, or the advantages such provision implies.

DESCRIPTION OF THE INVENTION

The invention proposed refers to encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform rt immediately into information on rts exact position in the infrastructure.

Among others, these encoded information means allow for their use in automate guiding Systems on ail types of mobile travelling along infrastructures, such as automobile vehides, railway vehides or even river vehides.

The information is given by means of the detedion of changes in the dielectric properties of the means located in an infrastructure, in which the dielectric changes are detected by means of sensors such as a high resolution radar device or another similar detector.

Throughout the trajectory described by a mobile it is possible to encode information in the infrastructure by means of different objects presenting dielectric change boundaries or dielectric/metal boundaries at different heights or distances regarding the origin of the onboard sensor.

These boundaries are interrogated by a sensor on board the mobile by means of pressure or electromagnetic waves and by measuring the time the waves take to retum to the sensor, it is possible to détermine the distance at which the refiections occur and in this way to extract the information.

The following can be drstinguished within the different means:

An information means of these characteristics refers to the information given by the railway sleepers as these present several unique characteristics:

- a uniform surface with regard to the ballast, or

- a different height regarding the track set on a concrète slab

The sleepers are always found at a spécifie distance from a known point on the locomotive(s) or one of the wagons (coaches).

Moreover, these sleepers can be encoded with a series of bits by means of a series of studs of different heights, with the sleeper being encoded by means of a series of studs which offer a series of levels and these studs being covered with a material permeable to the waves and of a known thickness.

The information on the position is divided into 4-bit groups which are encoded successively at each sleeper by means of the levels.

When 2 consecutive bits of the same level are encoded, a third level of a different height is used to encode this second repeated bit.

This technique allows for the sensor to identify both bits and to détermine that the second bit has the same logical level as the previous one.

By altematively using the répétition level it is possible to idenüfÿ consecutive 4-bit strings with the same logical level.

A fourth height level is always used as the fifth bit.

In this way the sensor is capable of knowing the reading direction.

If the first détection matches the fourth level the sensor will detect that it is reading the bits in reverse order.

bits of information obtain 24=16 different sleepers each encoding 5 bits (4 of information and 1 indicating the read in g direction).

A seventeenth sleeper mode! characteristic for its first bit starting with a répétition bit and its fifth bit indicating the reading direction is used to indicate the start or end of a word made up by 4-bit groups.

In this way, a word start sleeper and 8 more sleepers of information encode 232 possible combinations that can be uniquely assigned to the segment occupied by the 9 sleepers.

The information is encoded redundantly in two different places for two sensors to be able to read the information means simultaneously.

The sensor intenogates the infrastructure with a spot 8mm in diameter and in order for each stud to be illuminated correctly by the sensor, the surface area of the studs is 1 cm2, with the height séparation of each stud associated with a different logical level being 0.5 cm.

These studs are covered with a material (2) permeable to waves of a known thickness and has two fonctions: on the one hand to avoid any material from being deposited between the studs and also to serve as reference to détermine the different logical levels.

The locomotive or coach can vary its height due to the action of the suspension but, given that the sensor detects a reflection in the boundary between the permeable material and the air, this can détermine the location of the different logical levels independently from the distance of the locomotive to the ground.

Another information means is also a sleeper but one tn which the information is encoded by slits instead of studs in such a way the sleeper shows no relief on its upper surface.

The stud or slit techniques described may also be used on tracks set on a concrète slab.

Another information means are encoded bîocks but ones that are installed on the sides or the upper part of the trajectory (for example on the catenary, on the arch of a station or tunnel, etc.) tumed round appropriately for their encoded part to face the sensor and arranged at a certain height in such a way there is direct view between the sensor and the block even under snow conditions.

The boundary surfaces can form trihedrons to maximise reflection.

If the information is required for land infrastructures and more specifically roads a sequence of specks/lines of paint or another material is foreseen preferably in colour black so as not to confuse drivers.

The specks present different thicknesses with 2 mm séparations between boundaries and are stuck longitudinally on the road in the centre/lane.

These specks each hâve a surface area of 1 cm2 and present an upper coating of another permeable material with hydrophobie properties which serves as a reference point for the sensor.

The information is also encoded by means of different levels with 3 mm séparations and in 4-bit groups plus a fifth bit indicating the reading direction.

Between the 5-bit blocks there is a free uncoded space for the water to follow the slope marked by the camber of the road so it does not accumulate next to the information means.

Accompanying the sequence of specks, 2 side bands of different thicknesses serve to encode the latéral drift of the sensor with regard to the information means where the information is encoded.

Another information means is made up by a strip with slits of different depths, preferably out of plastic and with each centimètre encoded.

This strip, among other applications, serves to infbrm on the advance and the position to a mobile in such a way this can apply controlled accélérations and décélérations thus enabling the mobile to stop precisely.

An example could be the train stopping at a station.

Another way of encoding information consiste in using objecte (continuous or discontinuous) of the same thickness and permeable to the waves with different transmission properties with regard to propagation speed.

In the case of electromagnetic waves, a different dielectric constant will delay more or less the détection associated with the second dielectric change boundary (back surface of the object).

Another information means is characterised for having the covered surface made up by materials in which the wave propagation speed is different

This fact causes (when considering a constant propagation speed) the détections of upper boundaries to be distanced in a different manner from the détections of the rear boundaries.

Another information means is characterised for having the coating made up by materials in which wave propagation speed is different and due to which, when considering a constant propagation speed, there is a différence between the détection of the boundaries.

such blocks and the corresponding lower ones are different, causîng the détection of the upper boundaries to be different from the détection of the lower boundaries according to the material used.

A solution is proposed making it possible to read encoded information on a nonconductive material by means of the existence or not of dielectric constant change boundaries in the middle that can be detected by means of sensors installed on mobiles.

The dielectric change boundaries În a non-conductive material lead to part of the energy irradiated towards the material in question to be reflected.

This reflected energy is detected by the associated sensor making it possible to

R détermine the radial distance at which the discontinuity is found.

The dielectric change boundaries can be obtained by using two materials or substances whose dielectric constants are different or using a single material in which the boundary is established between the material and the vacuum or the material or a gas or substance.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention two pages of diagrams are attached showing the following:

FIGURE 1. Representing a side view (view perpendicular to the trajectory of the tracks and parallel to the ground) of a sleeper (T) and the encoding means.

FIGURE 2. Representing a side view of the cross-section perpendicular to the axis of the wearing course of a land infrastructure and with the encoding means in blocks.

FIGURE 3. Representing a side view of the cross-section perpendicular to the axis of the wearing course of a land infrastructure and with the encoding means with a different material thickness.

FIGURE 4. Representing a side view of the cross-section perpendicular to the axis of the wearing course of a land infrastructure and with the encoding means in blocks having different propagation speeds.

PREFERENTIAL EXECUTION OF THE INVENTION

The invention proposed refers to encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform rt immediately into information on its exact position in the infrastructure.

The information is given by means of the détection of changes in the dielectric properties of the means located in an infrastructure, in which the dielectric changes are detected by means of sensors such as a high resolution radar device or another similar detector.

These boundaries are interrogated by a sensor on board the mobile by means of pressure or electromagnetic waves and by measuring the time the waves take to retum to the sensor, it is possible to determine the distance at which the reflections occur and in this way to extract the information.

The following can be distinguished within the different means:

A) An information means of these characteristics which we will call type a) refers to the information given by the railway sleepers (T) as these present several unique characteristics:

- a uniform surface with regard to the ballast, or

- a different height regarding the track set on a concrète slab

The sleepers (T) are found at a spécifie distance from a known point on the locomotive(s) or one of the wagons (coaches).

Moreover, these sleepers can be encoded with a sériés of bits by means of a sériés of studs of different heights, as shown in figure 1.

The encoding of the sleeper (T) is performed by means of a sériés of studs which offer a sériés of levels (3), (4), (5) and (6) and these studs are covered with a material (2) permeable to the waves and of a known thickness.

The information on the position is divided into 4-bit groups which are encoded successively ai each sleeper by means of the levels (3 and 4).

When 2 consecutive bits of the same level are encoded, a third level of a different height (5) is used to encode this second repeated bit.

This technique allows for the sensor to identify both bits and to déterminé that the second bit has the same logical level as the previous one.

By alternatively using the répétition level it is possible to identify consecutive 4-bit strings with the same logical level.

A fourth height level (6) is always used as the fifth bit

In this way the sensor is capable of knowing the reading direction.

bits of information obtain 24=16 different sleepers each encoding 5 bits (4 of information and 1 indicating the reading direction).

A seventeenth sleeper model characteristic for its first bit starting with a répétition bit (5) and its fifth bit indicating the reading direction (6) is used to indicate the start or end of a word made up by 4-bit groups.

The sensor interrogates the infrastructure with a spot 8mm in diameter.

In order for each stud to be illuminated conectly by the sensor, frie surface area of the studs is 1 cm2.

The height séparation of each stud associated with a different logical level is 0.5 cm.

These studs are covered with a material (2) permeable to waves of known thickness.

This coating has two functions:

On the one hand to avoîd any material from being deposrted between the studs and also to serve as reference to détermine the different logical levels.

The locomotive or coach can vary its height due to the action of the suspension but, given that the sensor detects a réfection in the boundary between the permeable material and the air, this can détermine the location of the different logical levels independently from the distance of the locomotive to the ground.

B) Another information means we will call type b) is a sleeper in which the information is encoded by slits instead of studs in such a way the sleeper shows no relief on its upper surface.

C) Another information means we will call type c) consists in using the stud or slit techniques on tracks set on a concrète slab.

D) Another information means we will call type d) refers to blocks encoded in an analogous manner to type a) only installed on the sides or the upper part of the trajectory (for example on the catenary, on the arch of a station or tunnel, etc.) tumed round appropriately for their encoded part to face the sensor and arranged at a certain height in such a way there is direct view between the sensor and the block even under snow conditions.

The boundary surfaces can form trihedrons to maximise réfection.

E) Another information means we call type e) is an information means similar to type a) only to be used on roads instead of sleepers.

In this case the studs are a sequence of specks/lines of paint or another material is foreseen preferably in colour black so as not to confuse drivers.

Figure 2 shows a cross section of the wearing course of the road (7) and one of the specks.

The information is also encoded by means of 3 different levels (9-11) with 3 mm séparations and in groups plus a fifth bit (12) indicating the readîng direction.

Accompanying the sequence of specks, 2 side bands (13,14) of different thicknesses serve to encode the latéral drift of the sensor with regard to the information means where the information is encoded.

F) Another information means called type f) is made up by a strip with slits of different depths (with the levels defined in type a), preferably out of plastic and with each centimètre encoded.

This strip, among other applications, serves to inform on the advance and the position to a mobile in such a way this can apply controlled accélérations and décélérations thus enabling the mobile to stop precisely.

An example could be the train stopping at a station.

G) Another way of encoding information we call type g) consists in using objects (continuous or discontinuous) of the same thickness and permeable to the waves with different transmission properties with regard to propagation speed.

H) Another way of encoding information we call type h), in accordance with figure 3 and consisting in the same means as type a) except for the fact the information is not located in the depth of the material used as coating (T) but because this coating is made up by materials (15), (16) and (17) in which the wave propagation speed is different.

This fact causes (when considering a constant propagation speed) the détections of boundaries (18), (19) and (20) to be distanced in a different manner from the détections of boundaries (20), (21) and (22).

J) Another information means we call type j) is the same as that defined as type e) except for the fact the information is not located in the thickness of the coating (8) but because this coating (24), and this coating is made up by materials in which the wave propagation speed is different, therefore considering a constant propagation speed there Is a différence between the détection of boundaries.

If we consider three blocks that are parallel to each other and perpendicular to the movement axis of the mobile, (85), (86) and (87) then the position différence between the upper boundaries of such blocks, (26), (27) and (28) and the corresponding lower ones (29), (30) and (31) causes the détection of the upper boundaries to be different from the détection of the lower boundaries according to the material used.

The dielectric change boundaries in a non-conductive materiai lead to part of the energy irradiated towards the materiai in question to be reflected.

This reflected energy is detected by the associated sensor making it possible to détermine the radial distance at which the discontinuity is found.

The dielectric change boundaries can be obtained by using two materials or substances whose dielectric constants are different or using a single materiai where the boundary is established between the materiai and the vacuum or the materiai or a gas or substance.

Having described sufficiently the nature of the invention, together with the way of putting it into practice, it should be stated that the provisions indicated above and represented in the attached drawings are susceptible to detailed modifications as long as they do not alter its basic prindples, established in the previous paragraphe and summarised in the following daims.

Claims

1. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure and characterised by the fact that along the trajectory described by a mobile it is possible to encode information in the infrastructure by means of different objects presenting dielectric change boundaries or dielectric/metal boundaries at different heights or distances regarding the origin of the onboard sensor, these boundaries being interrogated by a sensor on board the mobile by means of pressure or electromagnetic waves and by measuring the time the waves take to retum to the sensor, making it possible to determine the distance at which the reflections occur and in this way to extract the information.

2. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with claim 1 and characterised by the fact one information means regarding railway infrastructures refers to the information given by railway sleepers (T) as these present several singular characteristics:

- a uniform surface with regard to the ballast, or

- a different height regarding the track set on a concrète slab

3. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with claims 1 and 2 characterised by the fact the sleepers (T) are encoded with a sériés of bits by means of a variety of studs with

different heights.

The encoding of the sleeper (T) is performed by means of a variety of studs offering a sériés of levels in height (3), (4), (5) and (6) and these studs are covered with a material (2) permeable to the waves and of a known thickness.

The information on the position is divided into 4-bit groups which are encoded successively at each sleeper by means of the levels (3 and 4).

By altematively using the répétition level it is possible to identify consecutive 4-bit strings with the same logical level.

A fourth height level (6) is always used as the fifth bit for the sensor to be capable of knowing the reading direction.

4. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with the previous claims and characterised by the fact 4 bits of information obtain 24=16 different sleepers each encoding 5 bits (4 of information and 1 indicating the reading direction).

There is also a seventeenth sleeper model characteristic for its first bit starting with a répétition bit (5) and its fifth bit indicating the reading direction (6) which is used to indicate the start or end of a word made up by 4-bit groups.

The information is encoded redundantly in two different places for two sensors to be able to read the information means stmultaneously.

5. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position tn the infrastructure in accordance with the previous claims and charaderised by the fact the sensor interrogates the infrastructure with a spot 8mm in diameter and in order for each stud to be illuminated correctiy by the sensor, with the surface area of the studs being 1 cm2, the height séparation of each stud associated with a different logical level being 0.5 cm and these studs being covered with a material (2) permeable to waves of a known thickness.

6. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with claim 2 and characterised by the fact the sleeper (T) in which the information is encoded by slits instead of studs in such a way the sleeper shows no relief on its upper surface.

7. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with the previous daims and characterised by the fact the information means used consists in using the described stud or slit techniques on tracks set on a concrète slab.

8. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with daims 1 and 3 and charadensed by the fad the blocks encoded in accordance with the previous daims can be located on the sides or the upper part of the trajectory, and tumed round appropriately for their encoded part to face the sensor and arranged at a certain height in such a way there is direct view between the sensor and the block even under adverse weather conditions.

9. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with daim 1 and charactensed by the fact the means to be used on roads is made up by a sequence of specks/lines of a résistant material.

10. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into infonnation on rts exact position in the infrastructure in accordance with daims 1 and 9 and charactensed by the fad that when the specks/lines are the information means, these présent different thicknesses with 2 mm séparations between boundaries and are sfock longitudinally on the road in the centre/lane, each with a surface area of 1 cm2 and presenting an upper coating (8) of another permeable material with hydrophobie properties whtch serves as a reference point for the sensor.

11. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastrudure and allow for a mobile travelling along the same trajedory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exad position rn the infrastructure in accordance with daims 1, 9 and 10 and charaderised by the fad that when the specks/lines are the infonnation means, the information also being encoded by means of 3 different levels (9), (10) and (11) with 3 mm séparations and in 4bit groups plus a fifth bit (12) indicating the reading direction.

Between the 5-bit blocks, there is a free uncoded space and accompanying the sequence of specks, 2 side bands (13,14) of different thicknesses serve to encode the latéral drift of the sensor with regard to the information means where the information is encoded.

12. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform rt immediately into information on rts exact position in the infrastructure in accordance with daim 1 and charaderised by the fact another information means is made up by plastic strip with slits of different depths and with each centimètre encoded, in accordance with the levels defined in daim 3.

13. Encoded information means located on an infrastrudure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastrudure and allow for a mobile travelling along the same trajectory, provided with frie adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with daim 1 and characterised by the fact other information encoding means are made up by continuous or discontinuous objects of the same thickness and permeable to the waves with different transmission properties with regard to propagation speed, and in the case of electromagnetic waves, a different dielectric constant will delay more or less the détection assodated with the second dielectric change boundary due to the différence between the front and back surface of the object.

14. Encoded information means located on an infrastrudure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure and characterised by H).- Another way of encoding information we call type h), in accordance with figure 3 and consisting in the same means as type a) except for the fact the information is not located in the depth of the material used as coating (T) but because this coating is made up by materials (15), (16) and (17) in which the wave propagation speed is different

15. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with claims 13 and 14 and characterised by the /18 fact another information is made up by three biocks of material, parallel to each other and perpendicular to the movement axis of the mobile, (85), (86) and (87) where that occurring is that the différence in position between the upper boundaries of such biocks, (26), (27) and (28) and the corresponding lower ones (29), (30) and (31) causes the détection of the upper boundaries to be different from the détection of the lower boundaries and where the dielectric change boundaries can be obtained by using two materials or substances whose dielectric constants are different or using a single material where the boundary is established between the material and the vacuum or the material or a gas or another substance.

16. Encoded information means located on an infrastructure to be decoded by sensors located on mobiles, in such a way that these means encode the position they occupy in the infrastructure and allow for a mobile travelling along the same trajectory, provided with the adéquate sensor, to read, décodé and transform it immediately into information on its exact position in the infrastructure in accordance with daims 1 and 8 and characterised by the fact the surfaces of the boundaries can form trihedrons in order to maximize reftection.