CN105741331B - SAR image Geocoding based on irregular triangle network look-up table - Google Patents
SAR image Geocoding based on irregular triangle network look-up table Download PDFInfo
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- CN105741331B CN105741331B CN201610069176.1A CN201610069176A CN105741331B CN 105741331 B CN105741331 B CN 105741331B CN 201610069176 A CN201610069176 A CN 201610069176A CN 105741331 B CN105741331 B CN 105741331B
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- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T9/00—Image coding
- G06T9/007—Transform coding, e.g. discrete cosine transform
Abstract
The invention discloses one kind to be based on irregular triangle network (Triangulated Irregular Network, TIN) the Geocoding of the SAR image of look-up table, comprising: the Grid dem data conversion of SAR image overlay area is generated into TIN dem data；According to SAR image information, the mapping relations of TIN DEM each node and SAR image radar fix are obtained by calculation, are stored in TIN look-up table；According to the mapping relations in SAR image information and look-up table, resampling, the SAR image after obtaining geocoding are carried out.The present invention is based on TIN look-up tables, only TIN node is carried out mapping relations are calculated, other grid points obtain mapping relations using interpolation, thus storage and calculation amount are reduced, the deficiencies of data redundancy, inefficiency existing for the existing Geocoding using Grid look-up table can be overcome, is suitable for carrying out fast and efficiently geocoding for a large amount of SAR images in areal.
Description
Technical field
The present invention relates to synthetic aperture radar (Synthetic Aperture Radar, SAR) image geocodings, especially
With being related to SAR image of the one kind based on irregular triangle network (Triangulated Irregular Network, TIN) look-up table
Manage coding method.
Background technique
Diameter radar image is widely used in the fields such as mapping, geological mapping, environmental monitoring and Disaster Assessment.
SAR image is unfavorable for the extraction of thematic geography information and the comparative analysis with other geography information with the storage of radar fix system；Separately
Outside, the characteristics of SAR image is imaged because of its side view, influences vulnerable to conformation geometry, hypsography etc. and generates geometric distortion, such as before
Depending on shrinking, folded cover with shade etc..
The purpose of SAR image geocoding is that the mapping established between the radar fix system of image and geographic coordinate system is closed
System eliminates geometric distortion, and convenient for matching with other geography information, look-up table is that expression stores one kind of this mapping relations often
Data structure.Traditional look-up table and DEM has consistent geographic coordinate system, suitable with the row, column of regular grid (Grid)
Sequence stores coordinate mapping relations by pixel.And Grid look-up table the characteristics of not accounting for topography variation, to there is a large amount of number
According to redundancy.For example, mapping relations can be expressed using less grid points in flat Plain relative to steep hills area, and
Geographical encoding precision will not be caused to significantly affect.In addition, each grid points of Grid look-up table require to calculate mapping relations, therefore
Memory space and calculating time overhead are all larger.As SAR technology develops, SAR image quantity is continuously increased, and areal may
There are different a large amount of SAR images such as SAR platform, polarization, phase, observation angle, and utilize existing based on Grid look-up table
Geocoding handles these SAR images, needs to calculate mapping relations by pixel every time for different SAR images, it is difficult to
Meet fast and efficiently processing requirement.
Summary of the invention
In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a kind of based on irregular triangle network
The Geocoding of the SAR image of (Triangulated Irregular Network, TIN) look-up table can overcome existing
There is the deficiencies of data redundancy, inefficiency existing for the Geocoding using Grid look-up table, is suitable for for samely
The a large amount of SAR images in area carry out fast and efficiently geocoding.
Present invention provide the technical scheme that
One kind is schemed based on the SAR of irregular triangle network (Triangulated Irregular Network, TIN) look-up table
The Geocoding of picture, comprising the following steps:
1) the Grid dem data of SAR image overlay area is converted, generates TIN dem data；
2) according to SAR image information, the mapping relations of TIN DEM each node and SAR image radar fix, storage are calculated
In TIN look-up table；
3) according to the mapping relations in SAR image information and look-up table, resampling, the SAR after obtaining geocoding are carried out
Image.
In resampling steps, the present invention uses TIN look-up table, mapping relations only is calculated to TIN node, to not existing
Other grid points on node then obtain mapping relations using interpolation.Specifically, if the image picture elements (x, y) are not searched in TIN
On table node, then (i, j) is obtained by the node index value of triangular facet where the linear interpolation pixel.Since interpolation calculation is very simple
It is single, mapping relations are strictly calculated compared to according to SAR conformation model, interpolation calculation expense can be ignored substantially.Therefore, the present invention mentions
The method of confession can reduce storage, reduce calculation amount.
For the Geocoding of the above-mentioned SAR image based on TIN look-up table, further, the step 1) conversion
An elevation tolerance limit is set first, and the elevation tolerance is limited the use of in the structure and TIN DEM and Grid of control TIN DEM
The degree of approximation of DEM；Geocoding is carried out based on TIN look-up table, can be reduced the memory space of look-up table occupancy, and elevation tolerance
Limit is bigger, and memory space is smaller；In addition, the step 1) conversion only needs to carry out when handling several identical regional SAR images
Once；
For the Geocoding of the above-mentioned SAR image based on TIN look-up table, further, the step 1) generation
In the structure of TIN dem data, for all nodes under geographic coordinate system, each node data field is the corresponding SAR of the node
Image radar fix, the radar fix include that distance is indexed to index and orientation.
For the Geocoding of the above-mentioned SAR image based on TIN look-up table, further, the step 2) calculating
With specific reference to SAR image information, calculated by range Doppler model；In embodiments of the present invention, how general the distance is
Model is strangled to be made of ellipsoid equation or plane equation (formula 1), oblique distance equation (formula 2), Doppler equation (formula 3):
In 1~formula of formula 3,For ground point location vector；ReFor earth ellipsoid major semiaxis；RpFor earth ellipsoid
Semi-minor axis；H is ground point geodetic height；For SAR platform position vector；R is SAR platform and ground point oblique distance
Length；For SAR platform velocity vector；For ground point velocity vector；λ is radar wavelength；fdFor doppler centroid.SAR
Any pixel of image can obtain unique SAR platform position vector and oblique distance when its imaging according to SAR image information, utilize distance
Its geographical location information can be calculated in Doppler model and TIN DEM elevation information.SAR image information describes SAR image
Parameter mainly includes SAR platform location information, velocity information, oblique distance information, imaging time information, imaging parameters information etc..
Above-mentioned steps 2) method therefor compared to conventional method can effectively reduce runing time.When the image of processing increases,
When such as a large amount of SAR image geocodings in areal, since step 1) only need to be into when handling several identical regional images
Row is primary；When therefore, the time required to the time of step 2) reduction is greater than step 1), the calculating time of the method for the present invention is reduced,
Method is high-efficient.
For the Geocoding of the above-mentioned SAR image based on TIN look-up table, further, the step 2) TIN is looked into
Look for the TIN topological structure of table identical as the TIN topological structure of TIN DEM that step 1) generates, the TIN data field of TIN look-up table
It is indexed for the distance of SAR image to index and orientation.
For the Geocoding of the above-mentioned SAR image based on TIN look-up table, further, step 3) is described heavy to be adopted
Sample first determine output image range and output pixel size, then according to the mapping relations in TIN look-up table, treat into
The SAR image of row geocoding carries out resampling, the SAR image after obtaining geocoding.
For the Geocoding of the above-mentioned SAR image based on TIN look-up table, further, the pending geography
The SAR image of coding is original SAR image processing result of the original SAR image either under same radar fix system.When to
The geographical coordinate of the SAR image pixel point of geocoding is carried out not when on TIN node, by where the linear interpolation pixel point
The index value of the node of triangular facet obtains the index value of the pixel point, thus obtains image radar fix value.
Compared with prior art, the beneficial effects of the present invention are:
The present invention provide it is a kind of new based on irregular triangle network (Triangulated Irregular Network,
TIN) the Geocoding of the SAR image of look-up table can overcome the shortcomings of the existing method based on Grid look-up table, be applicable in
In carrying out fast and efficiently geocoding for a large amount of SAR images in areal, be not only suitable for it is spaceborne be equally applicable to it is airborne
SAR image geocoding.Technical solution of the present invention has the advantage that
(1) in terms of memory space, relative to Grid look-up table, the present invention can be reduced the memory space of look-up table occupancy,
And the elevation tolerance limit of setting is bigger, memory space is smaller；
(2) at runtime between aspect, although step 1) needs certain runing time, for areal multiple image
For, step 1) only needs to carry out primary.In addition, step 2) effectively subtracts compared to the method runing time based on Grid look-up table
It is few, therefore SAR image geocoding a large amount of for areal, the present invention can be reduced its runing time.
Detailed description of the invention
Fig. 1 is the flow diagram of the SAR image Geocoding provided by the invention based on TIN look-up table.
Fig. 2 is to indicate that TIN look-up table describes between geographic coordinate system and SAR image radar fix system in the embodiment of the present invention
The schematic diagram of mapping relations；
Wherein, (a) is TIN look-up table configuration；It (b) is SAR image radar fix system；TIN look-up table and DEM have consistent
Geographic coordinate system, X indicate geographic coordinate system under the north to；Y indicate geographic coordinate system under east to；(i, j) indicates picture
The distance of the corresponding SAR image radar fix system of member is indexed to orientation pixel.
Specific embodiment
With reference to the accompanying drawing, the present invention, the model of but do not limit the invention in any way are further described by embodiment
It encloses.
The present invention provide it is a kind of new based on irregular triangle network (Triangulated Irregular Network,
TIN) the Geocoding of the SAR image of look-up table can overcome the shortcomings of the existing method based on Grid look-up table, be applicable in
Fast and efficiently geocoding is carried out in being directed to a large amount of SAR images in areal.Fig. 1 is the SAR image based on TIN look-up table
The flow diagram of Geocoding, in the present embodiment, the method for the present invention is implemented specific to execute following steps:
1) it is limited according to a preset elevation tolerance, SAR image overlay area Grid DEM is converted into TIN
DEM.Its process converted is summarized as follows: inputting the geographical coordinate of tetra- boundary points of Grid DEM first, DEM is divided into two
Triangular facet, then selects one of triangular facet, and calculating falls into the triangular facet all grid points of DEM to the elevation of the triangular facet
Difference, judges whether highest elevation difference is greater than elevation tolerance limit, DEM grid points is then inserted into if more than elevation tolerance limit, by triangular facet
Several small triangular facets of subdivision, successively judge newly-generated triangular facet, until grid point height in all triangular facets and are somebody's turn to do
The depth displacement of triangular facet is limited less than elevation tolerance, stops recurrence.When handling several SAR images of areal, which is only needed
It carries out primary.
2) it is corresponding to be calculated using range Doppler model according to SAR image information and TIN DEM for each node of TIN DEM
SAR image radar fix (distance is indexed to index and orientation), and calculated result is stored in TIN look-up table.Fig. 2 is indicated
TIN look-up table describes the mapping relations between geographic coordinate system and SAR image radar fix system.The TIN topology of TIN look-up table
The TIN topological structure of structure TIN DEM corresponding to generation be it is identical, the TIN data field of TIN look-up table is SAR image
Distance is indexed to index and orientation.It is, both TIN look-up table and corresponding TIN DEM have identical quantity and position
Node, triangular facet is also identical；Under geographic coordinate system, each node data field is corresponding for the node for its all node processing
SAR image radar fix (distance is indexed to orientation).
Wherein, range Doppler model is by ellipsoid equation or plane equation (formula 1), oblique distance equation (formula 2), Doppler equation
(formula 3) composition:
In 1~formula of formula 3,For ground point location vector；ReFor earth ellipsoid major semiaxis；RpFor earth ellipsoid
Semi-minor axis；H is ground point geodetic height；For SAR platform position vector；R is that SAR platform and ground point oblique distance are long
Degree；For SAR platform velocity vector；For ground point velocity vector；λ is radar wavelength；fdFor doppler centroid.SAR figure
Unique SAR platform position vector and oblique distance when can obtain its imaging according to SAR image information as any pixel are more using distance
Its geographical location information can be calculated in general Le model and TIN DEM elevation information.
(3) resampling
According to the mapping relations in SAR image information and look-up table, resampling is carried out；Wherein, SAR image information includes
SAR image distance is to pixel quantity and orientation pixel quantity.Carry out resampling when, when look-up table index be greater than distance to,
Orientation pixel quantity or when less than 0, is set to null value for the pixel.
The process for carrying out resampling is as follows:
Firstly, determining that the geographic range and Pixel domain size of image after the geocoding exported (can be with initial Grid
DEM is consistent), then geographical encoded images pixel (x, y) is selected to search the pixel according to TIN look-up table and correspond to SAR one by one
The distance of image indexes (i, j) to orientation pixel.If the image picture elements (x, y) not on TIN look-up table node, (i,
J) it is obtained by the node index value of triangular facet where the linear interpolation pixel.Here SAR image is for original SAR image or same
Other SAR image processing results under one radar fix system.Scheme after assigning SAR image (i, j) pixel gray value to geocoding
As pixel (x, y).If (i, j) does not index for integer pixel, which is obtained by interpolation；If (i, j) is greater than SAR
Image picture elements (x, y) after geocoding are then set to null value by image range.
It should be noted that the purpose for publicizing and implementing example is to help to further understand the present invention, but the skill of this field
Art personnel, which are understood that, not to be departed from the present invention and spirit and scope of the appended claims, and various substitutions and modifications are all
It is possible.Therefore, the present invention should not be limited to embodiment disclosure of that, and the scope of protection of present invention is with claim
Subject to the range that book defines.
Claims (9)
1. a kind of Geocoding of the SAR image based on TIN look-up table, comprising the following steps:
1) the Grid dem data of SAR image overlay area is converted, generates TIN dem data；
2) according to the SAR image information, the mapping of TIN DEM each node and SAR image radar fix is obtained by calculation
Relationship is stored in TIN look-up table；
3) according to the mapping relations in the SAR image information and the TIN look-up table, resampling is carried out, geocoding is obtained
SAR image afterwards.
2. the Geocoding of the SAR image as described in claim 1 based on TIN look-up table, characterized in that step 1) is described
Conversion sets elevation tolerance limit first, the elevation tolerance limit the use of in control TIN DEM structure and TIN DEM with
The degree of approximation of Grid DEM；When handling several identical regional SAR images, the step 1) conversion only needs to carry out primary.
3. the Geocoding of the SAR image as described in claim 1 based on TIN look-up table, characterized in that step 1) is described
In the structure for generating TIN dem data, for all nodes under geographic coordinate system, each node data field is that the node is corresponding
SAR image radar fix, the radar fix include that distance is indexed to index and orientation.
4. the Geocoding of the SAR image as described in claim 1 based on TIN look-up table, characterized in that step 2) is described
Calculating is calculated especially by range Doppler model；The ellipsoid equation or put down that the range Doppler model is indicated by formula 1
The Doppler equation composition of oblique distance equation, the expression of formula 3 that face equation, formula 2 indicate:
In 1~formula of formula 3,For ground point location vector；ReFor earth ellipsoid major semiaxis；RpIt is short by half for earth ellipsoid
Axis；H is ground point geodetic height；For SAR platform position vector；R is SAR platform and ground point oblique distance length；For SAR platform velocity vector；For ground point velocity vector；λ is radar wavelength；fdFor doppler centroid.
5. the Geocoding of the SAR image as described in claim 1 based on TIN look-up table, characterized in that step 2) is described
The data structure of TIN look-up table is identical as the structure of TIN dem data that step 1) generates.
6. the Geocoding of the SAR image as described in claim 1 based on TIN look-up table, characterized in that step 3) is described
Resampling determines the image range of output and the size of output pixel first, right then according to the mapping relations in TIN look-up table
The SAR image of pending geocoding carries out resampling, the SAR image after obtaining geocoding.
7. the Geocoding of the SAR image as claimed in claim 6 based on TIN look-up table, characterized in that described pending
The SAR image of geocoding is original SAR image processing result of the original SAR image either under same radar fix system.
8. the Geocoding of the SAR image as claimed in claim 7 based on TIN look-up table, characterized in that for it is described to
The SAR image for carrying out geocoding carries out resampling, when the geographical coordinate of the SAR image pixel point of pending geocoding does not exist
When on TIN node, the index value of the pixel point is obtained by the index value of the node of triangular facet where the linear interpolation pixel point,
Thus image radar fix value is obtained.
9. the Geocoding of the SAR image as described in claim 1 based on TIN look-up table, characterized in that the SAR figure
As information describes SAR image parameter；When the SAR image parameter includes SAR platform position, SAR platform speed, oblique distance, imaging
Between and one or more of imaging parameters.
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| CN102521884A (en) * | 2011-12-16 | 2012-06-27 | 南京大学 | Three-dimensional roof reconstruction method based on LiDAR data and ortho images |
| CN102520406A (en) * | 2011-12-20 | 2012-06-27 | 中国测绘科学研究院 | SAR (synthetic aperture radar) stereoscopic model construction and measurement method based on image coordinate mapping |
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