CN102737357B - Method for generating simulation data of lunar three-linear array camera images - Google Patents

Abstract

The invention discloses a method for generating simulation data of lunar three-linear array camera images. The method comprises: step 1, that orbit data of a lunar satellite is simulated, wherein orbit parameters comprise an orbit height, an orbit inclination angle, and an eccentricity; step 2, that attitude data of the lunar satellite is simulated; step 3, that according to the orbit data and the attitude data of the satellite, positions of projective points in a digital elevation model are acquired through a projection-back-projection manner, wherein the projective points are the projective points of projection beams respectively corresponding to pixels of a three-liner array camera; and step 4,that pixel tonal value is acquired. In the invention, data of the digital elevation model which utilizes orthoimages and corresponds the same area of lunar surface is provided, design parameters of the lunar three-linear array camera, design parameters of the satellite orbit and the like are combined, and the lunar three-linear camera images are simulated according to operational principles of three-linear array cameras and the projection-back-projection method which is commonly used in satellite photographic measurement, thereby providing simulation data sources for further researches of lunar three-linear camera image data.

Description

The generation method of the moon three line-scan digital camera image simulation data

Technical field

The present invention relates to image processing field, particularly a kind of to take positive photograph picture and digital elevation model be basis, and emulation generates lunar orbiter three-linear array CCD stereoscopic camera forward sight, face the method with backsight moon three-line imagery data.

Background technology

Three line-scan digital cameras are one and only have the area array cameras that one group of optical lens, detector size are 1024 * 1024, in face battle array, read edge perpendicular to the 11st row on heading, the 512nd row and the 1013rd row, respectively as forward sight, face the array imaging with three different visual angles of backsight, the pixel count of every line battle array is 512 row, forward sight, face subtense angle between linear array adjacent with backsight and be 16.7 °, imaging spectral coverage is the visible light wave range of 0.5 μ m～0.75 μ m.The in-orbit flight parameter predetermined according to satellite, the sweep velocity of camera was made as for 11.89 frame/seconds, to guarantee that satellite three linear arrays lunar surface that three directions can be flown over satellite with the three width bidimensional image bands that push away the mode of sweeping and obtain forward, downwards and backward on the high track of 200km carries out 100% imaging simultaneously.Article three, image strip almost obtains simultaneously, fabric width is 60km, satellite flight direction have 100% overlapping, under the line near the degree of overlapping of adjacent orbit image strip be about 41%, high latitude area degree of overlapping is larger, for the geometrical reconstruction of menology dimensional topography provides enough image informations.Fig. 2 is exemplified with " Chang'e I (CE-1) " detector C CD stereoscopic camera menology three-line imagery data acquisition schematic diagram.

For example, before lunar exploration satellite (" Chang'e I (CE-1) ") transmitting, carry out a large amount of research work, but according to prior art, the needed data source of research work, for example obtaining of the emulated data of the moon three line-scan digital camera images is a great problem, owing to being subject to the restriction of data source factor, cannot carrying out the experimental work in later stage, thereby make the correctness of the principle of proposition and the three-line imagery disposal route of employing can not get effective checking.

Summary of the invention

In order to solve the above-mentioned defect of prior art, the invention provides that a kind of to take positive photograph picture and digital elevation model be basis, emulation generates lunar orbiter three-linear array CCD stereoscopic camera forward sight, face the method with backsight moon three-line imagery data.

The method comprising the steps of: step 1, and emulation lunar exploration satellite orbit data, orbit parameter comprises orbit altitude, orbit inclination and excentricity; Step 2: emulation lunar exploration attitude of satellite data; Step 3: according to satellite orbit and attitude data, utilize the mode of projection-back projection to obtain the subpoint position of projected light beam corresponding to each pixel of three line-scan digital cameras on digital elevation model; Step 4, obtains grey scale pixel value.

Preferably, above-mentioned steps 3 further comprises: step 301, set up camera imaging model, and build the measurement vector of each pixel; Step 302, is transformed into a month solid coordinate by measurement vector from image coordinate; Step 303, solves the intersection point of the moonscape that measurement vector and Law of DEM Data express.

Preferably, above-mentioned steps 3 further comprises: the method iterative measurement vector and this surperficial intersection point that adopt projection-back projection.

Preferably, above-mentioned steps 3 further comprises: the first step, solves the intersection point A of the positive spheroid table of measurement vector and the moon; Second step, is converted to latitude and longitude coordinates and height value by a month solid three-dimensional rectangular coordinate of intersection point A, then on Law of DEM Data, inquires about the spot elevation B that this longitude and latitude is corresponding; The 3rd step, calculate the distance that B point and A are ordered | AB|; The 4th step, if distance value | AB| can not meet the demands, and the vertical line of crossing the B Dian Zuo OA of projection ray obtains intersection point point C, then on Law of DEM Data, inquires about the spot elevation D that this longitude and latitude is corresponding; The 5th step, calculate the distance that D point and C are ordered | DC|; Repeat the 4th step～five step, until the distance value in the 5th step meets the demands, iterative computation finishes, and obtains the intersecting point coordinate of projected light beam and digital elevation model.

Preferably, step 4 further comprises: according to position of intersecting point, adopt bilinear interpolation algorithm to obtain the grey scale pixel value of the corresponding simulating image of this measurement vector from orthography data.

The present invention proposes the Law of DEM Data (for example Apollo Law of DEM Data) that utilizes orthography (Clemtine BaseMap) and corresponding identical lunar surface region, in conjunction with the design parameter of the moon three line-scan digital cameras, Orbit Design parameter etc., according to projection-back projection method conventional in the principle of work of three line-scan digital cameras and satellite photogrammetry, carry out the moon three line-scan digital camera image simulations, for the further research of the moon three line-scan digital camera image datas provides simulation data source.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of the generation method of the moon three line-scan digital camera image simulation data of the present invention;

Fig. 2 is lunar exploration Satellite CCD stereoscopic camera menology three-line imagery data acquisition schematic diagram;

Fig. 3 is three-dimensional Descartes's image coordinate and two-dimensional pixel coordinate schematic diagram;

Tu4Wei projection ray and DEM intersection point derivation algorithm schematic diagram;

Tu5Wei emulation experiment district dem data (Apollo dem data) schematic diagram;

Tu6Wei emulation experiment district orthography data (Clementine BaseMap) schematic diagram;

Fig. 7 is the moon three linear array simulating image schematic diagram, is followed successively by forward sight from top to bottom, faces, rear view.

Embodiment

For making the object, technical solutions and advantages of the present invention clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, the present invention is described in more detail.

Fig. 1 is the process flow diagram of the generation method of the moon three line-scan digital camera image simulation data of the present invention, specifically comprises the following steps.

In step 1, emulation lunar exploration satellite orbit data.The orbit parameter of lunar exploration satellite comprises orbit altitude, orbit inclination and excentricity.

It is example that " Chang'e I (CE-1) " detector is take in the present invention, is surveyed nominal track and is defined as: orbit altitude: 200km, orbit inclination: 90 ± 5 degree, excentricity: positive circuit orbit, excentricity is 0.

According to above-mentioned nominal orbit parameter, utilizing the emulation of satellite orbit simulation software to generate Chang'e I satellite orbit data.

In step 2, emulation lunar exploration attitude of satellite data.Or " Chang'e I " detector of take is example, rule of thumb formula emulation Chang'e I detector attitude data.

In step 3, utilize the mode of projection-back projection to calculate the subpoint position of projected light beam corresponding to each pixel on digital elevation model.

Projection-back projection method is orthography and the Law of DEM Data that utilizes survey region, first based on projection equation, solve the digital elevation model subpoint corresponding with pixel, then by subpoint coordinate back projection a kind of image simulation method to existing image capturing grey scale pixel value.

According to the three-linear array CCD stereoscopic camera principle of work of introducing in background technology, forward sight, face with backsight linear array and all have 512 pixels, in any one imaging constantly, the projected position of ray from projection centre to pixel on lunar surface, be the image space of this pixel of this moment on lunar surface, that is along this directions of rays, be transferred to this pixel at the energy of the moon of this this projected position of moment Area Objects reflection sun, by this pixel, be recorded as the gray-scale value of view data.The algorithm of projection-back projection is followed this imaging process, first according to projection centre, location of pixels, build measurement vector, then calculating observation vector and the truly intersection point of menology (true menology is expressed with digital elevation model here), then according to this position of intersecting point, from existing menology view data (adopting orthography data here), obtain image greyscale value, as the gray-scale value of this pixel.

Provide the data handling procedure of this algorithm below, further comprised step:

In step 301, set up camera imaging model, build the measurement vector of each pixel.

Setting up camera imaging model fundamental purpose is to set up the measurement vector of each pixel under image coordinate system.

Fig. 6 is the schematic diagram of three-dimensional Descartes's image coordinate and two-dimensional pixel coordinate.This image coordinate system is for expressing the volume coordinate of image space.The initial point of this coordinate system is positioned at projection centre, and positive z axle is contrary with optical axis direction, x, and y plane and picture plane parallel, positive x direction of principal axis is along heading, and heading is perpendicular to image scan line.Pixel coordinate system is the reference frame of digital picture.Principal point PP is projection centre O vertical projection position in picture plane; It as plane datum points FC, is the center of picture plane; Upper left point position M is the origin position of pixel coordinate system.Interior orientation element comprises (in Table 1) such as principal point position, camera focus and solid angles in picture plane.

Table 1 camera main geometric parameters

Position in image space can be expressed with vector.Picture point P _f, P _nand P _bbe respectively forward sight, face with backsight image on picture point.Vector with defined respectively the picture point P under pixel coordinate system _f, P _nand P _bposition under image coordinate system.Picture point P _f, P _nand P _bpixel coordinate by row and the scan line of digital picture, defined, be respectively with

Referring to Fig. 6, according to the image-forming principle of CCD stereoscopic camera, obviously the image coordinate of picture point only with the scan line c of pixel coordinate _prelevant with elements of interior orientation.We can utilize formula below by picture point P _f, P _nand P _bpixel coordinate be converted to image coordinate.

Front view picture:

$\stackrel{\→}{p_f}=\left[\begin{array}{c}{x}_{P_f}\\ y_{P_f}\\ z_{P_f}\end{array}\right]=\left[\begin{array}{c}f\×\tan \left(\mathrm{\α}\right)-x_0\\ (c_{P_f}-c_0)\×\mathrm{ps}-y_0\\ -f\end{array}\right]---\left(1a\right)$

Front elevation picture:

$\stackrel{\→}{p_n}=\left[\begin{array}{c}{x}_{P_n}\\ y_{P_n}\\ z_{P_n}\end{array}\right]=\left[\begin{array}{c}-x_0\\ (c_{P_n}-c_0)\×{\mathrm{ps}-y}_0\\ -f\end{array}\right]---\left(1b\right)$

Rear view picture:

$\stackrel{\→}{p_b}=\left[\begin{array}{c}{x}_{P_b}\\ y_{P_b}\\ z_{P_b}\end{array}\right]=\left[\begin{array}{c}f\×\tan (-\mathrm{\α})-x_0\\ (c_{P_b}-c_0)\×\mathrm{ps}-y_0\\ -f\end{array}\right]---\left(1c\right)$

In formula, ps is three line-scan digital camera detector pixel sizes, be respectively picture point P _f, P _n, P _bimage coordinate, α=16.7 ° are the solid angle of camera, i.e. forward sight and face or face the angle between backsight, represent picture point P _f, P _n, P _bforward sight, face with backsight linear array on column position, x ₀=0.8050, y ₀=-0.7990, (x ₀, y ₀) be the picture planimetric coordinates value of principal point, unit is pixel.

In step 302, by measurement vector with from image coordinate, be transformed into a month solid coordinate.

Because positive photograph is all that coordinate system is undefined admittedly in the moon as data and Law of DEM Data, in order to adopt projection-Inverse Projection to solve the intersection point of the moonscape of measurement vector and Law of DEM Data expression, measurement vector must be transformed into a month solid coordinate from image coordinate, coordinate conversion will be used emulation satellite orbit data and attitude data.Carrying out coordinate conversion is technology well known in the art, does not repeat them here.

In step 303, solve the intersection point of the moonscape of measurement vector and Law of DEM Data expression.

The moonscape that Law of DEM Data is expressed is moon natural surface, very complicated, cannot express by the funtcional relationship showing, therefore cannot be by resolving method direct solution measurement vector and this surperficial intersection point of equation.Here adopt method iterative measurement vector and this surperficial intersection point of projection-back projection, key step is as follows: the first step, solving measurement vector and radius is the intersection point A of the positive spheroid table of the moon of 1737.4 kilometers, and to be wherein 1737.4 kilometers be the moon standard radius that Union Astronomique Internationale is recommended to radius; Second step, consolidates a three-dimensional rectangular coordinate (X, Y, Z) by the moon of A and is converted to latitude and longitude coordinates and height value, then on Law of DEM Data, inquires about the spot elevation B that this longitude and latitude is corresponding; The 3rd step, calculate the distance that B point and A are ordered | AB|; The 4th step, if distance value | AB| can not meet the demands, for example | AB| < 0.01, the vertical line of crossing the B Dian Zuo OA of projection ray obtains intersection point point C, then on Law of DEM Data, inquires about the spot elevation D that this longitude and latitude is corresponding; The 5th step, calculate the distance that D point and C are ordered | DC|; Repeat four step-, five steps, until the distance value in the 5th step meets the demands, iterative computation finishes, and obtains the intersecting point coordinate of projected light beam and digital elevation model.

Step above can be understood with reference to Fig. 6.Tu6Shi projection ray and menology digital elevation model surface intersection point derivation algorithm schematic diagram.Starting point is A, and namely projection ray and radius are the intersection point of 1737.4 kilometers of positive spherome surfaces.The three-dimensional coordinate of ordering according to A can calculate its latitude and longitude coordinates, then on Law of DEM Data, inquires about the height value that this longitude and latitude is corresponding, namely inquires the coordinate that B is ordered, the distance that relatively A point and B are ordered.If can not meet the demands, (the two obtains the intersection point on projected light beam and DEM surface while overlapping, in fact can not overlap completely, when the two distance L EssT.LTssT.LT 0.01m, think and meet the demands), the vertical line of crossing the B Dian Zuo OA of projection ray obtains intersection point point C, the latitude and longitude coordinates inquiry DEM point D of ordering according to C, compare C point and D point distance, if can not meet the demands, sequential iteration obtains E point and F point, G point and H are ordered etc. successively, while meeting the demands, iterative computation finishes to exit, and obtains the intersecting point coordinate of projected light beam and DEM.

In step 4, according to the intersecting point coordinate of elevation model interpolation orthography data, obtain image greyscale data as the gray-scale value of three-line imagery data.

Here the geographic range of orthography, map projection's mode are identical with digital elevation model, what in step 3, obtain is a month solid three-dimensional rectangular coordinate, through coordinate conversion, can obtain the planimetric rectangular coordinates of map projection pattern identical with orthography, then according to this planimetric rectangular coordinates, according to following formula, can calculate the location of pixels (be line number, row number) of this intersection point on image.

line＝INT{(x-x ₀)/Δx}

pixel＝INT{(y-y ₀)/Δy}

In above formula, (line, pixel) is respectively the line number and row number of intersection point respective pixel on orthography; (x ₀, y ₀) be orthography upper left corner plane projection rectangular coordinate value; Δ x and Δ y are respectively orthography in the spatial resolution size of x direction and y direction; INT is rounding operation.

According to above-mentioned steps, ask each pixel of emulating image (comprise forward sight, face and backsight) corresponding pixel coordinate on orthography, be line number and row number, be not directly to get on orthography this grey scale pixel value as the gray-scale value of simulating image, but centered by this pixel, consider this pixel some pixels around simultaneously, adopt bilinear interpolation algorithm to utilize this grey scale pixel value and the gray value information of the corresponding emulating image pixel of field grey scale pixel value interpolation calculation around thereof.Bilinear interpolation algorithm is with reference to correlation theories knowledge, and this aspect does not describe in detail.

Chang'e I detector take below as example, further describe the implementation procedure of the inventive method.

First, according to satellite nominal orbit parameter emulation Chang'e I detector orbital data.

Adopt STK (Satellite Tool Kit) software emulation Chang'e I detector orbital data here.According to above-mentioned Chang'e I detector nominal orbit parameter, in STK software emulation the orbital data of 2008-11-01T08:05:00.000 to Chang'e I detector around-the-moon flight during 2008-11-02T08:05:00.000, sampling interval is 1 second, the moon, the radius of a ball was got 1737.4 kilometers, and the simulation parameter of concrete input sees the following form:

Table 2 track is imitated straight parameter

Parameter	Parameter value
		Semi-major axis (kilometer)	1937.4km
Excentricity	0.000
		Orbit inclination (degree)	90
Right ascension of ascending node (degree)	265.24
		Perilune angular distance (degree)	248.05
Flat perilune angle (degree)	66.17

Secondly, emulation Chang'e I detector attitude data.

According to experimental formula emulation below and the attitude data in above-mentioned orbital data same time coverage, sampling interval adopts 1 second, and sampling instant is identical with orbital data, and wherein three axis stabilized satellite attitude data meets sinusoidal variations rule.

${\mathrm{\&theta;}}_{\mathrm{phi}}=a_{\mathrm{phi}}\cos \left(\frac{2\mathrm{\&pi;t}}{u_{\mathrm{phi}}}\right)+b_{\mathrm{phi}}\sin \left(\frac{2\mathrm{\&pi;t}}{T_{\mathrm{phi}}}\right)$

${\mathrm{\&theta;}}_{\mathrm{omega}}=a_{\mathrm{omega}}\cos \left(\frac{2\mathrm{\&pi;t}}{u_{\mathrm{omega}}}\right)+b_{\mathrm{phi}}\sin \left(\frac{2\mathrm{\&pi;t}}{T_{\mathrm{omega}}}\right)$

${\mathrm{\&theta;}}_{\mathrm{kappa}}=a_{\mathrm{kappa}}\cos \left(\frac{2\mathrm{\&pi;t}}{u_{\mathrm{kappa}}}\right)+b_{\mathrm{kappa}}\sin \left(\frac{2\mathrm{\&pi;t}}{T_{\mathrm{kappa}}}\right)$

θ _phifor the angle of pitch, θ _omegafor roll angle, θ _kappafor crab angle, t is sampling instant, θ _phi, θ _omega, θ _kappaexpression-form is identical, and just coefficient is different, and coefficient value sees the following form:

Table 3 Attitude Simulation parameter

Coefficient	Angle of pitch phi	Roll angle omega	Crab angle kappa
				a	0.1	0.0	0.1
T	240.0	320.0	220.0
				b	-1.0	0.5	-1.0
u	140.0	220.0	120.0

Then, prepare orthography data and Law of DEM Data.

The present invention utilizes the orthography data of identical geographical coverage and Law of DEM Data as input, and this geographic range will be passed through in substar position corresponding to almanac data that above-mentioned emulation generates.

Law of DEM Data is to be defined in X, on the discrete point of Y territory (rectangle or triangle), with elevation, express the digital document of surface irregularity form, in the present invention, be used for expressing true menology, for solve each pixel of emulating image corresponding to measurement vector the intersection point with true lunar surface, or the scientific exploration data obtained of the moon exploration task such as region Apllo15, Apollo16, Apollo17.

Orthography data are the plane pictures after aviation (or space flight) photo is carried out several topographic corrections and inlayed, in the present invention, be used for expressing menology texture information, for obtaining the gray-scale value of each pixel of emulating image, using in one embodiment of the invention and being taken at spatial resolution that U.S. Clementine moon exploration task in 1994 obtains is the image of inlaying of 100 meters.

Finally, generate simulating image.

First, utilize the camera geometric parameter providing in table 1, according to formula (1a), formula (1b) and formula (1c), build respectively forward sight, face the measurement vector with each pixel of backsight simulating image; Secondly, utilize satellite orbit data and the almanac data of emulation, above-mentioned measurement vector is transformed into a month solid coordinate system from image coordinate system; Then, according to the method in step 3 of the present invention, calculate the intersection point of this measurement vector and digital elevation model; Finally, according to position of intersecting point, adopt bilinear interpolation algorithm to obtain the grey scale pixel value of the corresponding simulating image of this measurement vector from orthography data.Repeat above-mentioned steps, the gray-scale value of each pixel of node-by-node algorithm simulating image (comprise forward sight, face and backsight image).

The image simulation method of using the present invention to propose, for the research work of the moon three line-scan digital cameras provides reliable simulation data source, for further carrying out three-line imagery matching algorithm and area adjustment Processing Algorithm provides view data.

Above-described specific embodiment; object of the present invention, technical scheme and beneficial effect are further described; institute is understood that; the foregoing is only specific embodiments of the invention; be not limited to the present invention; within the spirit and principles in the present invention all, any modification of making, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (5)

1. an emulation mode for the moon three line-scan digital camera images, the method comprising the steps of:

Step 1, emulation lunar exploration satellite orbit data, orbit parameter comprises orbit altitude, orbit inclination and excentricity;

Step 2: emulation lunar exploration attitude of satellite data;

Step 3: according to satellite orbit and attitude data, utilize the mode of projection-back projection to obtain the subpoint position of projected light beam corresponding to each pixel of three line-scan digital cameras on digital elevation model;

Step 4, according to described subpoint position acquisition grey scale pixel value, wherein

Step 3 further comprises:

Step 301, sets up camera imaging model, builds the measurement vector of each pixel;

Step 302, is transformed into a month solid coordinate by measurement vector from image coordinate;

Step 303, solves the intersection point of the moonscape that measurement vector and Law of DEM Data express, and adopts method iterative measurement vector and this surperficial intersection point of projection-back projection in this step; Step 303 further comprises: the first step, solves the intersection point A of the positive spheroid table of measurement vector and the moon; Second step, is converted to latitude and longitude coordinates and height value by a month solid three-dimensional rectangular coordinate of intersection point A, then on Law of DEM Data, inquires about the spot elevation B that this longitude and latitude is corresponding; The 3rd step, calculate the distance that B point and A are ordered | AB|; The 4th step, if distance value | AB| can not meet the demands, and the vertical line of crossing the B Dian Zuo OA of projection ray obtains intersection point point C, then on Law of DEM Data, inquires about the spot elevation D that this longitude and latitude is corresponding; The 5th step, calculate the distance that D point and C are ordered | DC|; Repeat the 4th step～five step, until the distance value in the 5th step meets the demands, iterative computation finishes, and obtains the intersecting point coordinate of projected light beam and digital elevation model;

Wherein step 301 further comprises:

Vector with represent respectively forward sight, face and the measurement vector of rear view as each pixel, wherein:

$\stackrel{\&RightArrow;}{p_f}=\left[\begin{array}{c}{x}_{P_f}\\ y_{P_f}\\ z_{P_f}\end{array}\right]=\left[\begin{array}{c}f\&times;\tan \left(\mathrm{\&alpha;}\right)-x_0\\ (c_{P_f}-c_0)\&times;\mathrm{ps}-y_0\\ -f\end{array}\right]---\left(1a\right)$

$\stackrel{\&RightArrow;}{p_n}=\left[\begin{array}{c}{x}_{P_n}\\ y_{P_n}\\ z_{P_n}\end{array}\right]=\left[\begin{array}{c}-x_0\\ (c_{P_n}-c_0)\&times;\mathrm{ps}-y_0\\ -f\end{array}\right]---\left(1b\right)$

$\stackrel{\&RightArrow;}{p_b}=\left[\begin{array}{c}{x}_{P_b}\\ y_{P_b}\\ z_{P_b}\end{array}\right]=\left[\begin{array}{c}f\&times;\tan \left(\mathrm{\&alpha;}\right)-x_0\\ (c_{P_b}-c_0)\&times;\mathrm{ps}-y_0\\ -f\end{array}\right]---\left(1c\right)$

In formula, ps is three line-scan digital camera detector pixel sizes, be respectively picture point P _f, P _n, P _bimage coordinate, the solid angle that α is camera, forward sight and face or face and backsight between angle, represent picture point P _f, P _n, P _bforward sight, face with backsight linear array on column position, (x ₀, y ₀) be the picture planimetric coordinates value of principal point, unit is pixel, c ₀be the reference point row-coordinate of camera, f is the focal length of camera.

2. method according to claim 1, is characterized in that, adopts STK software emulation Chang'e I detector orbital data.

3. method according to claim 2, is characterized in that, step 4 further comprises: according to this position of intersecting point, from existing menology view data, obtain image greyscale value, as the gray-scale value of this pixel.

4. method according to claim 3, is characterized in that, step 4 further comprises: according to position of intersecting point, adopt bilinear interpolation algorithm to obtain the grey scale pixel value of the corresponding simulating image of this measurement vector from orthography data.

5. method according to claim 4, is characterized in that, described attitude data and orbital data are in same time coverage.