WO2019157923A1

WO2019157923A1 - Environment mapping method and apparatus

Info

Publication number: WO2019157923A1
Application number: PCT/CN2019/072919
Authority: WO
Inventors: 任麒麟; 宋健; 江淑红; 熊春雷; 张小军
Original assignee: 视辰信息科技(上海)有限公司
Priority date: 2018-02-13
Filing date: 2019-01-24
Publication date: 2019-08-22
Also published as: CN108447086A; CN108447086B

Abstract

Disclosed is an environment mapping method, comprising the following steps: step one, dividing a sphere into three parts; step two, setting the size of a map; and step three, respectively mapping a lateral face part and a top face/a bottom face to a texture coordinate system by different texture coordinate mapping methods. According to the present invention, cylindrical projection which has higher fidelity and is simple in operation is used within an approximate vertical visual scope of human eyes, and due to the feature of conformal mapping of the cylindrical projection, better effects are obtained when scenes, such as a street scene, are observed. Regarding the treatment of southern and northern domes, in the present invention, the domes are uniformly mapped to rectangular maps as far as possible, and by adjusting the sizes of the rectangular maps of the southern and northern domes, joints between the southern and northern domes and an area near the equator can be removed, and the storage consumption of north and south poles can be reduced. By ensuring the continuity of mapping, the problem of pixel aggregation of the north and south poles in traditional cylindrical mapping is solved.

Description

Environment map mapping method and device

Technical field

Embodiments of the present invention relate to a computer graphics method, and in particular, to an environment map mapping method. Embodiments of the present invention also relate to an apparatus that uses an environment map mapping method.

Background technique

An environment map is an efficient way to simulate a scene around a viewpoint using pre-computed texture images in computer graphics rendering. The texture is used to store an image of the environment around the viewpoint, and the two-dimensional texture is mapped to the surface of the environment sphere in some way to simulate the environment image around the viewpoint. Environmental mapping has a wide range of applications: 360-degree streetscape rendering, indoor display, in-car environment display, and 360-degree VR video.

The existing environment mapping (Environment Mapping) methods are as follows:

Spherical Map: It is the simplest environment mapping method; given a sphere with a radius of 1, any point <x, y, z> on the surface of the sphere satisfies: x ² + y ² + z ² =1 Let p=sqrt(x ² +y ² +(z+1) ² ), then the texture coordinate of this point is (x/2p+0.5, y/2p+0.5). The advantage is simplicity, but the disadvantages are: stretching and distortion are noticeable, especially when z is close to zero, ie around the equator of the sphere. This is a fatal flaw in the display of environments such as Street View. In addition, the texture is not effectively utilized, and there is an invalid blank area.

Dual Paraboloid Environment Mapping: The double parabolic environment mapping is actually an improvement on spherical mapping. Double paraboloids are used to improve distortion and stretch at the edges and support 360-degree environmental mapping. The disadvantage is that there are still distortions and stretches; as with spherical mapping, there is also the problem of texture waste.

Cylindral Map: Given a sphere with a radius of 1, in the spherical coordinate system, θ and any point on the surface of the sphere can be used.

To represent. Where θ is called a polar angle and its value ranges from [0, π];

It is called azimuthal angle and its value ranges from [0, 2*π]. Any point on the sphere

Texture coordinates are

The advantage is that the cylindrical mapping is a kind of conformal mapping (so-called conformal mapping, that is, conformal mapping, which means that when one region is mapped to another region, the angle is kept constant), and it is protected within the visible range of the human eye. Highly true, suitable for showing environments such as Street View. The format is simple, the popularity is high, and many environment maps are provided in a cylindrical map. The disadvantage is that there are pixel aggregations at the north and south poles, and the storage space is more expensive.

Cube Map: Given a sphere with a radius of 1, first find the largest component according to any point <x, y, z> on the surface of the sphere, used to locate the external cube surface of the sphere, and then calculate on the plane. Out texture coordinates. The standard cube map is divided into six planes, the order of which is: X-axis positive direction, X-axis negative direction, Y-axis positive direction, Y-axis negative direction, Z-axis positive direction, Z-axis negative direction. The advantage is: relatively simple, the corresponding hardware implementation has been accelerated. The disadvantage is that the north and south poles, which are usually not of concern to the human eye, still use the same sampling rate as the side of the sphere.

IsoCube: The IsoCube mapping is actually a variant of the cube mapping. Unlike cube mapping, this technique attempts to map the sphere more evenly onto the cube. The advantage is that it is more uniform with respect to the cube mapping. The disadvantage is that there is a non-conformal mapping and there is a pixel distortion problem. The north and south poles, which are usually not of concern to the human eye, still use the same sampling rate as the side of the sphere. In addition, due to its low penetration rate, re-sampling of existing environmental maps is required, which will result in a decrease in texture accuracy.

HEALPix mapping, HEALPix mapping is called Hierarchical Equal Area isoLatitudePixelization. The method first divides the sphere into 12 quadrilateral blocks of the same area, and then recursively subdivides the block into smaller quadrilateral blocks. However, anti-aliasing for the HEALPix mapping method requires a special algorithm, which makes the mapping operation more complicated. The advantage is that the entire sphere achieves uniform mapping, uniform area, and small distortion. The disadvantage is that the operation is more complicated. For the 360-degree street view, the use of the North and South poles is not high, and the North and South poles are not optimized.

In summary, when a static scene is displayed using a 360-degree environmental ball, the above-described environment mapping method cannot satisfactorily meet the requirements of low storage space consumption and high image quality. Spherical Map and its improved method Dual Paraboloid Environment Mapping has the problem of texture waste and pixel distortion and aggregation at the mapping boundary; Cylindrical Map based on latitude and longitude can be seen in the human eye. The effect is better in the range, but there is a problem of pixel aggregation and a large amount of storage space being wasted at the north and south poles; Cube Map, IsoCube, and HEALPix map waste more storage space for Store non-interest areas, that is, pixels of the north and south poles of the environment ball.

Summary of the invention

In order to solve the above technical problem, the present invention provides a partially conformal environment map mapping method, which can use less data amount to achieve an approximately equal effect in the visible range of the human eye, and simultaneously solve the cylindrical mapping in the north and south. The problem of pixel aggregation of the two poles.

The technical solution of the partially conformal environment map mapping method proposed by the present invention comprises the following steps:

The first step is to divide the environmental sphere into three parts:

Side portion: θ takes a spherical portion of [π/2-A ₁ , π/2+A ₂ ];

Top surface: the spherical top dome portion of θ ranging from [0, π/2–A ₁ );

Bottom surface: the spherical bottom portion of the sphere with a range of θ (π/2+A ₂ , π);

Where θ is the angle between the direction vector of any point on the surface of the sphere in the spherical coordinate system and the Z axis; the spherical coordinate system refers to a sphere with a radius of 1, in the spherical coordinate system, any point on the surface of the sphere Angle θ and azimuth

To show that θ has a value range of [0, π],

The value range is [0, 2π];

The angle A _{1 has} a value range of 0 < A ₁ <π/2;

The angle A _{2 has} a value range of 0 < A ₂ <π/2;

Preferably, in the first step, the values of A ₁ and A ₂ are π/6 ≤ A ₁ ≤ π / 3, and the test results show that the best values of A ₁ and A ₂ in the first step are π/4.

In the second step, set the size of the texture to:

Let the texture width corresponding to the side part be N, and the value of N be a power of 2; then the texture size corresponding to each part is:

Side portion: the texture width is N, and the height is S ₁ × N × ((A ₁ + A ₂ ) / (2π));

Wherein S ₁ is a scaling factor;

Top/bottom part: the width of the texture is S ₂ ×N/4, and the height is S ₃ ×N/4;

Among them, S ₂ and S ₃ are both scaling factors.

Preferably, the values of S ₁ , S ₂ , and S ₃ are 1, and the width and height of the top cover and the bottom cover portion are N/4, and the width of the side portion map is N.

In the third step, the side portion and the top surface/bottom surface are mapped to the texture coordinate system by using different texture coordinate mappings, wherein the texture coordinate system refers to the horizontal direction of the texture as the u-axis and the vertical direction as the v-axis. The coordinates of the four corners are respectively (0, 0), (1, 0), (0, 1), (1, 1) coordinate system, and the side portion and the top/bottom dome are mapped. The shape matches the size of the texture.

Further, the texture coordinates of the side portion in the third step are:

v=(θ-A ₁ )/(A ₁ +A ₂ );

among them,

Projecting a direction vector of any point on the surface of the sphere in the spherical coordinate system to the angle between the XY plane and the X axis;

u is the coordinate value of the horizontal direction in the texture coordinate system;

v is the coordinate value of the vertical direction in the texture coordinate system.

Further, the texture coordinate mapping method of the top/bottom portion in the third step is:

The top/bottom dome is evenly divided, and each block is mapped to a part of the rectangle.

Further, the top/bottom dome is evenly divided into 4 parts, each of which is mapped to a corresponding position of the rectangle;

Define the shortest spherical arc distance from any point on the dome to the center of the dome as D, and let L be the value that normalizes D to [0,0.5], then the L value at any point on the top cover Is: 0.5 × θ / (π / 2 - A ₁ ), and the L value of any point on the bottom dome is: 0.5 × (π - θ) / (π / 2 - A ₂ );

definition

For the

The range of values is mapped to the value of [-π/4,7×π/4), which is:

(when

Time)

(when

Time)

The texture coordinates of the top/bottom dome are divided into the following four cases, corresponding to four areas:

The first,

v=0.5+L

Second,

u=0.5+L

Third,

v=0.5-L

Fourth,

u=0.5–L

among them,

The invention also provides an apparatus using an environment map mapping method, and the technical solution thereof is:

A processor is included for performing the method steps described above.

The technical effects that can be achieved by the present invention are:

The vertical viewing range of the human eye is about 100 degrees. The present invention adopts a cylindrical projection with high fidelity and simple operation in the vertical visible range close to the human eye. Due to the characteristics of the conformal mapping, the street view is observed. Get better results when you wait for the scene. In addition, since a large number of existing environmental mapping maps exist in the form of cylindrical projections, the present invention can ensure that there is no need to perform texture resampling within the visible range of the human eye for these existing textures, so that precision loss does not occur.

In the treatment of the two round covers of the north and the south, the present invention maps the round cover as evenly as possible onto the rectangular map, and by adjusting the size of the north-south round-shaped rectangular map, the joint between the north-south round cover and the area near the equator can be eliminated. And reduce the storage consumption of the north and south poles. By ensuring the continuity of the mapping, the pixel aggregation problem of the two poles in the traditional cylindrical mapping is eliminated. Optimally, when the above parameters A ₁ and A ₂ take a value of π/4 and S ₁ , S ₂ and S ₃ both take 1, the texture of the entire sphere just surrounds the seamless connection, and only the cylindrical mapping is used 75%. The amount of data.

DRAWINGS

Those skilled in the art should understand that the following description is merely illustrative of the principles of the invention, which can be applied in various ways to implement many different alternative embodiments. The illustrations are only intended to illustrate the general principles of the teachings of the present invention and are not intended to limit the inventive concepts disclosed herein.

The accompanying drawings, which are incorporated in the claims

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

Figure 1 is a schematic illustration of a spherical coordinate system used in an embodiment of the present invention;

2 is a schematic diagram of a texture coordinate system used in an embodiment of the present invention;

3 is a schematic diagram of a method for mapping texture coordinates according to an embodiment of the present invention;

Figure 4 is a schematic view of a texture used in the prior art;

Figure 5 is a schematic view of a texture used in an embodiment of the present invention;

FIG. 6 is a schematic diagram of an image processing apparatus using an environment map mapping method according to an embodiment of the present invention.

Detailed ways

The technical solutions of the embodiments of the present invention will be clearly and completely described in the following with reference to the accompanying drawings. It is apparent that the described embodiments are part of the embodiments of the invention, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the described embodiments of the present invention without departing from the scope of the invention are within the scope of the invention. Unless otherwise defined, technical terms or scientific terms used herein shall be taken to mean the ordinary meaning of the ordinary skill in the art to which the invention pertains. The use of the terms "comprises" or "an" or "an" or "an"

The coordinate system used in this paper is defined as follows:

Spherical coordinate system: Given a sphere with a radius of 1, in the spherical coordinate system, θ and any point on the surface of the sphere can be used.

To indicate; where θ is called the polar angle, and its value ranges from [0, π];

It is called azimuthal angle and its value ranges from [0, 2π].

FIG. 1 is a spherical coordinate system used in an embodiment of the present invention, where r=1,

The spherical direction vector is projected to the angle between the XY plane and the X axis, and the value ranges from [0, 2π]. θ is the angle between the spherical direction vector and the Z axis, and the value ranges from [0, π].

Texture coordinate system: The horizontal direction of the image is the u-axis, and the vertical direction is the v-axis. The coordinates corresponding to the four corners of the image are shown in Figure 2.

The coordinate system in this article is for convenience only. Even if other coordinate systems are used, the effects achieved by the embodiments of the present invention can be achieved by the conversion of the coordinate system.

Embodiment 1:

An embodiment of the present invention provides an environment map mapping method, including the following steps:

In the first step (S1), the environmental sphere sphere is divided into three parts:

Side portion: θ takes a spherical portion of [π/2-A ₁ , π/2+A ₂ ];

Bottom surface: θ takes the range of (π / 2 + A ₂ , π) spherical bottom cover portion;

Wherein, the angle A _{1 has} a value range of 0<A ₁ <π/2;

The angle A _{2 has} a value range of 0 < A ₂ <π/2;

Preferably, the values of A ₁ and A ₂ may be π/6 ≤ A ₁ ≤ π / 3, and the test results show that the optimal values of A ₁ and A ₂ are π/4.

In the second step (S2), the size of the map is set and the side portion and the top surface/bottom surface are respectively mapped to the texture coordinate system by using different texture coordinate mappings, wherein the texture coordinate system refers to the horizontal direction of the texture as the u-axis. The vertical direction is the v-axis, and the coordinates of the four corners of the map are coordinate systems of (0, 0), (1, 0), (0, 1), (1, 1), respectively, the side portion and the The shape of the top/bottom dome is mapped to match the size of the texture.

Let the texture width corresponding to the side part be N, and the value of N is generally a power of 2; then the texture size of each part and the texture coordinates on the texture are:

Wherein, S ₁ is a scaling factor, and an optimal value of S ₁ is 1;

v=(θ-A ₁ )/(A ₁ +A ₂ );

Where S ₂ and S ₃ are both scaling factors, and the optimal values of S ₂ and S ₃ are 1.

When S ₁ , S ₂ and S ₃ are both taken 1, the width and height of the top and bottom dome portions are N/4, and the width of the side portion map is N. At this time, the entire sphere is divided into three parts. The textures just fit seamlessly around the border.

When both A ₁ and A ₂ take the value π/4 and S ₁ , S ₂ and S ₃ both take 1, the texture of the entire sphere just surrounds the seamless connection, and only the cylindrical mapping is used for 75% of the data amount.

The mapping method of the top/bottom dome is as shown in FIG. 3, and the top/bottom dome is evenly divided into 4 parts, and each part is mapped to a corresponding position of the rectangle;

definition

For the

The range of values is mapped to the value of [-π/4,7×π/4), which is:

(when

Time)

(when

Time)

Then the texture coordinates of the top/bottom dome can be divided into the following four cases, corresponding to the four regions in Figure 3:

The first,

v=0.5+L

Second,

u=0.5+L

Third,

v=0.5-L

Fourth,

u=0.5–L

The above is the texture coordinate mapping formula.

In the embodiment of the present invention, since the vertical visible range of the human eye is about 100 degrees, a cylindrical projection with high fidelity and simple operation is adopted in the vertical visible range close to the human eye, due to its conformal mapping. Features, so that you can get better results when viewing scenes such as street scenes. In addition, since a large number of existing environmental mapping maps exist in the form of cylindrical projections, the present invention can ensure that there is no need to perform texture resampling within the visible range of the human eye for these existing textures, so that precision loss does not occur.

Embodiment 2:

An embodiment of the present invention further provides a preferred environment map mapping method, including the following steps:

S1, the sphere is divided into three parts, of which:

Side portion: any value between 0 degrees and 90 degrees on the upper and lower sides of the equator of the sphere (the optimum value is 45 degrees), respectively, the surface is cut in the horizontal direction, and the cylindrical projection is used for the curved surface;

Top surface: the southern dome that remains after cutting the sphere;

Bottom surface: the northern dome that remains after cutting the sphere;

Set the dimensions of the map and the coordinates of the map in the texture coordinate system, where:

S11. In this embodiment, the size of the texture may be 1024 pixels×512 pixels, the upper part displays the mapping result of the top surface of the sphere, the middle part displays the mapping result of the side of the sphere, and the lower part shows the mapping result of the bottom surface of the sphere. Half part: middle part: lower part = 1: 2:1;

S12, the horizontal direction of the texture is the u axis, and the vertical direction is the v axis, and the coordinates of the four corners of the texture are defined as (0, 0), (1, 0), (0, 1), (1, 1), respectively. To construct the texture coordinate system of the texture;

S2, the side portion and the top surface/bottom surface are mapped to the texture coordinate system by different texture coordinate mapping manners, the side portions of the sphere are cylindrically mapped, and the mapping result is displayed in the middle portion of the texture; the top surface and the bottom surface are performed. The texture coordinate map displays the mapping results in the upper and lower parts of the remaining textures.

After mapping the mapping results of the side part, the top surface and the bottom surface to the texture map, the three parts can be completely spliced together, which enhances the visual experience.

Embodiment 3:

The environment map mapping method provided by the embodiment of the present invention can be applied to the scene of the AR/VR car. The following describes the technical solution of the present invention by using an AR/VR car display as an embodiment:

In the AR/VR car show, there is a scene that needs to simulate the user's point of view to simulate the real in-car viewpoint. You can look around and check the interior decoration, including the seat, the dashboard, etc. You can see it in the car. In-car equipment; such display in the 3D engine is generally achieved by using a panorama attached to the inner wall of a hollow sphere, the position of the camera is fixed to the center of the ball, you can see the effect close to the real car, in this implementation In the example, a hollow sphere with a radius of 5 meters is constructed; the panorama can be acquired in many ways, usually by a special camera. The prior art usually uses the original interior map as shown in Figure 4. It is also a map that can be used directly by a spherical map.

The spherical mapping map shown in FIG. 4 is divided into three parts. The area of 512×64 pixels from the top of the texture is the part showing the sunroof in the car, and the area of 512×128 pixels in the middle is the part showing the head-view range. The 512×64 pixel area at the bottom of the texture is the part that shows the bottom of the car; if you use this texture by sphere mapping on the sphere in this scene, you can find that the north and south poles of the texture use a lot of pixels, but the spherical map At that time, it will only correspond to very few pixels, which is a great waste; the texture area of this method is 512 × 256 = 131072 in total;

Most of the time the user observes is sitting in the car's flat view, and can look around for a week; for the roof and the bottom of the car, the observation is much less. Therefore, the method of the invention can be employed:

Divide the original cylindrical map into three parts: top, middle, and bottom, where the top and bottom textures are the same size;

Set the size of the texture to 512 × 256, using the optimal parameters, that is, both A ₁ and A ₂ take the value π / 4 and S ₁ , S ₂ and S ₃ take 1 to map the three parts of the hollow sphere separately:

The side part adopts a cylindrical map and maps to the map area showing the head-view range. The size of the side part is 512×128; the side part is a map showing the head-view range, which is the same as the map size and content of the spherical map;

The top surface adopts texture mapping, and each point of the top surface is mapped to texture coordinates, and the size of the top surface portion after mapping is 128×128; the top surface portion is used as a map for displaying the sunroof inside the vehicle;

The bottom surface also adopts texture mapping, and each point of the bottom surface is mapped to texture coordinates, and the size of the bottom portion is mapped to 128×128; the bottom portion is used as a map showing the bottom of the vehicle;

After the hollow sphere is mapped to the texture area, the seamless connection and display of the image is completed, as shown in FIG. 5.

After the method provided by the embodiment of the present invention, the mapped area of the hollow sphere is 128×128+128×128+512×128=98304; therefore, compared with the spherical map, the method provided by the embodiment of the present invention is adopted. The compression ratio of the texture area can reach 98304/131072=75%.

Embodiment 4:

As shown in FIG. 6, the apparatus for using the environment map mapping method provided by the embodiment of the present invention further includes a memory 41 and a processor 42, wherein the memory 41 is configured to store code and related data, and the processor 42 is configured to call the memory 41. The data in the memory 41 is executed, and the code in the memory 41 is executed to implement the environment map mapping method provided in the first embodiment and the second embodiment. The specific method steps refer to the description of the foregoing embodiment, and details are not described herein again. .

In the embodiment of the present invention, the memory 41 may include a volatile memory, such as a random access memory (RAM), and the RAM may include a static RAM or a dynamic RAM. The memory 41 may also include a non-volatile memory such as a read-only memory (PROM), a programmable read-only memory (PROM), and a rewritable memory. An erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM) or a flash memory. The memory 41 may also be an external flash memory, at least one disk storage or a buffer.

In the embodiment of the present invention, the processor 42 may be a central processing unit (CPU), and the processor 42 may also be other general-purpose control processors, digital signal processing (DSP), and application specific integrated circuits. (Application Specific Integrated Circuit, ASIC), Field-Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, etc. The general purpose control processor may be a micro control processor or any conventional control processor such as a microcontroller or the like.

In the several embodiments provided by the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the device embodiments described above are merely illustrative. For example, the division of the modules or units is only a logical function division. In actual implementation, there may be another division manner, for example, multiple units or components may be used. Combinations can be integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interface, device or unit, and may be in an electrical, mechanical or other form.

The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

It can be understood by those skilled in the art that all or part of the steps of implementing the above method embodiments may be completed by hardware related to the program instructions, and the foregoing programs may be stored in a computer readable storage medium and processed by the communication device. The processor executes, and the aforementioned program, when executed, can execute all or part of the steps including the above method embodiments. The processor may be implemented as one or more processor chips, or may be part of one or more application specific integrated circuits (ASICs); and the foregoing storage medium may include but not be limited to the following types. Storage medium: flash memory, read-only memory (ROM), random access memory (RAM), mobile hard disk, disk or optical disk, etc. .

The invention adopts a cylindrical mapping of the vicinity of the equator of the sphere, and maps the north and south poles of the sphere to the rectangle, which has high fidelity in the visible range of the human eye, and solves the problem of pixel aggregation of the cylindrical mapping at the north and south poles. It also reduces storage consumption.

It is apparent that those skilled in the art can make various modifications and variations to the invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and the modifications

Claims

An environment map mapping method, comprising the steps of:

The first step is to divide the environmental sphere into three parts:

Side portion: θ takes a spherical portion of [π/2-A 1 , π/2+A 2 ];

Top surface: the spherical top dome portion of θ ranging from [0, π/2–A 1 );

Bottom surface: θ takes the range of (π / 2 + A 2 , π) spherical bottom cover portion;

Where θ is the angle between the direction vector of any point on the surface of the sphere in the spherical coordinate system and the Z axis; the spherical coordinate system refers to a sphere with a radius of 1, in the spherical coordinate system, any point on the surface of the sphere The angle θ and the azimuth angle φ indicate that the value range of θ is [0, π], and the value range of φ is [0, 2π];

The angle A 1 has a value range of 0 < A 1 <π/2;

The angle A 2 has a value range of 0 < A 2 <π/2;

The second step is to set the size of the texture;

In the third step, the side portion and the top surface/bottom surface are respectively mapped to the texture coordinate system by using different texture coordinate mappings, wherein the texture coordinate system refers to the horizontal direction of the texture as the u-axis and the vertical direction as the v-axis, and the texture The coordinates of the four corners are respectively (0, 0), (1, 0), (0, 1), (1, 1) coordinate system, and the side portion and the top/bottom dome are mapped. The shape matches the size of the texture.
The environment map mapping method according to claim 1, wherein the values of A 1 and/or A 2 in the first step are:

The angle A 1 has a value range of π/6 ≤ A 1 ≤ π / 3;

The angle A 2 has a value range of π/6 ≤ A 1 ≤ π / 3.
The environment map mapping method according to claim 2, wherein A 1 and/or A 2 of the first step have a value of π/4.
The environment map mapping method according to claim 1, wherein the size of the map set in the second step is:

If the texture width corresponding to the side part is N, the corresponding map size of each part is:

Side portion: the texture width is N, and the height is S 1 × N × ((A 1 + A 2 ) / (2π));

Wherein S 1 is a scaling factor;

Top/bottom part: the width of the texture is S 2 ×N/4, and the height is S 3 ×N/4;

Among them, S 2 and S 3 are both scaling factors.
The environment map mapping method according to claim 4, wherein the value of N is a power of two.
The environment map mapping method according to claim 4, wherein the values of S 1 , S 2 , and S 3 are 1, and the width and height of the top cover and the bottom cover portion are N/4. The width of the side part map is N.
The environment map mapping method according to claim 4, wherein the texture coordinates of the side portion of the third step are:

v=(θ-A 1 )/(A 1 +A 2 );

among them,
Projecting a direction vector of any point on the surface of the sphere in the spherical coordinate system to the angle between the XY plane and the X axis;

u is the coordinate value of the horizontal direction in the texture coordinate system;

v is the coordinate value of the vertical direction in the texture coordinate system.
The environment map mapping method according to claim 1, wherein the texture coordinate mapping method of the top/bottom portion in the third step is:

The top/bottom dome is evenly divided, and each block is mapped to a part of the rectangle.
The environment map mapping method according to claim 1 or 8, wherein

The top/bottom dome is evenly divided into 4 parts, each of which is mapped to a corresponding position of the rectangle;

Define the shortest spherical arc distance from any point on the dome to the center of the dome as D, and let L be the value that normalizes D to [0,0.5], then the L value at any point on the top cover Is: 0.5 × θ / (π / 2 - A 1 ), and the L value of any point on the bottom dome is: 0.5 × (π - θ) / (π / 2 - A 2 );

definition
For the
The range of values is mapped to the value of [-π/4,7×π/4), which is:

(when
Time)

(when
Time)

The texture coordinates of the top/bottom dome are divided into the following four cases, corresponding to four areas:

The first,

v=0.5+L

Second,

u=0.5+L

Third,

v=0.5-L

Fourth,

u=0.5–L

among them,
Projecting a direction vector of any point on the surface of the sphere in the spherical coordinate system to the angle between the XY plane and the X axis;

u is the coordinate value of the horizontal direction in the texture coordinate system;

v is the coordinate value of the vertical direction in the texture coordinate system.
An apparatus for employing an environment map mapping method, comprising: a processor for performing the method steps of any one of claims 1 to 9.