CN111951370A - Direct volume rendering method for data acquired by rotational scanning - Google Patents
Direct volume rendering method for data acquired by rotational scanning Download PDFInfo
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- CN111951370A CN111951370A CN202010812141.9A CN202010812141A CN111951370A CN 111951370 A CN111951370 A CN 111951370A CN 202010812141 A CN202010812141 A CN 202010812141A CN 111951370 A CN111951370 A CN 111951370A
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- 238000000034 method Methods 0.000 title claims abstract description 21
- 238000009877 rendering Methods 0.000 title claims abstract description 18
- 238000005070 sampling Methods 0.000 claims abstract description 89
- 239000003086 colorant Substances 0.000 claims abstract description 18
- 230000005540 biological transmission Effects 0.000 claims description 6
- 238000009825 accumulation Methods 0.000 claims description 3
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 238000000605 extraction Methods 0.000 claims description 3
- 230000010354 integration Effects 0.000 claims description 2
- 238000001514 detection method Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 238000013079 data visualisation Methods 0.000 description 1
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- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T15/00—3D [Three Dimensional] image rendering
- G06T15/08—Volume rendering
Abstract
A direct volume rendering method facing to rotation scanning collected data includes drawing proxy cylinder according to size of rotation scanning collected data being volume data, leading out ray to surface of proxy cylinder according to viewpoint, sampling on all rays, converting column coordinate of sampling point to texture coordinate, obtaining pixel value of corresponding coordinate according to texture sampling function, finding out corresponding color in color code table according to pixel value of sampling point, mixing colors of sampling point on one ray, using mixed color as pixel color value, outputting all pixels to obtain volume rendering image The sampling process is time-consuming, the accuracy of data is improved, and the sampling time is reduced.
Description
Technical Field
The invention relates to a direct volume rendering method for rotational scanning acquired data, and belongs to the technical field of three-dimensional data visualization.
Background
In many industrial fields, a rotary scanning mode is used for acquiring volume data of real entities, and the data acquired by the acquisition mode is closer to an actually scanned object. The rotary scanning is to transmit detection signals to a real entity through a scanning antenna on the side surface of a scanner and receive echo signals; and the side surface of the scanner is also provided with a scanning trigger which moves synchronously with the scanning antenna and is used for recording the movement distance of the scanning antenna, and when the movement distance reaches the preset movement distance, the scanning trigger triggers the signal transceiver circuit once, so that the signal transceiver circuit controls the scanning antenna to transmit detection signals to the detected object and outputs all the detection signals to acquire the body data of the real entity. The volume data is a description of a data type, and may be called volume data as long as it contains internal details, and the volume data generated by the rotational scanning method is a type of volume data stored based on cylindrical coordinates.
At present, in the existing volume rendering, a regular cube is used as a proxy geometric body in a three-dimensional rectangular coordinate, a ray is emitted from a viewpoint along a fixed direction, data sampling is carried out according to the sampling position of the ray in the cube, and finally, a corresponding color value is found from a color code table according to a sampled superposition value and is used as a color value of one pixel on the surface of the cube for display and output.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a direct volume rendering method for rotational scanning acquired data, which can directly render the rotational scanning acquired volume data and has the advantages of high calculation speed and high sampling precision.
The technical scheme for realizing the aim of the invention is that the direct volume rendering method facing the data acquired by the rotational scanning at least comprises the following steps:
(1) drawing a proxy cylinder according to the size of the rotary scanning acquired data, namely the volume data;
(2) respectively leading out rays from a viewpoint to different points on the surface of the proxy cylinder, sampling on all the rays with a fixed step length to obtain sampling points, wherein the sampling points are data points on a column coordinate, specifically, sampling on the rays with the viewpoint as a starting point with the fixed step length to obtain the sampling points, continuously sampling the newly obtained sampling points on the rays with the fixed step length as the starting point to obtain sub-sampling points, repeating the sampling steps, namely, the light passes through the whole cylinder to obtain N sampling points, and only selecting the sampling points in the proxy cylinder;
(3) and converting the cylindrical coordinates of the obtained sampling points into texture coordinates, and acquiring pixel values of corresponding coordinates according to a texture sampling function, wherein the texture coordinate conversion formula is as follows:
s ═ phi + pi)/(2 pi) formula 1
P/rad equation 2
r-z/h equation 3
In the formula, s, t and r are coordinate values of three dimensions of texture, phi is an azimuth angle value in a column coordinate, rho is a radius value in the column coordinate, rad is the radius of the proxy cylinder, and h is the height of the proxy cylinder;
(4) finding out corresponding colors in a color code table according to pixel values of sampling points, mixing the colors of the selected sampling points on one ray according to a light transmission formula from back to front, and taking the mixed colors as pixel color values of ray extraction points on the surface of the proxy cylinder;
(5) and (5) repeating the step (4), and outputting all pixels after obtaining the pixel color values of all points on the surface of the proxy cylinder to obtain the volume rendering image.
The technical scheme is further improved in that the data values of the sampling points in the step (2) are obtained by the following formula:
Z-Z equation 6
In the formula 4, x and y are data values of a horizontal axis and a longitudinal axis of the sampling point in a three-dimensional rectangular coordinate respectively, and rho is a radius value in a column coordinate; in the formula 5, x and y are data values of a horizontal axis and a vertical axis of the sampling point in a three-dimensional rectangular coordinate respectively, and phi is an azimuth angle value in a column coordinate; in the formula 6, Z is a vertical axis data value of a sampling point in a three-dimensional rectangular coordinate, and Z is a height coordinate value in a column coordinate;
and the step length in the step (2) is obtained by the following formula:
D＝V÷S
in the formula, D is the step length, V is the diameter of the proxy cylinder surrounding ball, and S is the maximum sampling step number.
And the light transmission formula in the step (4) is as follows:
in the formula, CiFor sampling the resulting color values, AiOpacity for sampling;
the color value obtained after the accumulation;
opacity of color values obtained after integration.
Known from the above technical solutions, the method for direct volume rendering oriented to the rotational scanning acquired data provided by the present invention draws a proxy cylinder according to the size of the rotational scanning acquired data, i.e. the volume data, then draws rays from a viewpoint to the surface of the proxy cylinder, and samples all the rays with a fixed step length to obtain sampling points, converts the cylindrical coordinates of the sampling points into texture coordinates, obtains the pixel values of the corresponding coordinates according to a texture sampling function, finds the corresponding colors in a color code table according to the pixel values of the sampling points, mixes the colors of the selected sampling points on one ray in a back-to-front manner, uses the mixed colors as the pixel color values of the ray-drawn points on the surface of the proxy cylinder, outputs all the pixels after obtaining the pixel color values of all the points on the surface of the proxy cylinder, and obtains the result image, according to the method, the proxy cylinder is drawn according to the size of the volume data, then rays are taken on the proxy cylinder and sampling is carried out, the data of the cylindrical coordinates can be directly processed, the problems that the volume data which are generated by a rotary scanning method and stored based on the cylindrical coordinates need to be resampled into the volume data under the three-dimensional rectangular coordinates by a volume drawing technology, the generated data can lack accuracy, and the sampling process is time-consuming are solved, the accuracy of the data is improved, and the sampling time is shortened.
Drawings
FIG. 1 is a projection diagram of a conventional volume rendering method according to the present invention;
fig. 2 is a projection diagram of the direct volume rendering method for rotational scan data acquisition according to the present invention.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and examples.
Referring to fig. 1 to 2, acquiring rotational scanning acquired data and drawing a proxy cylinder according to the size of the rotational scanning acquired data, i.e., volume data;
the volume data is three-dimensional grid field data, each grid point corresponds to a data value and is stored as a binary file;
respectively leading out rays from a viewpoint to different points on the surface of the proxy cylinder, sampling on all the rays with a fixed step length to obtain sampling points, wherein the sampling points are data points on a column coordinate, specifically, sampling on the rays with the viewpoint as a starting point with the fixed step length to obtain the sampling points, continuously sampling the newly obtained sampling points with the newly obtained sampling points as the starting point on the rays with the fixed step length to obtain sub-sampling points, repeating the sampling steps, namely, the light passes through the whole cylinder to obtain N sampling points, N is more than or equal to 1, and only selecting the sampling points in the proxy cylinder;
the data values of the sampling points in this embodiment are obtained by the following formula:
Z-Z equation 3
In the formula 1, x and y are data values of a horizontal axis and a longitudinal axis of a sampling point in a three-dimensional rectangular coordinate respectively, and rho is a radius value in a column coordinate; in the formula 2, x and y are data values of a horizontal axis and a vertical axis of the sampling point in a three-dimensional rectangular coordinate respectively, and phi is an azimuth angle value in a column coordinate; in the formula 3, Z is a vertical axis data value of a sampling point in a three-dimensional rectangular coordinate, and Z is a height coordinate value in a column coordinate; the step size in this embodiment is obtained by the following formula:
D＝V÷S
in the formula, D is the step length, V is the diameter of the proxy cylinder surrounding ball, and S is the maximum sampling step number.
Converting the cylindrical coordinates of the obtained sampling points into texture coordinates again, and then obtaining pixel values of corresponding coordinates according to a texture sampling function, specifically obtaining the pixel values of the corresponding coordinates through the texture sampling function in a shader, wherein the texture coordinate conversion formula is as follows:
s ═ phi + pi)/(2 pi) equation 4
P/rad equation 5
r-z/h equation 6
In the formula, s, t and r are coordinate values of three dimensions of texture, phi is an azimuth angle value in a column coordinate, rho is a radius value in the column coordinate, rad is the radius of the proxy cylinder, and h is the height of the proxy cylinder;
then finding out corresponding colors in a color code table according to pixel values of sampling points, mixing the colors of the selected sampling points on one ray according to a light transmission formula from back to front, and taking the mixed colors as pixel color values of ray extraction points on the surface of the proxy cylinder;
the color code table, i.e., RGB color scheme, is a color standard in the industry, which obtains various colors by changing three color channels of red (R), green (G), and blue (B) and superimposing them with each other, where RGB represents the colors of the three channels of red, green, and blue, and this standard almost includes all colors that can be perceived by human vision, and is one of the most widely used color systems at present.
The RGB color mode uses an RGB model to assign an intensity value in the range of 0-255 to the RGB components of each pixel in the image. The RGB image uses only three colors, which can be mixed in different proportions to reproduce 16777216(256 by 256) colors on the screen.
And finally, repeating the steps, and outputting all pixels after obtaining the pixel color values of all points on the surface of the proxy cylinder to obtain a volume rendering image. Wherein the light transmission formula is shown below:
in the formula, CiFor sampling the resulting color values, AiOpacity for sampling;
the color value obtained after the accumulation;
accumulationAnd the color value opacity obtained thereafter.
According to the method, the proxy cylinder is drawn according to the size of the volume data, then rays are taken on the proxy cylinder and sampling is carried out, the data of the cylindrical coordinates can be directly processed, the problems that the volume data which are generated by a rotary scanning method and stored based on the cylindrical coordinates need to be resampled into the volume data under the three-dimensional rectangular coordinates by a volume drawing technology, the generated data can lack accuracy, and the sampling process is time-consuming are solved, the accuracy of the data is improved, and the sampling time is shortened.
Claims (4)
1. A direct volume rendering method for rotational scan acquired data, comprising at least the steps of:
(1) drawing a proxy cylinder according to the size of the rotary scanning acquired data, namely the volume data;
(2) respectively leading out rays from a viewpoint to different points on the surface of the proxy cylinder, sampling on all the rays with a fixed step length to obtain sampling points, wherein the sampling points are data points on a column coordinate, specifically, sampling on the rays with the viewpoint as a starting point with the fixed step length to obtain the sampling points, continuously sampling the newly obtained sampling points on the rays with the fixed step length as the starting point to obtain sub-sampling points, repeating the sampling steps, namely, the light passes through the whole cylinder to obtain N sampling points, and only selecting the sampling points in the proxy cylinder;
(3) and converting the cylindrical coordinates of the obtained sampling points into texture coordinates, and acquiring pixel values of corresponding coordinates according to a texture sampling function, wherein the texture coordinate conversion formula is as follows:
s ═ phi + pi)/(2 pi) formula 1
P/rad equation 2
r-z/h equation 3
In the formula, s, t and r are coordinate values of three dimensions of texture, phi is an azimuth angle value in a column coordinate, rho is a radius value in the column coordinate, rad is the radius of the proxy cylinder, and h is the height of the proxy cylinder;
(4) finding out corresponding colors in a color code table according to pixel values of sampling points, mixing the colors of the selected sampling points on one ray according to a light transmission formula from back to front, and taking the mixed colors as pixel color values of ray extraction points on the surface of the proxy cylinder;
(5) and (5) repeating the step (4), and outputting all pixels after obtaining the pixel color values of all points on the surface of the proxy cylinder to obtain the volume rendering image.
2. The direct volume rendering method facing rotational scan acquisition data as claimed in claim 1, wherein the data values of the sampling points in step (2) are obtained by the following formula:
Z-Z equation 6
In the formula 4, x and y are data values of a horizontal axis and a longitudinal axis of the sampling point in a three-dimensional rectangular coordinate respectively, and rho is a radius value in a column coordinate; in the formula 5, x and y are data values of a horizontal axis and a vertical axis of the sampling point in a three-dimensional rectangular coordinate respectively, and phi is an azimuth angle value in a column coordinate; in the formula 6, Z is a vertical axis data value of the sampling point in a three-dimensional rectangular coordinate, and Z is a height coordinate value in a column coordinate.
3. The method for direct volume rendering oriented to rotational scan acquisition data as claimed in claim 1, wherein the step size in step (2) is obtained by the following formula:
D＝V÷S
in the formula, D is the step length, V is the diameter of the proxy cylinder surrounding ball, and S is the maximum sampling step number.
4. The method of direct volume rendering oriented to rotational scan acquisition data of claim 1, wherein the light transmission formula in step (4) is as follows:
in the formula, CiFor sampling the resulting color values, AiOpacity for sampling;
the color value obtained after the accumulation;
opacity of color values obtained after integration.
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| CN113077539A (en) * | 2021-04-08 | 2021-07-06 | 网易（杭州）网络有限公司 | Target virtual model rendering method and device and electronic equipment |
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Application publication date: 20201117 |