CN117474749A - 2.5-dimensional map projection method - Google Patents

Abstract

The invention discloses a 2.5-dimensional map projection method, which belongs to the technical field of image processing, wherein DOM raster data, DEM raster data and DLG vector data of original map data are obtained, and the obtained DOM raster data, DEM raster data and DLG vector data are subjected to data preprocessing to obtain original map block grids; establishing a target map projection plane coordinate system; performing projection conversion on the obtained original image block grids to obtain corresponding block target map grids, and performing transverse splicing to form projected target map grid data of the DOM full map; for DLG vector data, three geometric element types of the point, the line and the plane are respectively projected to a target map projection plane coordinate system by considering and not considering the implicit characteristics of the converted elements. The method can give consideration to the objective, visual and comprehensive display of the spatial relationship between the topography and the feature elements of the real world.

Description

2.5-dimensional map projection method

Technical Field

The invention relates to the technical field of image processing, in particular to a 2.5-dimensional Chinese mountain-water map projection method based on a scattered point perspective principle.

Background

The landscape painting is an artwork subjected to artificial art abstraction and information processing, can bring visual feeling to artists, but cannot map the real world comprehensively and objectively; the photographic work is a real-world perspective image at a fixed position obtained by photographic equipment, has the characteristics of intuitiveness and reality, but cannot comprehensively represent information of a wider area.

In order to fully and truly display geographic information, a map needs to be made. In the prior art, when a map is manufactured, the environment landform in reality is abbreviated and expressed through a traditional two-dimensional map. The conventional map has a digital line drawing DLG, a digital orthographic image DOM and a relief shading map, namely, the mountain shadow map manufactured by the DEM adopts a downward overlooking view angle perpendicular to the ground, which is beneficial to professionals to objectively grasp the real situation, but is different from a daily oblique side observation view angle, is more abstract to understand, lacks the real feeling brought by a three-dimensional scene, and is inconvenient for common audiences to read the map.

The conventional 2.5-dimensional scene map technology adopts the principle of western focus perspective, and the vision can be converged towards the vanishing point no matter the principle of parallel perspective, angular perspective or three-point perspective is adopted, so that the observed scene has the characteristics of near-large, far-small, near-real, far-virtual and the like, can show the real scene as seen by human eyes, and gives people the feeling of being personally on the scene. However, the method has the defect that the distant scenery cannot be observed in equal proportion, and the equal proportion connection of the ground feature cannot be realized when the field of view moves up, down, left and right, so that the display range of the map cannot be enlarged, and the map can only stay at a fixed observation position and angle, a fixed perspective method and see the near content, but cannot see the distant content and the surrounding content. In summary, the prior art cannot give consideration to the objective, visual and comprehensive presentation of the spatial relationship between the topography and the feature elements of the real world.

Disclosure of Invention

Aiming at the problems in the field, the 2.5-dimensional map projection method can solve the technical problem that the objective, visual and comprehensive spatial relationship between the landform and the feature elements of the real world cannot be displayed.

In order to solve the technical problems, the invention discloses a 2.5-dimensional map projection method, which comprises the following steps:

obtaining DOM raster data, DEM raster data and DLG vector data of original map data; preprocessing the obtained DOM raster data, DEM raster data and DLG vector data to obtain an original image block grid;

according to the principle of scattered point perspective of the Chinese landscape painting, adopting an overhead view angle with the ground to establish a target map projection plane coordinate system; according to the established target map projection plane coordinate system, a certain determined ground three-dimensional point can be vertically projected onto the target map projection plane;

performing projection conversion on the obtained original image block grids to obtain corresponding block target map grids, and transversely splicing the corresponding block target map grids to form projected target map grid data of the DOM full map;

for DLG vector data, when considering the implicit characteristics of the converted elements, generating an implicit background map raster data set by using DEM raster data; according to the grid data set of the invisible background map, vector projections of three geometric types of points, lines and planes are converted into a target map projection plane coordinate system; and directly projecting three geometric element types of points, lines and planes of DLG vector data to a target map projection plane coordinate system when the implicit characteristics of the converted elements are not considered.

Preferably, the preprocessing of the acquired original map data includes the steps of:

converting DOM raster data, DEM raster data and DLG vector data from the coordinate system of the original data thereof to the same plane rectangular coordinate system;

according to the product effect requirement, rotating the sight line direction, and rotating the obtained DOM raster data, DEM raster data and DLG vector data by an angle, and then carrying out subsequent use;

cutting DOM raster data, DEM raster data and DLG vector data by using a uniform geographic range to obtain cut DOM raster data, DEM raster data and DLG vector data;

multiplying the elevation value by a coefficient according to the actual statistical range elevation difference condition;

cutting DOM raster data into a plurality of blocks K in one row and a plurality of columns according to columns ₁ ～K _n 。

Preferably, the establishing the target map projection plane coordinate system includes the following steps:

according to a defined mathematical coordinate system of the real world before map projection, determining O as a coordinate origin, OY as a north coordinate axis, OX as an east coordinate axis and XOY as a map plane before map projection by adopting a scattered point perspective principle of Chinese landscape painting;

a certain determined three-dimensional point of the ground in the real world has coordinates of M (x, y, h), and the coordinates of the point in a plane before map projection are M (x, y);

in the mathematical coordinate system, the projection plane of the conventional orthographic projection is an XOY plane, and the projection direction is an OZ direction;

and rotating the XOY plane by an angle alpha along the X axis, wherein alpha epsilon (0,90) and the formed XOY' plane is the projection plane of the target map.

Preferably, the step of vertically projecting a certain determined ground three-dimensional point onto the target map projection plane includes the following steps:

a certain determined ground three-dimensional point M in the real world is perpendicularly projected onto a target map projection plane XOY ' to form a target map projection point M ' (x ', y '), x is unchanged after projection, y ' is changed due to inclination of a projection plane and elevation of the point M, and the coordinates of the target map projection point are obtained according to the derivation of the geometric relationship:

preferably, the method for obtaining and transversely splicing the corresponding segmented target map grids includes the following steps:

each grid value is obtained from a block grid of DOM grid data from bottom to top, and a grid value pixel center point comprises plane coordinate information (x, y) and color information (r, g, b) at the grid value pixel center point; interpolating in DEM raster data according to the plane coordinates of the raster pixel center point to obtain elevation information (x, y, h) at the point, combining the elevation information and the color information to form spatial texture information M (x, y, h, r, g, b) of the raster pixel center point;

s11, partitioning data K of raster data of DOM ₁ Middle-left to right and bottom-up acquisition of center point information M of each grid pixel ₁ (x,y ₁ ) And obtaining plane coordinates M 'under the projection of the corresponding target map through calculation' ₁ (x,y' ₁ ) Recording the Pointspace texture information into a dataset L ₁₁ (x,y' ₁ ,R ₁ ,G ₁ ,B ₁ )；

S12, judging and marking the point positions behind the mountain and the point positions in front of the mountain, and judging whether the point positions are blocked by the mountain or not; setting M _t (x,y _t ) The highest point of the mountain is the current scanning point position, and the projected coordinate is M' _t (x,y' _t ) Let the initial value y' _t ＝y' ₁ ；

S13, scanning to enter the next pixel M ₂ (x,y2)，M ₂ For the point of upward scanning of DOM raster data, acquiring the center point information M of the next raster pixel ₂ (x,y ₂ ) And calculating to obtain plane coordinates M 'under the projection of the corresponding target map' ₂ (x,y' ₂ )；

S14, if y' ₂ ≤y' _t If true, the central point of the grid pixel is blocked by the highest point in front, and the point information is not recorded and y 'is not modified' _t ；

S15, if y' ₂ ≤y' _t Is false, i.e. y' ₂ >y' _t Indicating that the grid pixel center point is not occluded by the highest point in front, at this time, modify y' _t ＝y' ₂ And sequentially adding the point information to the data set L ₁₂ (x,y' ₂ ,R ₂ ,G ₂ ,B ₂ )；

S16, circulating the steps S13 to S15 until all scanning of the grid of the row is finished, and forming a projected data set L of the grid of the row _1n ；

S17, circulating the steps S11 to S16 until all columns of the grid block are completely scanned, and carrying out L ₁₁ ～L _1n Data merging into a projected data set L of a grid of cost blocks ₁ ；

S18, projecting the data set L according to the block ₁ Acquiring the coordinate range of the projected target map, and designing according to the output gridGround resolution, generally the same as the resolution of the input DOM raster data, creates an empty target projected map grid K' ₁ ；

S19, scanning the target projection map grid K 'from left to right and from bottom to top one by one' ₁ Querying data set S according to location ₁ RGB information nearest to the upper and lower L values in the corresponding columns is weighted by a longitudinal distance, the RGB values of the grid pixels are obtained by interpolation and are filled into a target projection map grid K' ₁ ；

And (3) cycling the steps S11 to S19 until all original image block grids are completely converted into corresponding block target map grids, and transversely splicing all the block target map grids to form the projected target map grid data of the whole image.

Preferably, the generating the hidden background map raster data set by using the DEM raster data includes the following steps:

according to the geographical range and grid spacing specification parameters of the DEM grid data, newly creating grid data with the same specification for indicating whether a certain geographical position is shielded or not, and the grid data is called a hidden background map; the grid is in a single-band gray scale format, whether the position of the grid point N (x, y) is blocked or not is expressed by v, the value is an enumeration value, 1 represents display, and 0 represents blocked, namely the grid point information in the invisible background image is N (x, y, v);

s21, scanning from left to right and from bottom to top in the block data of the DEM raster data to obtain information of each grid point to obtain information M of a first point at the lower left corner ₁ (x ₁ ,y ₁ ,h ₁ ) Obtaining plane coordinates M 'under the projection of the corresponding target map according to calculation' ₁ (x ₁ ,y' ₁ ) Let the grid point information in the corresponding point position revealing background picture be N ₁ (x ₁ ,y ₁ ,1)；

S21, judging whether the grid points scanned subsequently are shielded by the lower mountain body or not and marking; setting y _t The highest point of the mountain before the current scanning point position of the current column is the projected coordinate of y' _t Let the initial value y' _t ＝y' ₁ ；

S22, scanning to enter the next grid point to obtainTake down one grid point information M ₂ (x ₂ ,y ₂ ,h ₂ )，M ₂ The plane coordinate M 'under the projection of the corresponding target map is obtained according to calculation for the point of upward scanning of the DEM raster data' ₂ (x ₂ ,y' ₂ )；

S23, if y' ₂ ≤y' _t Indicating that the point is blocked by the highest point in front, without modifying y' _t Let the grid point information in the corresponding point position revealing background picture be N ₂ (x ₂ ,y ₂ ,0)；

S24, if y' ₂ ≤y' _t Is false, i.e. y' ₂ >y' _t Indicating that the point is not occluded by the highest point before, at which time y 'is modified' _t ＝y' ₂ Let the grid point information in the corresponding point position revealing background picture be N ₂ (x ₂ ,y ₂ ,1)；

S25, the steps S22 to S24 are circulated until all the scanning of the grid of the row is finished, the scanning of the next row is started from the step S21, and finally the grid data set N of the invisible background image is generated.

Preferably, the conversion of the vector projection of the three geometric types of the point, the line and the plane to the target map projection plane coordinate system is that the DLG vector data element respectively carries out vector projection conversion according to the three geometric types of the point element, the line element and the plane element, wherein the conversion method of the annotation reference point element carries out vector projection conversion.

Preferably, the vector projection conversion when considering the implicit features of the converted element includes the following steps:

vector projection conversion when the point elements are apparent and hidden, comprising: reading plane coordinate information M (x, y) from a vector data image layer, obtaining M ' (x, y ') through calculation, searching out hidden information N (x, y, v) of a nearest point location through a hidden background image grid, writing new vector information M ' (x, y ', v) into a projected target file, wherein the point location coordinates are (x, y '), the point location attribute information is an original attribute and an added attribute field visible, and the value of the point location attribute information is v;

vector projection conversion at the time of the salient and implicit features of the line elements, comprising: reading a plane coordinate set S from a vector data image layer, sequentially aiming at point positions M (x, y) of the plane coordinate set S, obtaining M ' (x, y ') through calculation, searching out hidden information N (x, y, v) of the nearest point position through a hidden background image grid, and sequentially storing new point position information M ' (x, y ', v) into the plane coordinate set S ';

sequentially reading a point set S', directly outputting the line string if the implicit identification is consistent, outputting the line string into a plurality of line elements according to the implicit identification in a segmented mode if the implicit identification is inconsistent, writing each line element into a projected target file, wherein the line element coordinates adopt sequential point coordinates, the line element attribute information is an original attribute and an additional attribute field visible, and the value of the line element attribute information is v;

vector projection conversion at the time of the implicit feature of the face element includes: the projection conversion of the plane element is split into projection conversion of the line elements composed of the plane elements, and vector conversion is performed with reference to the line element projections.

Preferably, the vector projection conversion without considering the implicit features of the converted element includes the following steps:

when the implicit identification is not considered, generating an implicit background image without calculation;

directly utilizing coordinates M (x, y) in the point, line and plane vectors, inquiring the DEM grid data to obtain an elevation h, and modifying y into y 'through calculation to form a target projection point M' (x ', y');

and outputting the geometric elements to a vector file, wherein the attribute information is not modified.

Preferably, the method further comprises optimizing the projection conversion formula from y to y', and comprises the following steps:

the geomorphic characteristics are better reflected by adjusting the geomorphic height difference, the elevation H is obtained from the DEM grid data, and the elevation scaling factor s is multiplied by the elevation H to obtain the adjusted elevation H:

H＝h·s

substituting the adjusted elevation H into a map projection formula:

obtaining an optimized target map projection point coordinate formula:

the relief display effect after projection is adjusted by adjusting the rotation angle alpha, if the angle is too large, the shielding elements are too many, and if the angle is too small, the front and back layers among the features are not obvious;

stretching resampling is carried out on the longitudinal direction of the grid result, so that the distance between the drawing area in the longitudinal direction is basically consistent with that before projection, and the Y 'is multiplied by a longitudinal proportionality coefficient m to obtain a stretched Y':

Y'＝y'·m

m＝1/cos(α)

replacing Y 'with Y' to obtain a target map projection point coordinate formula after re-optimization:

wherein x ', y ' are the abscissa and the ordinate of the target projection point M ' (x ', y '), s is the elevation scaling factor, h is the elevation obtained from the DEM raster data, and α is the rotation angle.

Compared with the prior art, the invention has the following beneficial effects:

the invention establishes and projects the coordinate system of the projection plane of the target map, adopts the scattered point perspective principle of the Chinese landscape painting, can vertically project the three-dimensional point on the ground onto the projection plane of the target map, and generates the projection point of the target map of the point, so that scenes at each place can be displayed in equal proportion; performing projection conversion on the original image block grids by adopting an overhead view angle with the ground to obtain corresponding block target map grids, and performing transverse splicing on all the obtained block target map grids to form projected target map grid data of the whole image; the method ensures that the 2.5-dimensional grids can be connected in an equal proportion to realize the expansion of the drawing range, and the manufactured 2.5-dimensional map has the sense of being in the scene and the sense of a stereoscopic sense; meanwhile, the method can also be used for projection conversion of vector elements such as points, lines, planes, marks and the like, and vectors can also have stereoscopic impression and scene impression by generating a hidden background image. The method can project all information of the three-dimensional scene on a two-dimensional plane, can display 2.5-dimensional information of geographic elements, and can enable readers to see side information and interrelation of topography and landform, and meanwhile, the method has the characteristics of objectivity, intuitiveness and comprehensiveness.

Drawings

FIG. 1 is a schematic flow chart of the overall method of the present invention;

fig. 2 is a map projection principle of the present invention, in which:

FIG. 2 (a) is a three-dimensional isometric view of the map projection principle of the present invention;

FIG. 2 (b) is a YOZ side view of the map projection principle of the present invention;

FIG. 3 is a schematic diagram of a raster data projection conversion algorithm according to the present invention;

fig. 4 is a view of a mountain shelter according to the present invention, wherein:

FIG. 4 (a) is a three-dimensional isometric view of a mountain occlusion schematic of the present invention;

fig. 4 (b) is a YOZ side view of a mountain occlusion schematic of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to fig. 1 to 4 in the embodiments of the present invention. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Examples

As shown in fig. 1, an embodiment of the present invention provides a 2.5-dimensional map projection method, including the following steps:

step one, DOM raster data, DEM raster data and DLG vector data in original map data are obtained, wherein:

DOM raster data refers to digital orthographic images capable of providing plane texture information, or raster data such as relief maps, orthoprojected maps, thermodynamic diagrams, effect maps and the like with geographic coordinate information;

DEM raster data refers to digital elevation model raster data that can provide elevation information;

DLG vector data refers to vector digital scribe data that can provide geographical location information, including geometric types as points, lines, facets, notes (points), and the like.

Step two, performing data preprocessing on DOM raster data, DEM raster data and DLG vector data of the obtained original map data to obtain an original map block raster;

1) Coordinate system conversion: converting DOM raster data, DEM raster data and DLG vector data from the coordinate system of the original data thereof to the same plane rectangular coordinate system;

2) Viewing angle conversion: if the visual line direction is required to be rotated according to the product effect requirement, the basic data can be rotated by an angle and then used later;

3) And (5) cutting the range: cutting the data by using a uniform geographic range to obtain DOM raster data, DEM raster data and DLG vector data required by the next step;

4) Elevation treatment: the visual effect of the stretched height difference can be enhanced according to the fact that the height difference condition in the actual statistical range is the multiplication of the height number value and the coefficient;

5) Grid segmentation: cutting DOM raster data into a plurality of blocks (K) ₁ ～K _n ) So that the overall operation efficiency is improved by the subsequent block projection conversion and merging; the DEM raster data may be partitioned if the data size is large.

Thirdly, according to the principle of scattered point perspective of the Chinese landscape painting, adopting an overhead view angle with the ground to establish a target map projection plane coordinate system; according to the established target map projection plane coordinate system, a certain determined ground three-dimensional point can be vertically projected onto the target map projection plane;

1. mathematical coordinate system defining the real world before map projection

As shown in fig. 2 (a), an axial side view of a mathematical coordinate system in the X-axis (eastern direction) is shown, O is a coordinate origin, OY is a north coordinate axis, OX is an east coordinate axis, XOY is a map plane before map projection, three-dimensional coordinates of a ground point in the real world are M (X, y, h), and coordinates of the point in the plane before map projection are M (X, y). In this coordinate system, the projection plane of the normal orthographic projection is an XOY plane, and the projection direction is an OZ direction.

By adopting the principle of scattered point perspective of Chinese landscape painting, the visual line is a parallel line which is at a fixed angle with the ground at any time, the scattered point perspective has no vanishing point, the visual line of each observation point is parallel, and the visual lines are not converged, so that each scene can be displayed in equal proportion, the visual field can be infinitely translated up and down and left and right in the visual plane, the map display range is enlarged without influencing the display proportion of the ground, and all contents in the drawing area can be displayed in equal proportion.

2. Establishment and projection of plane coordinate system of target projection map

Rotating the XOY plane in the figure 2 (a) by an angle alpha along the X axis, wherein the alpha epsilon (0,90) forms an XOY' plane which is the projection plane of the target map provided by the application;

the ground three-dimensional point M in the real world is vertically projected onto the target map projection plane XOY ' to form a target map projection point M ' (x ', y '), x is unchanged after projection, y ' is changed due to inclination of the projection plane and elevation of the point M, as shown in fig. 2 (b), the coordinates of the target map projection point are obtained according to the derivation of the geometric relationship:

step four, according to a certain target map projection point of a certain determined ground three-dimensional point, adopting an overhead view angle with the ground, and performing projection conversion on the obtained original map block grid to obtain a corresponding block target map grid;

the method for obtaining the corresponding block target map grid comprises the following steps of:

each grid value is obtained from DOM grid data column by column from bottom to top, and the grid value pixel center point comprises plane coordinate information (x, y) and color information (r, g, b) at the grid value pixel center point; interpolating elevation information (x, y, h) at the grid value pixel center point in DEM grid data according to the plane coordinates of the grid value pixel center point, combining the elevation information and the color information to form spatial texture information M (x, y, h, r, g, b) of the grid value pixel center point, as shown in fig. 3;

1) Blocking data K from DOM raster data ₁ Middle-left to right and bottom-up acquisition of center point information M of each grid pixel ₁ (x,y ₁ ) And obtaining plane coordinates M 'under the projection of the corresponding target map through calculation' ₁ (x,y' ₁ ) Recording the Pointspace texture information into a dataset L ₁₁ (x,y' ₁ ,R ₁ ,G ₁ ,B ₁ )；

2) Because the mountain is blocked, the point position behind the mountain may be blocked by the mountain, and therefore, judgment and marking are needed to judge whether the point position is blocked by the mountain or not, as shown in fig. 4 (a) and 4 (b); setting M _t (x,y _t ) The highest point of the mountain is the current scanning point position, and the projected coordinate is M' _t (x,y' _t ) Let the initial value y' _t ＝y' ₁ ；

3) Scanning into the next pixel M ₂ (x,y ₂ )，M ₂ For the point of upward scanning of DOM raster data, acquiring the center point information M of the next raster pixel ₂ (x,y ₂ ) And calculating to obtain plane coordinates M 'under the projection of the corresponding target map' ₂ (x,y' ₂ )；

4) If y' ₂ ≤y' _t If true, the central point of the grid pixel is blocked by the highest point in front, and the point information is not recorded and y 'is not modified' _t ；

5) If y' ₂ ≤y' _t Is false, i.e. y' ₂ >y' _t Indicating that the grid pixel center point is not occluded by the highest point in front, at this time, modify y' _t ＝y' ₂ And sequentially adding the point information to the data set L ₁₂ (x,y' ₂ ,R ₂ ,G ₂ ,B ₂ )；

6) Cycling the above steps 3) to 5) until all scans of the grid of the present column are completed, forming a projected data set L of the grid of the present column _1n ；

7) Cycling through the steps 1) to 6) until all columns of the block grid are scanned completely, and then L ₁₁ ～L _1n DataCombining the projected data sets L forming a grid of cost blocks ₁ ；

8) According to the projected dataset L of the block ₁ The coordinate range of the projected target map is obtained, the ground resolution is designed according to the output grid, the ground resolution is generally the same as the resolution of the input DOM grid data, and an empty target projection map grid K 'is established' ₁ ；

9) Scanning the target projection map grid K 'from left to right and from bottom to top pixel by pixel' ₁ Querying data set S according to location ₁ RGB information nearest to the upper and lower L values in the corresponding columns is weighted by a longitudinal distance, the RGB values of the grid pixels are obtained by interpolation and are filled into a target projection map grid K' ₁ ；

And (3) cycling the steps 1) to 9) until all original image block grids are completely converted into corresponding block target map grids, and transversely splicing all the block target map grids to form the projected target map grid data of the whole image.

The map projection conversion of the vector data includes the steps of:

and generating a saliency background image by using the DEM raster data, and respectively carrying out vector projection conversion on the saliency characteristic conditions of the elements after conversion or not according to three geometric types of points, lines and planes, wherein the conversion method of the annotation reference point elements carries out vector projection conversion.

Definition of a latent background map

According to the geographical range and grid spacing specification parameters of the DEM grid data, newly creating grid data with the same specification for indicating whether a certain geographical position is shielded or not, and the grid data is called a hidden background map; the grid is in a single-band gray scale format, whether the position of the grid point N (x, y) is blocked or not is expressed by v, the value is an enumeration value, 1 represents display, and 0 represents blocked, namely the grid point information in the invisible background image is N (x, y, v);

a) Scanning from left to right and from bottom to top in the partitioned data of the DEM raster data to obtain the information of each lattice point to obtain the information M of the first point of the lower left corner ₁ (x ₁ ,y ₁ ,h ₁ ) Obtaining the plane sitting under the projection of the corresponding target map according to the calculationMark M' ₁ (x ₁ ,y' ₁ ) Let the grid point information in the corresponding point position revealing background picture be N ₁ (x ₁ ,y ₁ ,1)；

b) Judging whether the grid points scanned subsequently are shielded by the lower mountain and marking; setting y _t The highest point of the mountain before the current scanning point position of the current column is the projected coordinate of y' _t Let the initial value y' _t ＝y' ₁ ；

c) Scanning to enter the next grid point to acquire the information M of the next grid point ₂ (x ₂ ,y ₂ ,h ₂ )，M ₂ For the point of upward scanning of DEM raster data, calculating according to formula (1) to obtain plane coordinate M 'under the projection of the corresponding target map' ₂ (x ₂ ,y' ₂ )；

d) If y' ₂ ≤y' _t Indicating that the point is blocked by the highest point in front, without modifying y' _t Let the grid point information in the corresponding point position revealing background picture be N ₂ (x ₂ ,y ₂ ,0)；

e) If y' ₂ ≤y' _t Is false, i.e. y' ₂ >y' _t Indicating that the point is not occluded by the highest point before, at which time y 'is modified' _t ＝y' ₂ Let the grid point information in the corresponding point position revealing background picture be N ₂ (x ₂ ,y ₂ ,1)；

f) And c) cycling the steps c) to e) until all the scanning of the grid of the row is finished, and starting the scanning of the next row from the step a), and finally generating the grid data set N of the invisible background graph.

The projection conversion is divided into three geometric types of vector projection conversion of points, lines and planes which consider the implicit features and three geometric types of vector projection conversion of points, lines and planes which do not consider the implicit features, and the two geometric types of vector projection conversion are analyzed, in particular:

case one: the vector projection conversion of three geometric types of points, lines and planes considering the implicit features comprises the following steps:

the point element reads plane coordinate information M (x, y) from the vector data image layer, obtains M ' (x, y ') through calculation, searches out the hidden information N (x, y, v) of the nearest point location through a hidden background image grid, writes new vector information M ' (x, y ', v) into a projected target file, and the point location coordinate is (x, y '), and the point location attribute information is the original attribute and an additional attribute field visible, and the value of the point location attribute information is v;

line elements, reading a plane coordinate set S from a vector data image layer, sequentially aiming at point positions M (x, y) of the plane coordinate set S, obtaining M ' (x, y ') through calculation, searching out revealing information N (x, y, v) of the nearest point position through a revealing background image grid, and sequentially storing new point position information M ' (x, y ', v) into the plane coordinate set S ';

sequentially reading a point set S', directly outputting the line string if the implicit identification is consistent, outputting the line string into a plurality of line elements according to the implicit identification in a segmented mode if the implicit identification is inconsistent, writing each line element into a projected target file, wherein the line element coordinates adopt sequential point coordinates, the line element attribute information is an original attribute and an additional attribute field visible, and the value of the line element attribute information is v;

the plane element consists of at least one outer ring and zero or a plurality of inner rings, and the complex plane is formed by nesting and combining other planes, so that the projection conversion of the plane element is also split into the projection conversion of the line elements formed by the plane element, and the projection conversion of the line elements is specifically referred to.

And a second case: the vector projection conversion of three geometric types of points, lines and planes without considering the implicit features comprises the following steps:

when the implicit identification is not considered, generating an implicit background image without calculation;

directly utilizing coordinates M (x, y) in the point, line and plane vectors, inquiring DEM raster data to obtain an elevation h, and calculating and modifying y into y' through a formula (1);

and outputting the geometric elements to a vector file, wherein the attribute information is not modified.

The map projection algorithm is the most basic and core algorithm flow, and can be properly adjusted and expanded according to the specific technical implementation mode, the technical requirement of products or the requirement of artistic effect in actual implementation. The projection conversion formula from y to y' in the formula (1) can be optimized, and the specific optimization process comprises the following steps:

because the relative height difference between the features is generally much smaller than the length and width of the drawing area, when the feature features of the large-area drawing area are reflected, the high-low contrast of the features cannot be displayed by directly utilizing the formula (1), and the feature features can be better reflected by increasing the height difference of the features.

Specifically, an elevation H is obtained from DEM raster data, and the elevation scaling factor s is multiplied by H using formula (2), so as to obtain an adjusted elevation H:

H＝h·s (2)

substituting the adjusted elevation H into H in the formula (1):

further obtaining an adjusted map projection formula:

the relief display effect after projection can be adjusted by adjusting the rotation angle alpha, if the angle is too large, the shielding elements are too many, and if the angle is too small, the front and back layers among the features are not obvious;

the projection algorithm described above may cause the distance compression in the ordinate direction after projection to be reduced, so in order to take into account the general impression of the reader on the shape of the drawing area, the longitudinal direction of the grid result may be stretch resampled to y' multiplied by the longitudinal scaling factor m:

Y'＝y'·m (5)

m＝1/cos(α) (6)

the distance between the drawing areas in the longitudinal direction is basically consistent with that before projection;

substituting equation (5) and equation (6) into equation (3) and substituting Y 'for Y' yields a practical equation from which the optimization can be derived:

where s is an elevation scaling factor, h is an elevation obtained from DEM raster data, and α is a rotation angle. Generally, s takes a value of 2-3.

In general, the most commonly used method is to take α=45°, s=2, simplify the formula (7), and obtain a simplified practical formula:

substituting the simplified practical formula (8) into the projection conversion calculation process in place of the formula (1), performing block projection and splicing according to original DOM raster data to obtain target map raster data, performing projection according to the original DEM raster data to obtain a hidden background map raster data set, and performing projection by combining the original DLG vector data with the hidden background map raster data set to generate target map vector data. The method projects the three-dimensional scene information onto a two-dimensional plane, and a 2.5-dimensional map is obtained.

The map manufactured by the map projection method provided by the application adopts an overhead view angle with the ground, can display a three-dimensional scene on a two-dimensional plane, can display 2.5-dimensional information of geographic elements, and can see side information and interrelationships of topography and landform.

Compared with the conventional map and the orthographic image which only show top overlook information, the map manufactured by the method has the stereoscopic impression and scene impression of being in the scene, and readers can feel the relief of the topography and the spatial relationship of the geographic elements more intuitively.

Compared with landscapes, photographic works, conventional 2.5-dimensional perspective scene maps and the like, the map manufactured by the method can be connected in equal proportion to realize expansion of the drawing range and comprehensive and objective display of visual scenes.

The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.

In addition, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methodologies associated with the documents. In case of conflict with any incorporated document, the present specification will control.

Claims (10)

1. A 2.5-dimensional map projection method, comprising the steps of:

obtaining DOM raster data, DEM raster data and DLG vector data of original map data; preprocessing the obtained DOM raster data, DEM raster data and DLG vector data to obtain an original image block grid;

according to the principle of scattered point perspective of the Chinese landscape painting, adopting an overhead view angle with the ground to establish a target map projection plane coordinate system; according to the established coordinate system of the projection plane of the target map, vertically projecting a certain determined ground three-dimensional point onto the projection plane of the target map;

performing projection conversion on the obtained original image block grids to obtain corresponding block target map grids, and transversely splicing the corresponding block target map grids to form projected target map grid data of the DOM full map;

for DLG vector data, when considering the implicit characteristics of the converted elements, generating an implicit background map raster data set by using DEM raster data; according to the grid data set of the invisible background map, vector projections of three geometric types of points, lines and planes are converted into a target map projection plane coordinate system; and directly projecting three geometric element types of points, lines and planes of DLG vector data to a target map projection plane coordinate system when the implicit characteristics of the converted elements are not considered.

2. The 2.5-dimensional map projection method according to claim 1, wherein the preprocessing of the acquired raw map data comprises the steps of:

converting DOM raster data, DEM raster data and DLG vector data from the coordinate system of the original data thereof to the same plane rectangular coordinate system;

according to the product effect requirement, rotating the sight line direction, and rotating the obtained DOM raster data, DEM raster data and DLG vector data by an angle, and then carrying out subsequent use;

cutting DOM raster data, DEM raster data and DLG vector data by using a uniform geographic range to obtain cut DOM raster data, DEM raster data and DLG vector data;

multiplying the elevation value by a coefficient according to the actual statistical range elevation difference condition;

cutting DOM raster data into a plurality of blocks K in one row and a plurality of columns according to columns ₁ ～K _n 。

3. The 2.5-dimensional map projection method according to claim 2, wherein the establishing a target map projection plane coordinate system comprises the steps of:

according to a defined mathematical coordinate system of the real world before map projection, determining O as a coordinate origin, OY as a north coordinate axis, OX as an east coordinate axis and XOY as a map plane before map projection by adopting a scattered point perspective principle of Chinese landscape painting;

a certain determined three-dimensional point of the ground in the real world has coordinates of M (x, y, h), and the coordinates of the point in a plane before map projection are M (x, y);

in the mathematical coordinate system, the projection plane of the conventional orthographic projection is an XOY plane, and the projection direction is an OZ direction;

and rotating the XOY plane by an angle alpha along the X axis, wherein alpha epsilon (0,90) and the formed XOY' plane is the projection plane of the target map.

4. A 2.5-dimensional map projection method according to claim 3, characterized in that said vertically projecting a certain determined ground three-dimensional point onto a target map projection plane comprises the steps of:

a certain determined ground three-dimensional point M in the real world is perpendicularly projected onto a target map projection plane XOY ' to form a target map projection point M ' (x ', y '), x is unchanged after projection, y ' is changed due to inclination of a projection plane and elevation of the point M, and the coordinates of the target map projection point are obtained according to the derivation of the geometric relationship:

5. the 2.5-dimensional map projection method of claim 4, wherein the obtaining and transversely stitching the corresponding segmented target map grid comprises the steps of:

each grid value is obtained from a block grid of DOM grid data from bottom to top, and a grid value pixel center point comprises plane coordinate information (x, y) and color information (r, g, b) at the grid value pixel center point; interpolating in DEM raster data according to the plane coordinates of the raster pixel center point to obtain elevation information (x, y, h) at the point, combining the elevation information and the color information to form spatial texture information M (x, y, h, r, g, b) of the raster pixel center point;

s11, partitioning data K of raster data of DOM ₁ Middle-left to right and bottom-up acquisition of center point information M of each grid pixel ₁ (x,y ₁ ) And obtaining plane coordinates M 'under the projection of the corresponding target map through calculation' ₁ (x,y' ₁ ) Recording the Pointspace texture information into a dataset L ₁₁ (x,y′ ₁ ,R ₁ ,G ₁ ,B ₁ )；

S12, judging and marking the point positions behind the mountain and the point positions in front of the mountain, and judging whether the point positions are blocked by the mountain or not; setting M _t (x,y _t ) The highest point of the mountain is the current scanning point position, and the projected coordinate is M' _t (x,y' _t ) Let the initial value y' _t ＝y' ₁ ；

S13, scanning to enter the next pixel M ₂ (x,y2)，M ₂ For the point of upward scanning of DOM raster data, acquiring the center point information M of the next raster pixel ₂ (x,y ₂ ) And calculating to obtain plane coordinates M 'under the projection of the corresponding target map' ₂ (x,y' ₂ )；

S14, if y' ₂ ≤y' _t If true, the central point of the grid pixel is blocked by the highest point in front, and the point information is not recorded and y 'is not modified' _t ；

S15, if y' ₂ ≤y' _t Is false, i.e. y' ₂ >y' _t Indicating that the grid pixel center point is not occluded by the highest point in front, at this time, modify y' _t ＝y' ₂ And sequentially adding the point information to the data set L ₁₂ (x,y' ₂ ,R ₂ ,G ₂ ,B ₂ )；

S16, circulating the steps S13 to S15 until all scanning of the grid of the row is finished, and forming a projected data set L of the grid of the row _1n ；

S17, circulating the steps S11 to S16 until all columns of the grid block are completely scanned, and carrying out L ₁₁ ～L _1n Data merging into a projected data set L of a grid of cost blocks ₁ ；

S18, projecting the data set L according to the block ₁ The coordinate range of the projected target map is obtained, the ground resolution is designed according to the output grid, the ground resolution is generally the same as the resolution of the input DOM grid data, and an empty target projection map grid K 'is established' ₁ ；

S19, scanning the target projection map grid K 'from left to right and from bottom to top one by one' ₁ Querying data set S according to location ₁ RGB information nearest to the upper and lower L values in the corresponding columns is weighted by a longitudinal distance, the RGB values of the grid pixels are obtained by interpolation and are filled into a target projection map grid K' ₁ ；

And (3) cycling the steps S11 to S19 until all original image block grids are completely converted into corresponding block target map grids, and transversely splicing all the block target map grids to form the projected target map grid data of the whole image.

6. The 2.5-dimensional map projection method of claim 5, wherein the generating a hidden background map raster data set using DEM raster data includes the steps of:

according to the geographical range and grid spacing specification parameters of the DEM grid data, newly creating grid data with the same specification for indicating whether a certain geographical position is shielded or not, and the grid data is called a hidden background map; the grid is in a single-band gray scale format, whether the position of the grid point N (x, y) is blocked or not is expressed by v, the value is an enumeration value, 1 represents display, and 0 represents blocked, namely the grid point information in the invisible background image is N (x, y, v);

s21, scanning from left to right and from bottom to top in the block data of the DEM raster data to obtain information of each grid point to obtain information M of a first point at the lower left corner ₁ (x ₁ ,y ₁ ,h ₁ ) Obtaining plane coordinates M 'under the projection of the corresponding target map according to calculation' ₁ (x ₁ ,y' ₁ ) Let the grid point information in the corresponding point position revealing background picture be N ₁ (x ₁ ,y ₁ ,1)；

S21, judging whether the grid points scanned subsequently are shielded by the lower mountain body or not and marking; setting y _t The highest point of the mountain before the current scanning point position of the current column is the projected coordinate of y' _t Let the initial value y' _t ＝y' ₁ ；

S22, scanning to enter the next grid point, and obtaining the information M of the next grid point ₂ (x ₂ ,y ₂ ,h ₂ )，M ₂ The plane coordinate M 'under the projection of the corresponding target map is obtained according to calculation for the point of upward scanning of the DEM raster data' ₂ (x ₂ ,y' ₂ )；

S23, if y' ₂ ≤y' _t Indicating that the point is blocked by the highest point in front, without modifying y' _t Let the grid point information in the corresponding point position revealing background picture be N ₂ (x ₂ ,y ₂ ,0)；

S24, if y' ₂ ≤y' _t Is false, i.e. y' ₂ >y' _t Indicating that the point is not occluded by the highest point before, at which time y 'is modified' _t ＝y' ₂ Let the grid point information in the corresponding point position revealing background picture be N ₂ (x ₂ ,y ₂ ,1)；

S25, the steps S22 to S24 are circulated until all the scanning of the grid of the row is finished, the scanning of the next row is started from the step S21, and finally the grid data set N of the invisible background image is generated.

7. The 2.5-dimensional map projection method according to claim 6, wherein the conversion of the vector projections of three geometric types of points, lines and planes into the target map projection plane coordinate system is that DLG vector data elements respectively perform vector projection conversion according to three geometric types of point elements, line elements and plane elements, wherein the conversion method of annotation reference point elements performs vector projection conversion.

8. The 2.5-dimensional map projection method according to claim 7, wherein the vector projection conversion in consideration of the implicit features of the converted elements comprises the steps of:

vector projection conversion when the point elements are apparent and hidden, comprising: reading plane coordinate information M (x, y) from a vector data image layer, obtaining M ' (x, y ') through calculation, searching out hidden information N (x, y, v) of a nearest point location through a hidden background image grid, writing new vector information M ' (x, y ', v) into a projected target file, wherein the point location coordinates are (x, y '), the point location attribute information is an original attribute and an added attribute field visible, and the value of the point location attribute information is v;

vector projection conversion at the time of the salient and implicit features of the line elements, comprising: reading a plane coordinate set S from a vector data image layer, sequentially aiming at point positions M (x, y) of the plane coordinate set S, obtaining M ' (x, y ') through calculation, searching out hidden information N (x, y, v) of the nearest point position through a hidden background image grid, and sequentially storing new point position information M ' (x, y ', v) into the plane coordinate set S ';

sequentially reading a point set S', directly outputting the line string if the implicit identification is consistent, outputting the line string into a plurality of line elements according to the implicit identification in a segmented mode if the implicit identification is inconsistent, writing each line element into a projected target file, wherein the line element coordinates adopt sequential point coordinates, the line element attribute information is an original attribute and an additional attribute field visible, and the value of the line element attribute information is v;

vector projection conversion at the time of the implicit feature of the face element includes: the projection conversion of the plane element is split into projection conversion of the line elements composed of the plane elements, and vector conversion is performed with reference to the line element projections.

9. The 2.5-dimensional map projection method according to claim 8, wherein the vector projection conversion without considering the implicit features of the converted elements comprises the steps of:

when the implicit identification is not considered, generating an implicit background image without calculation;

directly utilizing coordinates M (x, y) in the point, line and plane vectors, inquiring the DEM grid data to obtain an elevation h, and modifying y into y 'through calculation to form a target projection point M' (x ', y');

and outputting the geometric elements to a vector file, wherein the attribute information is not modified.

10. The 2.5-dimensional map projection method of claim 9, further comprising optimizing the projection conversion formula of y to y', comprising the steps of:

the geomorphic characteristics are better reflected by adjusting the geomorphic height difference, the elevation H is obtained from the DEM grid data, and the elevation scaling factor s is multiplied by the elevation H to obtain the adjusted elevation H:

H＝h·s

substituting the adjusted elevation H into a map projection formula:

obtaining an optimized target map projection point coordinate formula:

the relief display effect after projection is adjusted by adjusting the rotation angle alpha, if the angle is too large, the shielding elements are too many, and if the angle is too small, the front and back layers among the features are not obvious;

stretching resampling is carried out on the longitudinal direction of the grid result, so that the distance between the drawing area in the longitudinal direction is basically consistent with that before projection, and the Y 'is multiplied by a longitudinal proportionality coefficient m to obtain a stretched Y':

Y′＝y′·m

m＝1/cos(α)

replacing Y 'with Y' to obtain a target map projection point coordinate formula after re-optimization:

wherein x ', y ' are the abscissa and the ordinate of the target projection point M ' (x ', y '), s is the elevation scaling factor, h is the elevation obtained from the DEM raster data, and α is the rotation angle.