CN101887451A - Simplifying method of electronic chart vector graph - Google Patents
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Abstract
The invention provides a simplifying method of an electronic chart vector graph, which comprises the steps of: (1) extracting a convex hull of a given vector graph; (2) processing a graphic convex part and a graphic concave part, which are divided from the convex hull, in a classification way; (3) simplifying the graphic convex part by directly applying a Douglas-Peucker algorithm; and simplifying the graphic concave part with a method for simplification by layers, and for the concave part with complex bend, identifying the bends in different layers by applying a bend identification method based on a linear portion winding direction and then simplifying the bend in each layer respectively until all the bends are processed; and (4) adding a simplifying threshold, and carrying out the simplification on the concave part. The invention is a method for simplifying a vector graph through a mode for reducing description vector graphic data points on the premise of keeping the geometrical shape of the vector graph unchanged, and effectively overcomes the defect of self-intersection easily occurring in the traditional simplifying algorithm.
Description
Technical field
What the present invention relates to is Geographic Information System spatial data analysis and disposal route.
Background technology
Electronic chart system (Electronic Chart System.ECS) is the real-time navigation infosystem of a kind of integrated form of producing along with the development of seafaring, is considered to another great technological revolution in the navigation field over nearly 10 years after radar/ARPA.Definition according to International Hydrography Organization (IHO): the electronic chart system is a kind of with nautical chart information, locating information, radar information, the boats and ships dynamic parameter navigation automated system that both pictures and texts are excellent that is integrated in one.It is made of electronic chart data file, control display device, special software and external sensor.
The electronic chart system is as the display platform of marine information, and the actual atural object characteristic information in marine site is specified in description that can be detailed.Key elements such as island are present in the sea chart in a large number, and in vector electronic chart now, what describe island isovector key element use is a series of intensive discrete point ranges.Because data point is many more, the ability of describing original atural object is strong more, can reflect the original really more.Therefore, in the chart data file, store a large amount of point data, be used for the morphological feature on detailed description island.
Growing along with the electronic chart technology, its application constantly enlarges.By front narration as can be known, what describe in the electronic chart that key element such as island uses is the series of discrete point data, and in concrete practical application, the data of directly using magnanimity in the sea chart are carried out mathematical computations and will inevitably be caused the slow and inefficiency of arithmetic speed.For example, in the application-specific of when electronic chart is served nearly water surface flying device routeing, island etc. being evaded, using in the vector sea chart a large amount of point data for path planning, to carry out the obvious data volume of routeing too big, evades when taking machine when calculating too much, and efficient is extremely low.For this reason, be necessary a large amount of point data of describing key elements such as island promptly the sea chart key element to be simplified processing in the extraction that guarantees to carry out under the constant prerequisite of its geometric configuration unique point.
The electronic chart vector graph abbreviation belongs to the category of vector data compression.At present, from the documents and materials of collecting, the algorithm that relevant vector graphics is simplified mostly concentrates on map automatic Synthesis field.In this field, usually take the technology realization essential factors space information of vector data compression and the self-adaptation of map scale, map scale big (scale denominator is bigger) even, the data volume of then describing key element is big, if reduce map scale, then reduce the data volume of describing same key element, factor data information and map scale are adapted to mutually by certain algorithm.Anatomize existing vector graphics shortcut calculation and can find out clearly that all there is certain defective in current algorithm, mainly shows: intersecting may appear in the figure behind (1) abbreviation; (2) problem of choosing of abbreviation threshold value.
The Douglas-Peucker algorithm is as the vector graphics abbreviation classic algorithm of generally acknowledging at present, propose in 1973 by D.Douglas and T.Peucker, be called for short the D-P algorithm, in the existing abbreviation algorithm, have quite a few all on this algorithm basis, to improve generation.Its advantage is to have translation and rotational invariance, and after given curve and the threshold value, the abbreviation result is certain.This basic idea is: prior given threshold value δ, and line between 2 on curve head, end calculates intermediate point successively to the distance of this line segment, finds out the ultimate range point, and whether judges this distance less than δ, if then cast out all intermediate points of this curve; Otherwise, keep this point, and be the boundary with this point, curve is divided into two parts, these two parts are reused aforesaid operations.From basic thought as can be seen this method have tangible recursive nature, be a kind of by integral body to local, the method for abbreviation vector graphics from coarse to fine.
The Douglas-Peucker algorithm has obtained to use widely in different fields.For example, application number is to use this algorithm in 200810243866 the patented claim to have realized a kind of electronic map data processing method, directly adopted the Douglas-Peucker algorithm to carry out the vector data compression in this application, do not consider the defective (there is self intersection in the possibility of result behind the abbreviation, the problem such as suitably choose of abbreviation threshold value) and the limitation on application-specific of Douglas-Peucker algorithm self.
The basic goal of vector graphics abbreviation is under the prerequisite that keeps the figure essential characteristic, by reducing the quantity of the point that constitutes figure, finishes the abbreviation of figure.For the abbreviation process, should follow " three maintenances ": the one, keep the similarity of figure before and after the abbreviation, promptly keep the essential characteristic of curved shape; The 2nd, the accuracy of maintenance bending features turning point; The 3rd, the contrast that keeps different locations degree of crook.
Summary of the invention
The object of the present invention is to provide a kind of more complete, accurate, simplifying method of electronic chart vector graph that versatility is stronger.
The object of the present invention is achieved like this:
(1) extracts the convex hull of given vector graphics;
(2) will handle by figure protuberance and recess classification that convex hull marks off, carry out abbreviation respectively;
(3) directly use the Douglas-Peucker algorithm figure protuberance is carried out abbreviation; The figure recess adopts successively the method for abbreviation to carry out abbreviation, for the recess that has complicated bend, application identifies the bending of different levels based on the crooked recognition methods of straight-line segment moving direction, then abbreviation is carried out in the bending of each level respectively, finishes until all bending processes;
(4), increase an abbreviation threshold value, implement abbreviation to recess.
The present invention be directed to defectives such as using the figure self intersection that may occur when basic Douglas-Peucker algorithm carries out the vector graphics abbreviation and figure recess conformality difference, in conjunction with the needs of vector graphics abbreviation in the electronic chart, the new vector graphics simplifying method of design.The notable feature that the method that provides among the present invention is different from existing method is: adopt the method for extracting convex hull and improving the Douglas-Peucker algorithm to guarantee whole and local (particularly recess) conformality of the figure behind the abbreviation effectively; Take based on the crooked recognition methods of straight-line segment moving direction and the crooked mode of abbreviation successively, can fundamentally solve the self intersection problem that figure may occur behind the abbreviation.This method comprises following main points:
1, extracts the convex hull of given vector graphics.Because convex hull can be described the basic geometric shape of figure preferably, therefore at first treat the figure of abbreviation and set up convex hull, utilize the configuration characteristics of convex hull identification figure, especially, convex hull can give expression to the flexural property of figure;
2, will handle by figure protuberance and recess classification that convex hull marks off, carry out abbreviation respectively.Because the data point major part of describing vector graphics concentrates on the recess of figure, be used to describe in detail the bending shape feature of figure, and the protuberance number of data points is less, therefore can directly use the Douglas-Peucker algorithm carries out abbreviation to the figure protuberance.For recess, by putting 3 described method abbreviations;
3, the figure recess adopts successively the method for abbreviation to carry out abbreviation.For the recess that has complicated bend, can use the bending that identifies different levels based on the crooked recognition methods (implementation procedure of this method is seen the embodiment part) of straight-line segment moving direction, then abbreviation is carried out in the bending of each level respectively, finish until all bending processes.Can effectively avoid the figure behind the abbreviation self intersection phenomenon to occur by this method.
4, increase an abbreviation threshold value, implement abbreviation recess.When application enhancements Douglas-Peucker algorithm carries out abbreviation to the figure recess, on the basis of traditional algorithm, increase a width threshold value control abbreviation process.Determine to describe the choice at number of bends strong point jointly by the crooked degree of depth and two threshold values of width.
Beneficial effect of the present invention is embodied in: to the simplification of vector graphics, mainly be to handle at the abbreviation of figure recess.Among the present invention, convex hull by making up figure and adopt the bending that can successively decomposite the figure recess based on the crooked recognition methods of straight-line segment moving direction, carry out abbreviation respectively at each bending, can measure crooked feature exactly and carry out to greatest extent and rational abbreviation, thereby improve the conformality of figure behind the abbreviation.Each bending that the present invention adopts the method based on straight-line segment moving direction to identify all is the star region, and by sufficient theoretical proof, the star region carries out self intersection can not occurring behind the abbreviation, so the present invention has solved the defective that traditional abbreviation algorithm is prone to self intersection effectively.
Description of drawings
Fig. 1 is the process flow diagram of vector graphics short-cut method of the present invention.
The performing step of the polygon convex hull generating algorithm that Fig. 2 A-2B is used for explaining that the present invention adopts.
Fig. 3 is used to illustrate the method based on straight-line segment perturbation direction identification curved.
Fig. 4 A-4F is respectively island original shape (4A), island convex hull (4B) and the abbreviation of taking different abbreviation threshold values figure (4C-4F) as a result.
Fig. 5 is C10013 sea chart island data abbreviation result's part figure.
Embodiment
For example the present invention is done description in more detail below in conjunction with accompanying drawing:
The invention discloses a kind of electronic chart vector graph simplifying method, the concrete implementation content of this method comprises the structure convex hull, and is crooked and use the improvement Douglas-Peucker algorithm that proposes to vector graphics key content such as abbreviation successively based on straight-line segment moving direction identification.Below in detail the embodiment of the technical scheme of the present invention's proposition will be described in detail according to the abbreviation flow process, the abbreviation flow process as shown in Figure 1.This embodiment mainly comprises following committed step:
One, makes up convex hull
Convex hull is the natural limit border of data point set, for comprising the minimal convex polygon of all data points, connects any line segment at 2 and must be arranged in this convex polygon fully, also reaches minimum value with the area of time domain.Computing method about convex hull are a lot, can introduce the polygon convex hull generating algorithm of using among the present invention below referring to the books of computational geometry, computer graphics aspect, and this algorithm comprises following two steps:
Step 1: for given polygon, find out the point of ordinate minimum in all data points, be designated as p
1If from p
1Beginning polygon oriented vertex sequence along clockwise direction is (p
1, p
2..., p
n).
Step 2: search convex hull summit: note p
1Be the summit on first convex hull, then from directed line segment p
1p
2Begin to search, if polygonal all summits are all at directed line segment p
1p
2The right side, p then
2Also be the convex hull summit, otherwise search directed line segment p in turn
1p
3, p
1p
4..., satisfy polygonal all summits all at p until finding
1p
iThe some p on right side
i, then remember p
iBe the convex hull summit, then from p
iBeginning is according to above-mentioned and p
1Begin same step and search the convex hull summit in turn, up to returning p
1Till the point, write down all convex hull summits successively, and line has just been finished the generative process of polygon convex hull in turn.As Fig. 2 A and Fig. 2 B, initial polygon vertex is (p
1, p
2..., p
9), the convex hull summit of generation is (p
1, p
2, p
4, p
7, p
9, p
10).
Two, crooked based on the identification of straight-line segment moving direction
Crooked recognition methods has a variety of, for example discerns bending etc. based on flex point identification bending and the crooked method of dividing of employing cable-stayed type.Different crooked recognition methodss are applicable to different applied environments.At requirement and the characteristics that vector graphics in the electronic chart is simplified, use based on the method identification of straight-line segment moving direction crooked.In sea chart, describe vector graphics, stipulate that these data points have formed a point set C={P according to clockwise order by a series of continuous data points
1, P
2..., P
N-1, P
n, P wherein
1Be the starting point of curve, P
nTerminal point for curve.P
1And P
n2 coincidences represent that this point set is the curve of a closure.
Regulation: for given curve S=(v
0..., v
n) (0≤n＜∞), S
k=(v
i..., v
j) ∈ S, (i＜j), if node v
i, v
jWith node v
I+1..., v
J-1The moving direction of place straight-line segment is opposite, then S
kBe exactly a bending of curve S, node v
iBe this crooked starting point, node v
jIt is this crooked terminal point.
Among Fig. 3, curve is by p
1, p
2..., p
12Totally 12 points are formed."+" and "-" represent on the curve two the different moving directions of a follow-up straight-line segment with respect to current straight-line segment respectively.Be without loss of generality, setting to the clockwise direction moving is "+", for example p
2The point place; To the counter clockwise direction moving is "-", for example p
3The point place.Then the some place that changes with moving point direction can mark off differently curved as separation.As Fig. 3, some p
2, p
3, p
4, p
5, p
6Constituted a bending; Point p
8, p
9, p
10, p
11Constituted another bending.
Three, the process of abbreviation successively of figure recess (bending)
Convex hull has marked off a series of protuberance and recess with vector graphics, and we divide protuberance and recess to come and carry out abbreviation respectively and handle.For protuberance, can directly adopt the Douglas-Peucker algorithm to carry out abbreviation.For recess, owing to there is the situation of complicated bend, need the middle crooked recognition methods of describing of utilization (2) to identify the bending of different levels, then abbreviation is carried out in the bending of each level respectively, finish until all bending processes based on straight-line segment moving direction.Details are as follows for the specific implementation step of curve recess abbreviation:
Step 1: carry out bending for given curve and divide, identify the bending of first level;
Step 2: whether judge crooked number greater than 1, if not, then the bending of this curve composition is a simple bending, and directly abbreviation gets final product.Otherwise, carry out abbreviation respectively for each bending, and write down the process information (whether behind abbreviation, keeping) of each data point.
Step 3: behind the crooked abbreviation of first level, traversal does not have processed point on the curve, carries out bending identification once more, marks off the bending of next level, then according to the mode of description in the step 2 abbreviation once more.
Step 4: repeat above-mentioned abbreviation process, all processed until all data points, finished whole abbreviation process.
Four, improve the implementation procedure of Douglas-Peucker algorithm
Among the present invention in design Douglas-Peucker abbreviation algorithm implementation procedure, if in the middle of finding not write down apart from maximum vertex, can cause the repeatedly judgement of individual data in cyclic process, increased the time complexity that algorithm is realized.In order to overcome this problem, will judge that in the algorithm for design implementation procedure the middle ultimate range summit of gained is preserved, operand that like this can less algorithm improves algorithm efficiency.In addition, the needs according to electronic chart vector graph is simplified increase the restriction of curved width in Douglas-Peucker abbreviation algorithm implementation procedure, be about to the curve width and be used to limit curve abbreviation result as a threshold value.The improvement algorithm implementation procedure that satisfies above 2 requirements is described below:
(1) establishes vector curve by discrete point range (p
0, p
1..., p
n) expression, with array T storage feature point range, with starting point p
0With end point p
nDeposit first place and the end of T in order in, make A ← p
0, B ← p
n, connect AB;
(2) whether judge distance between the line segment AB greater than given width threshold value, if not, change (4), if, seek the point that has ultimate range with line segment AB in the point range between AB, if there is the point that satisfies condition, then change (3), otherwise change (5);
(3) whether judge this distance of putting line segment AB greater than given height threshold, if establishing this point is C, and deposits in proper order among the T by it, makes B ← C, returns (2);
(4) seek the point that has ultimate range with line segment AB in the point range between AB, if this distance of putting line segment AB greater than given height threshold and this in the left side of directed line segment AB, establishing this point is C, and deposits in proper order among the T by it, makes B ← C, returns (2);
(5) judge whether B is p
n, if not, making A ← B, B ← T ' (the next unique point of T) connects AB, returns (2);
(6) A, B are deposited in the feature point range, finish.
According to the embodiment of above elaboration, the data of extracting figure number and be Hai Tan island in the electronic chart of C10015 are shown in Fig. 4 A.These island are described by 534 discrete original vector data points.Dotted line is the convex hull on these island among Fig. 4 B.Choose different depth threshold and width threshold value the abbreviation operation is carried out on these island, the result is shown in Fig. 4 C-4F.
The different abbreviation threshold values of the table 1 altar island abbreviation statistical form as a result of plunging into the commercial sea
For illustrating further the validity and the practicality of the simplifying method of electronic chart vector graph that the present invention proposes, in dominant frequency is 2.8GHz, in save as on the robot calculator of 4G, choose engineer's scale and be 1: 100 ten thousand C10013 sea chart and carry out full figure island data abbreviation under the different threshold values, abbreviation the results are shown in Table 2.These figure island abbreviation result's part figure when Fig. 5 is chosen for 1km and 1.5km respectively for depth threshold and width threshold value.
Abbreviation statistical form as a result in C10013 sea chart full figure island under the different abbreviation threshold values of table 2
Effect analysis: anatomize in the table 2 the abbreviation result data as can be seen, the threshold value of choosing when the ratio of island data point abbreviation and abbreviation is closely related.Selection of threshold big more, what data point kept behind the abbreviation is few more, and the abbreviation rate is high more, but the conformality on island is also poor more.Therefore, in actual applications, should by a large amount of analysis of experimentss, determine to satisfy the appropriate threshold value of application conditions in conjunction with concrete condition according to different application demands.Can see clearly from Fig. 5, the simplifying method of electronic chart vector graph of using the present invention's proposition carries out the vector graphics abbreviation, the basic geometric shape that can effectively guarantee vector graphics is constant, and the geometric figure spatial topotaxy behind the abbreviation is preceding consistent with abbreviation.And the method for using the present invention's proposition is carried out the possibility that the vector graphics abbreviation can effectively avoid the abbreviation result self intersection to occur and hand over mutually.
Claims (4)
1. simplifying method of electronic chart vector graph is characterized in that:
(1) extracts the convex hull of given vector graphics;
(2) will handle by figure protuberance and recess classification that convex hull marks off, carry out abbreviation respectively;
(3) directly use the Douglas-Peucker algorithm figure protuberance is carried out abbreviation; The figure recess adopts successively the method for abbreviation to carry out abbreviation, for the recess that has complicated bend, application identifies the bending of different levels based on the crooked recognition methods of straight-line segment moving direction, then abbreviation is carried out in the bending of each level respectively, finishes until all bending processes;
(4), increase an abbreviation threshold value, implement abbreviation to recess.
2. simplifying method of electronic chart vector graph according to claim 1 is characterized in that the method for the convex hull of the vector graphics that described extraction is given comprises:
Step 1: for given polygon, find out the point of ordinate minimum in all data points, be designated as p
1, from p
1Beginning polygon oriented vertex sequence along clockwise direction is (p
1, p
2..., p
n);
Step 2: search convex hull summit: note p
1Be the summit on first convex hull, then from directed line segment p
1p
2Begin to search, if polygonal all summits are all at directed line segment p
1p
2The right side, p then
2Also be the convex hull summit, otherwise search directed line segment p in turn
1p
3, p
1p
4..., satisfy polygonal all summits all at p until finding
1p
iThe some p on right side
i, then remember p
iBe the convex hull summit, then from p
iBeginning is according to above-mentioned and p
1Begin same step and search the convex hull summit in turn, up to returning p
1Till the point, write down all convex hull summits successively, and line has just been finished the generative process of polygon convex hull in turn.
3. simplifying method of electronic chart vector graph according to claim 2 is characterized in that the method that described figure recess adopts the method for abbreviation successively to carry out abbreviation comprises:
Step 1: carry out bending for given recess curve and divide, identify the bending of first level;
Step 2: whether judge crooked number greater than 1, if not, then the bending of this curve composition is a simple bending, directly abbreviation; Otherwise, carry out abbreviation respectively for each bending, and whether the process information that writes down each data point keeps behind abbreviation promptly;
Step 3: behind the crooked abbreviation of first level, traversal does not have processed point on the curve, carries out bending identification once more, marks off the bending of next level, then according to the mode of description in the step 2 abbreviation once more;
Step 4: the abbreviation process of repeating step 1-3, all processed until all data points, finished whole abbreviation process.
4. simplifying method of electronic chart vector graph according to claim 3 is characterized in that described Douglas-Peucker algorithm for improving algorithm, and it realizes that process prescription is as follows:
1) establishes vector curve by discrete point range (p
0, p
1..., p
n) expression, with array T storage feature point range, with starting point p
0With end point p
nDeposit first place and the end of T in order in, make A ← p
0, B ← p
n, connect AB;
2) whether judge distance between the line segment AB greater than given width threshold value, if not, change 4), if, seek the point that has ultimate range with line segment AB in the point range between AB, if there is the point that satisfies condition, then change 3), otherwise change 5);
3) whether judge this distance of putting line segment AB greater than given height threshold, if establishing this point is C, and deposits in proper order among the T by it, makes B ← C, returns 2);
4) seek the point that has ultimate range with line segment AB in the point range between AB, if this distance of putting line segment AB greater than given height threshold and this in the left side of directed line segment AB, establishing this point is C, and deposits in proper order among the T by it, makes B ← C, returns 2);
5) judge whether B is p
n, if not, make A ← B, B ← T ' connects AB, returns 2);
6) A, B are deposited in the feature point range, finish.
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| CN104537635A (en) * | 2014-09-29 | 2015-04-22 | 中国科学院遥感与数字地球研究所 | Simplification algorithm for land cover vector data for maintaining topology |
| CN104978763A (en) * | 2015-05-13 | 2015-10-14 | 中国矿业大学(北京) | Three-dimensional Douglas-Peucker algorithm based map simulation method for synchronous integration of river network elements and DEM |
| CN105787977A (en) * | 2016-02-26 | 2016-07-20 | 民政部国家减灾中心 | Building vector boundary simplification method |
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| CN104978763A (en) * | 2015-05-13 | 2015-10-14 | 中国矿业大学(北京) | Three-dimensional Douglas-Peucker algorithm based map simulation method for synchronous integration of river network elements and DEM |
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