CN110375668A - Loess Surface mima type microrelief Surface Reconstruction based on point cloud data - Google Patents
Loess Surface mima type microrelief Surface Reconstruction based on point cloud data Download PDFInfo
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Abstract
The present invention relates to a kind of Loess Surface mima type microrelief Surface Reconstruction based on point cloud data.Method includes the following steps: 1) point cloud data acquires；2) point cloud data simplifies；3) mima type microrelief model creation.Precision of the present invention is high, easily operated.
Description
Technical field
The present invention relates to fields of measurement, especially a kind of Loess Surface mima type microrelief Surface Reconstruction based on point cloud data.
Background technique
The measurement of mima type microrelief is broadly divided into contact and contactless two methods, and it includes stylus method, mark that contact, which measures,
Bar method and chain method etc..Stylus method, which refers to, is placed on soil surface along slope surface for the fixed frame equipped with stylus, and is recorded with this
The distance of each stylus, every measurement once obtain an earth's surface contour line, are then spaced at equal intervals framework along slope surface and obtain a system
Column earth's surface contour line finally obtains slope ground surface altitude data in the hope of roughness of ground surface.Mark post method will be surveyed along runoff direction
Bar is placed in soil surface, with the ruler measurement low-lying place of slope surface to the vertical range of measuring staff, is averaged and earth's surface can be obtained
Roughness.The chain of given length need to only be risen and fallen with earth's surface height and be placed in soil surface by chain method, and it is long to calculate practical chain
The decreasing value of degree and horizontal length, mima type microrelief earth's surface rugosity that you can get it.Due to the shadow by extraneous factors such as artificial, measuring tools
It rings, contact type measurement destructible surface configuration causes certain error.
Non-contact measurement mainly includes satellite radar measurement, photogrammetric and three dimension laser scanning surreying.Satellite thunder
Geography monitor is had great potential by the SAR data of multipolarization, multi-angle up to remote sensing, can be interfered by solid and generate DEM.
But it is high to unmanned plane reliability requirement since to obtain data relative complex for UAV flight's laser radar, and laser radar often compared with
Valuableness uses the measurement of mima type microrelief less.The photogrammetric data acquisition equipment using certain resolution obtains different angles
The mima type microrelief image for spending different focal length generates reflection atural object appearance, position, height etc. by more complicated flow chart of data processing
The threedimensional model of attribute.Three-dimensional laser scanning technique creates mima type microrelief curved surface by obtaining the point cloud data of surface infrastructure to mould
Quasi- earth's surface mima type microrelief, for it, further measurement provides data support, and precision is high, and does not destroy surface infrastructure.
When constructing DEM based on point cloud data, there are mainly two types of methods: it is raw that one is the interpolation algorithms based on cloud
At such as common Kriging regression method.But the sampling error of irregular sampling data may be transmitted and amplify in this method, gesture
The precision of DEM and its derivative data must be influenced, and Interpolation Process takes a long time；Another kind is the machine based on morphologic filtering algorithm
LiDAR point cloud data DEM is carried to generate.The filtering processing of this method is more complex, and analog result depends entirely on the choosing of filtering algorithm
It takes, the degree of automation is lower.At the same time, domestic and foreign scholars are also carried out based on method of the triangle gridding to creation high accuracy DEM
More systematic research.Although these methods are used successfully to simulate specific landform, for only having simple three-dimensional coordinate information
Massive point cloud for, it is necessary to know that a variety of user's custom parameters and prior information, automatic processing are more difficult in advance.
Summary of the invention
The present invention be solve technical problem present in background technique, and provide a kind of precision it is high, it is easily operated based on
The Loess Surface mima type microrelief Surface Reconstruction of point cloud data.
The technical solution of the invention is as follows: a kind of Loess Surface mima type microrelief Surface Reconstruction based on point cloud data,
It is characterized in that the reconstructing method the following steps are included:
1) point cloud data acquires
1.1) it selects soil sample: selecting the soil of moisture content 8% -12% as soil sample；
1.2) soil sample mistake after natural air dryingSieve is to banket with the Contour farming in the cultivation measure of loess plateau
Soil sample is divided into the etching tank that 5 layers are filled in by mode；
1.3) measure of Contour farming agricultural tillage, using cross fall as tillage method, the wherein high 7- in ridge are laid on topsoil surface
10cm, ridge spacing are 20cm；
1.4) slope surface point cloud data is obtained using three-dimensional laser scanner scanning；
1.5) start rainfall after the completion of scanning, occur the drop of more apparent layered laminate or fish scale-like, slope surface diameter to slope surface
When stream starts generation, apparent rill occurs in slope surface, respectively as sputter stage, sheetflood stage, rill erosion stage；
1.6) after each stage of water erosion development, stopping rainfall when slope surface is without ponding, using three-dimensional laser scanner
Scanning obtains point cloud data, and is scanned to rill erosion half an hour after slope surface；
1.7) the ScanMaster software finally based on three-dimensional laser scanner collocation carries out Point-clouds Registration, noise spot
The pretreatment such as rejecting and extra point deletion, and stored in the form of text file；
2) point cloud data simplifies
2.1) topological relation is created using the fast convergence characteristic of Octree method, recurrence building principle and space division rule
And carry out neighborhood search；
2.2) it needs to determine smallest point spacing, i.e. minimum bounding box side length L firstmin, termination condition as recursive subdivision；
2.3) bounding box is then averagely divided into 8 sub- boxes, and the sub- box for including multiple clouds is continued to divide, directly
It is equal to given point away from until to most boy's box side length, cutting procedure is recorded using Octree；
2.4) finally, the Octree that breadth traversal generates, using the spatial distribution of data point and the corresponding relationship of bounding box,
The neighborhood point set of fast search arbitrary point P, establishes topological structure based on neighborhood point set, to realize point cloud simplification, LminValue
Range is 1-10mm；
3) mima type microrelief model creation
3.1) patch is constructed on the basis of triangle gridding；Along u to (slice direction) to the data on each slice, it
Be converted into the data point of cum rights and find out control point according still further to the boundary condition and inversion formula of B-spline curves, then again
These control points regard as ν to data point, then along ν to according to B-spline curves boundary condition and inversion formula carry out inverse, ask
It obtains control point and constitutes control grid；
3.2) obtain control grid after, carry out nurbs surface reconstruct, and can be obtained after B-spline basic function resampling from
Dissipate type digital complex demodulation.
Preferably, it in step 1.1), in order to ensure soil moisture content is up to 8% -12%, needs first to carry out test soil pre-
Rainfall processing, raininess are set as 30mm/h, duration 25min, until slope surface occurs producing stream.
Preferably, in step 1.2), horizontal direction line is set in etching tank, makes every layer of soil sample earth's surface for examination and level
Direction line is parallel；
Preferably, step 1.6) condition of raining is: according to the regularity of distribution of loess plateau erosive rainfall, with intra day ward
>=12mm is the aggressivity precipitation criteria for classifying, and raininess size 60mm/h and 5 °, 10 ° and 20 ° of the soil box gradient are arranged.
Preferably, in 3.1), during inverse, using multiple knot end-point condition, make the first, last vertex of characteristic polygon
Meet the interpolation condition of data point first, last endpoint, boundary condition is taken as free end condition, and knot vector is according to accumulative chord length method
It calculates.
Preferably, in 3.1), control vertex value range 16-32 is set, takes the control point for being applied to each control grid
Number range is 16-24, and practical control point number is according to curvature and length computation.
Preferably, three-dimensional laser scanner is Topcon GLS-1500 three-dimensional laser scanner.
Preferably, when scanning acquisition point cloud data using three-dimensional laser scanner, sampling interval is 1mm.
The invention has the following advantages that
1, compared with traditional measuring technique, the present invention uses three-dimensional laser scanning technique, has and obtains data precision
It is high, speed is fast, to measurement earth's surface without destroying the features such as；The feature of its active scanning makes data when acquiring not vulnerable to external rings
The influence of border and human factor；Meanwhile data collected can usually have with GPS device, distant view photograph combines on the spot
Higher compatibility, convenient for the data sharing between the post-processing and software of data, in mima type microrelief soil erosion monitoring and ground
The measurement of table rugosity, geological disaster simulation, Coastal erosion monitoring, three-dimensional building object is rebuild and the fields such as reverse-engineering surface reconstruction obtain
Extensive concern and application are arrived.
2, non-uniform rational B-spline (Non-uniform Rational B-splines, NURBS) has good connect
The features such as continuous property, fairness, affine-invariant features and local controllability, required memory space is less, simulates in earth's surface true shape
There is degree of precision and elasticity with analysis aspect, suitable for the Morphological Modeling of different characteristic object, especially complicated landforms shape
State improves a possibility that a large amount of terrain datas manage.The present invention by original dense unorganised point cloud create topology information and
Data reduction substantially increases the efficiency of surface reconstruction.Reconstructing method arithmetic speed based on nurbs surface is fast, easily passes through control
Control graphics shape need to be only arranged in the precision of vertex Control curve processed, time-consuming short high degree of automation by partial parameters.Laser
The nurbs surface reconstruct for scanning point cloud data, which obtains mima type microrelief DEM, has higher precision and time efficiency.Therefore, this method is easy
In grasp, it is worthy to be popularized.
Detailed description of the invention
Fig. 1 is that point cloud data simplifies neighborhood search schematic diagram；
Fig. 2 is erosion and growth stage nurbs surface quality reconstruction under 20 ° of slopes；
Fig. 3 is difference L under 20 ° of slopesminNurbs surface quality reconstruction；
Fig. 4 is difference L under each gradientminFour kinds of methods generate the accuracy comparison result figure of DEM；
Fig. 5 is precision test sampled point schematic diagram of the present invention；
Fig. 6 is the mobile analysis window size of 5 ° of slope differences and LminLower root-mean-square height value variation tendency；
Fig. 7 is different mobile analysis window sizes and LminThe trend chart of lower degree of skewness；
Fig. 8 is 16 × 16 window difference LminThe trend chart of lower degree of skewness；
Fig. 9 is 16 × 16 window difference LminThe trend chart of lower steepness；
Figure 10 is that different gradient lower surface collimation method calculates NURBS-DEM earth's surface rugosity and LminRelational graph；
Figure 11 is that different gradient lower surface collimation method calculates Kriging-DEM earth's surface rugosity and LminRelational graph.
Specific embodiment
Specific embodiments of the present invention are further described in detail with reference to the accompanying drawing:
Loess Surface mima type microrelief Surface Reconstruction based on point cloud data of the invention, comprising the following steps:
1) point cloud data acquires
1.1) it selects soil sample: selecting the soil of moisture content 8% -12% as soil sample；Soil used is Shaanxi Province Yangling District
The Hui Zong Se Lou on sloping upland surface layer is native (0~20cm), and the soil body is more loose, there is granular or crumb structure, and soil constituent includes sand
Gravel, powder and sticking grain, in order to ensure soil moisture content is up to 10% or so, need elder generation wherein moisture content is about 10% based on powder
Pre- rainfall processing is carried out to test soil, raininess is set as 30mm/h, duration 25min, until slope surface occurs producing stream；
1.2) soil sample mistake after natural air dryingSieve is to banket with the Contour farming in the cultivation measure of loess plateau
Soil sample is divided into 2m × 1m × 0.5m etching tank that 5 layers are filled in by mode, to guarantee to be consistent with actual conditions, every layer of appearance
Control is weighed about in 1.30g/cm3Within, and horizontal direction line is set in etching tank, make every layer of soil sample earth's surface for examination and level
Direction line is parallel, to ensure the homogeneity of slope surface landform and the continuity of soil；
1.3) Contour farming (Contour Tillage, CT) agricultural tillage measure is laid on topsoil surface, is with cross fall
Tillage method, wherein the high 7-10cm in ridge, ridge spacing are 20cm, and such tillage control measure has good soil and water conservation effect；
1.4) slope surface point cloud data is obtained using Topcon GLS-1500 three-dimensional laser scanner.Scanning speed is up to 30000
Point/second can carry out non-contact scanning to testee, obtain high-precision point cloud data on the basis of a foothold.
Therefore, the acquisition of Loess Surface earth's surface mima type microrelief altitude data is applicable in very much, sampling interval is 1mm, in scanning process
In immovable etching tank；
1.5) scanning after the completion of start rainfall, according to loess plateau erosive rainfall the regularity of distribution, with intra day ward >=
12mm is the aggressivity precipitation criteria for classifying, and raininess size 60mm/h and 5 °, 10 ° and 20 ° of the soil box gradient are arranged, and is occurred to slope surface
The drop of more apparent layered laminate or fish scale-like, when slope runoff starts to generate, apparent rill occurs in slope surface, respectively as splashing
Erosion stage, sheetflood stage, rill erosion stage；
1.6) after each stage of water erosion development, stopping rainfall when slope surface is without ponding, using three-dimensional laser scanner
Scanning obtains point cloud data, and is scanned to rill erosion half an hour after slope surface；
1.7) the ScanMaster software finally based on three-dimensional laser scanner collocation carries out Point-clouds Registration, noise spot
The pretreatment such as rejecting and extra point deletion, and stored in the form of text file；
2) point cloud data simplifies
Point cloud data precision acquired in three-dimensional laser scanner is 1mm, in each rainfall stage different gradient of Contour farming
Lower point cloud data amount is up to million, excessive to calculator memory consumption, is highly detrimental to the operation and processing of point cloud data.Cause
This, under the premise of guaranteeing fitting surface fairness and maximized real terrain geometrical characteristic, to improve arithmetic speed, saving meter
Space is calculated, original point cloud data need to be simplified.
Original discrete point cloud data only has simple three-dimensional coordinate information, and lacks clear spatial topotaxy, is unfavorable for
Adjacent region data point search.Therefore specific step is as follows for point cloud data simplification of the present invention:
2.1) topological relation is created using the fast convergence characteristic of Octree method, recurrence building principle and space division rule
And carry out neighborhood search；
2.2) it to guarantee that each sub- bounding box has and only 1 data point after simplifying, needs to determine smallest point spacing first, i.e.,
Minimum bounding box side length Lmin, termination condition as recursive subdivision；
2.3) bounding box is then averagely divided into 8 sub- boxes, and the sub- box for including multiple clouds is continued to divide, directly
It is equal to given point away from until to most boy's box side length, cutting procedure is recorded using Octree；
2.4) finally, the Octree that breadth traversal generates, using the spatial distribution of data point and the corresponding relationship of bounding box,
The neighborhood point set of fast search arbitrary point P, establishes topological structure based on neighborhood point set, to realize point cloud simplification, LminValue
Range is 1-10mm；
3) mima type microrelief model creation
The nurbs surface reconfiguration technique of Point Cloud of Laser Scanner is studied, and creates three on the basis of point cloud data simplifies
Angle grid calculates on the basis of triangle gridding and optimizes contour line, constructs patch, finally acquires control grid and carries out NURBS
Curve reestablishing.
3.1) patch is constructed on the basis of triangle gridding；Along u to (being in slice direction here) on each slice
Data are converted into them the data point of cum rights, according still further to the boundary condition and inversion formula of B-spline curves, find out control point,
Then again these control points regard as ν to data point, then along ν to according to B-spline curves boundary condition and inversion formula into
Row inverse acquires control point and constitutes control grid；During inverse, using multiple knot end-point condition, make characteristic polygon
First, last vertex meets the interpolation condition of data point first, last endpoint, and boundary condition is taken as free end condition, knot vector according to
Accumulative chord length method calculates；
3.2) obtain control grid after, carry out nurbs surface reconstruct, and can be obtained after B-spline basic function resampling from
Dissipate type digital complex demodulation.
Bicubic nurbs surface possesses preferable fairness, can satisfy the demand of Practical Project.The effect of weight coefficient
It is the relationship adjusted between the shape and control vertex of curved surface, for a k nurbs surface, calculates a control top
The weight coefficient of point is total (k+1) by control vertex itself and surrounding2A point determines.It will if weight coefficient increases
Curved surface pulls to control vertex, and curved surface is pushed away control vertex if weight coefficient reduces.Different weight coefficients is combined to song
The influence of face parametrization is also different, and one group of suitable weight coefficient combination gets higher the precision of surface fitting.It is double for one
Required control points are at least 16 for (surface fitting number is three times) nurbs surface three times.Nurbs surface from
During dynamicization, in certain threshold range, control point is more, and surface accuracy is higher, but calculation amount is also bigger.For the ease of control
The generation at control point reduces operand, and control vertex value range 16-32 is arranged, that is, is applied to the control of each control grid
Points range is 16-24, and practical control point number is according to curvature and length computation, so that grid creation is opened up between complying with point cloud well
Flutter relationship and topography curvature variation status.
The method of specific embodiments of the present invention is as follows:
1) point cloud data acquires
Soil used is that the Hui Zong Se Lou on Shaanxi Province, sloping upland surface layer, Yangling District is native (0~20cm), and the soil body is more loose, there is grain
Shape or crumb structure, soil constituent includes grit, powder and sticking grain, wherein moisture content is about 10% based on powder.Soil sample
The mistake after natural air dryingSieve, by Contour farming common in the cultivation measure of loess plateau be banket in a manner of, by soil sample divide
It is filled in 2m × 1m × 0.5m etching tank and (is consistent for guarantee with actual conditions, every layer of bulk density is about controlled in 1.30g/ for 5 layers
cm3Within), and horizontal direction line is set in etching tank, keep every layer of soil sample earth's surface for examination parallel with horizontal direction line, with true
Protect the homogeneity of slope surface landform and the continuity of soil.Artificially Contour farming (Contour is laid on topsoil surface
Tillage, CT) agricultural tillage measure, using cross fall as tillage method, wherein the high 7-10cm in ridge, ridge spacing are 20cm, Ci Zhonggeng
Make measure with good soil and water conservation effect.
According to the regularity of distribution of loess plateau erosive rainfall, is divided and marked as aggressivity precipitation using intra day ward >=12mm
Raininess size 60mm/h and 5 °, 10 ° and 20 ° of the soil box gradient are arranged in standard.Using Topcon GLS-1500 3 D laser scanning
Instrument, scanning speed can carry out non-contact scanning to testee, obtain up to 30000 points/second on the basis of a foothold
Take high-precision point cloud data.Therefore, the acquisition of Loess Surface earth's surface mima type microrelief altitude data is applicable in very much.
In order to ensure soil moisture content is up to 10% or so, need first to carry out pre- rainfall processing to test soil, raininess is set as
30mm/h, duration 25min, until slope surface occurs producing stream.Scanning obtains rainfall scarp slope face point cloud data (sampling interval
It is 1mm), immovable etching tank, starts rainfall after the completion of scanning during the scanning process, more apparent layered laminate occurs to slope surface
Or the drop of fish scale-like, slope runoff start generate, slope surface occur apparent rill when respectively as sputter stage, sheetflood rank
Section, rill erosion stage.After each stage of water erosion development, stopping rainfall when slope surface is without ponding, scanning obtains a point cloud number
According to, and rill erosion half an hour after slope surface is scanned.ScanMaster finally based on three-dimensional laser scanner collocation is soft
Part carries out the pretreatment such as Point-clouds Registration, noise points deleting and extra point deletion, and is stored in the form of text file,
Convenient for subsequent processing.
2) point cloud data simplifies
Point cloud data precision acquired in three-dimensional laser scanner is 1mm, in each rainfall stage different gradient of Contour farming
Lower point cloud data amount is up to million, excessive to calculator memory consumption, is highly detrimental to the operation and processing of point cloud data.Cause
This, under the premise of guaranteeing fitting surface fairness and maximized real terrain geometrical characteristic, in order to improve arithmetic speed, save
Space is calculated, original point cloud data need to be simplified.
Original discrete point cloud data only has simple three-dimensional coordinate information, and lacks clear spatial topotaxy, is unfavorable for
Adjacent region data point search.The present invention is created using the fast convergence characteristic, recurrence building principle and space division rule of Octree method
It builds topological relation and carries out neighborhood search, as shown in Figure 1.To guarantee that each sub- bounding box has and only 1 data point after simplifying,
It needs to determine smallest point spacing, i.e. minimum bounding box side length L firstmin, termination condition as recursive subdivision；Then by bounding box
Averagely be divided into 8 sub- boxes, and the sub- box for including multiple clouds continued to divide, until most boy's box side length be equal to it is given
Away from until, cutting procedure is recorded point using Octree；Finally, the Octree that breadth traversal generates, utilizes the space point of data point
The corresponding relationship of cloth and bounding box, the neighborhood point set of fast search arbitrary point P, establishes topological structure based on neighborhood point set,
To realize point cloud simplification.LminValue range is 1-10mm.
3) mima type microrelief model creation
The nurbs surface reconfiguration technique of Point Cloud of Laser Scanner is studied, and creates three on the basis of point cloud data simplifies
Angle grid constructs patch on the basis of triangle gridding, along u to (being in slice direction here) to the data on each slice,
They are converted into the data point of cum rights, according still further to the boundary condition and inversion formula of B-spline curves, find out control point, then
Again these control points regard as ν to data point, then along ν to according to B-spline curves boundary condition and inversion formula carry out it is anti-
It calculates, acquires control point and constitute control grid.During inverse, using multiple knot end-point condition, make the first, last of characteristic polygon
Vertex meets the interpolation condition of data point first, last endpoint, and boundary condition is taken as free end condition, and knot vector is according to accumulative string
Regular way calculates.After obtaining control grid, so that it may carry out nurbs surface reconstruct, and can be obtained after B-spline basic function resampling
Discrete type digital complex demodulation.
Bicubic nurbs surface possesses preferable fairness, can satisfy the demand of Practical Project.The effect of weight coefficient
It is the relationship adjusted between the shape and control vertex of curved surface, for a k nurbs surface, calculates a control top
The weight coefficient of point is total (k+1) by control vertex itself and surrounding2A point determines.It will if weight coefficient increases
Curved surface pulls to control vertex, and curved surface is pushed away control vertex if weight coefficient reduces.Different weight coefficients is combined to song
The influence of face parametrization is also different, and one group of suitable weight coefficient combination gets higher the precision of surface fitting.It is double for one
Required points are at least 16 for (surface fitting number is three times) nurbs surface three times.It is automated in nurbs surface
In the process, in certain threshold range, control point is more, and surface accuracy is higher, and calculation amount is bigger.For the ease of control control top
The generation of point reduces operand, and control vertex value range 16-32 is arranged.Take the control points for being applied to each control grid
Range is 16-24, and practical control point number is according to curvature and length computation, so that topology is closed between point cloud is complied in grid creation well
System and topography curvature change status.
According to erosion and growth stage original point cloud data nurbs surface result such as Fig. 2 institute under 20 ° of slopes of the above parameter simulation
Show.
Rill erosion stage L under 20 ° of slopesminTo reconstruct nurbs surface and its corresponding DEM such as Fig. 3 institute when 2,4,6,8mm
Show.
3.4 precision test
3.4.1NURBS-DEM compared with traditional interpolation method DEM precision
The variation of slope water erosion growth course is complex, for comprehensive and systematic research mima type microrelief water erosion growth course
The influence of numerical simulation and point cloud simplification to mima type microrelief DEM precision, based on NURBS method generate different gradient (5 °, 10 °,
20 °) water erosion growth course (BR, sputter SpE, sheetflood ShE, rill erosion RE, rill erosion half an hour after RE before rain30) difference LminMicro-ly
Shape DEM, and be compared with traditional interpolation algorithm Kriging, IDW, Natural Neighbor；Meanwhile randomly selecting three
The 10% of erosion and growth stage slope surface original point cloud data total amount is used as cross validation point under different gradient, is not involved in DEM creation.
Accuracy comparison result is as shown in Figure 4.
As shown in Figure 4, any erosion phase, works as LminFor value range in 1-8mm, each method simulates the equal of mima type microrelief DEM
Square error shows themselves in that NURBS < Kriging < IDW < Natural Neighbor, i.e. NURBS-DEM precision is best；When
LminWhen≤9mm, NURBS-DEM precision decreases.On the whole, the mima type microrelief DEM based on the generation of NURBS method is integrally equal
Square error is smaller, and the DEM root-mean-square error generated based on Natural Neighbor method is maximum.With the water erosion stage of development
Progress, root-mean-square error slightly increases, and variation in 30 minutes is more obvious after rill erosion stage and rill erosion, shows to invade
Degree of corrosion is deepened slightly to influence DEM precision size, and DEM precision deepens slightly to be declined with erosion.
3.4.2 earth's surface three-dimensional appearance precision evaluation
Although the evaluation of error precision can reflect the altitude data precision of DEM to a certain extent, only the finger of voucher one
Mark and can not be fully described the quality of DEM.Therefore, it in order to further evaluate the feasibility that nurbs surface generates DEM, should add
It is verified with other analysis methods.Surface topography refers to the comprehensive morphologicals such as surface roughness, percent ripple and surface shape, table
The feature of three form error, surface defect and surface roughness aspects is contained in the primary morphology of face.International Organization for standardization
(ISO) ISO25178 standard series has been formulated for the analysis of surface three dimension form error, it is specified that the survey of 3 d surface topography
The basic parameter of amount standard and assessment parameters, evaluating earth surface three-dimensional appearance precision can be divided into height parameter, spatial parameter and mixing
Parameter.Wherein, height parameter is used to describe the statistical nature of earth's surface pattern amplitude, characterizes in earth's surface three-dimensional appearance short transverse
Feature.Therefore, carrying out evaluation to DEM surface shape error using height parameter has realistic meaning.
Height parameter calculating is carried out by taking sputter stage mima type microrelief DEM under 5 ° of slopes as an example, first using in ArcToolbox
Creation fishing net in Data Management tool carries out fishing net segmentation to DEM, and each fishing net is dimensioned to 1mm × 1mm,
To ensure when carrying out mobile analysis window traversal, one and only one most attribute point in each window；On this basis, raw
At the attribute point simultaneously with original height value and simulation height value, and it is based on each phase of Coordinate generation of attribute point (x, y)
Corresponding and unique ranks number, are programmed using C# language, and each grid has original point cloud number in ensuring mobile analysis window
It on the basis of, is traversed using 3 × 3,9 × 9 and 16 × 16 windows, and calculates the height parameter that each window corresponds to attribute point
Value.In order to describe the feature of mima type microrelief regional area, on the ridge for corroding the non-erosion groove in slope surface upper, middle and lower portion and erosion groove is all
Each 1 characteristic point (see Fig. 5) of selection respectively is enclosed, its root-mean-square height value (S is calculated in limited areaq), degree of skewness (Sak) and
Steepness (Sku)。
(1) root-mean-square height analysis (when doing precision test, if need to provide specific calculation formula)
By SqWith LminBetween fluctuation situation of change known to (Fig. 6), the simulation precision of mima type microrelief DEM is to original point cloud
Simplification degree it is more sensitive, difference simplify degree under put the simulated DEM of cloud Sq fluctuations it is larger.Therefore, by LminIt is different big
Small obtained DEM local terrain properties only reflect earth's surface micromorphology, are not possible to determine best Lmin.Mobile analysis window
Mouth size and SqNegative correlation.Analysis window is bigger, SqIt is smaller, in terms of control errors and landform precision analysis applicability
It is better to show, can the mobile analysis window size of preliminary judgement optimum be 16 × 16.
(2) degree of skewness is analyzed
Degree of skewness (skewness) is a kind of assessment parameters for measuring amplitude distribution curve relative to middle line asymmetry, right
For the higher slope surface mima type microrelief of a precision, when degree of skewness is negative value, surface configuration bearing length rate is positive than its value
When range it is bigger, therefore to earth's surface erosiveness show it is stronger.The mobile analysis window size of difference and LminUnder degree of skewness result
As shown in Figure 7.Work as LminWhen identical, SakSize shows themselves in that 16 × 16 < 9 × 9 < 3 × 3；Same sampled point LminWhen different, also table
Reveal identical rule.Illustrate the erosion condition description that mobile analysis window is different degrees of to mima type microrelief DEM under 16 × 16 sizes
Ability is stronger.
To the S in the case of 16 × 16 mobile analysis windowsakWith LminRelationship is analyzed, and sees Fig. 8.On the whole, when
LminWhen=5mm, SakValue closest to original point cloud data simulation DEM calculate value, illustrate 5mm minimum bounding box side length item
Corresponding simplified data DEM precision generated is higher under part, and point cloud amount is moderate after simplifying, and topological relation is clear between point cloud data
Clear, description earth's surface shape characteristic ability is strong, also closest to actual landform.Work as LminWhen > 7mm, it is super that point cloud data simplifies rate
90%, part curved surface features easy to be lost cause to simulate earth's surface excess smoothness, form distortion.
(3) steepness is analyzed
Steepness indicates the acuity of profile amplitude distribution curvilinear motion, and being mainly used for description dimensional topography surface may deposit
Peaks or valleys defect.Work as SkuIndicate that peak and deep valley are more when > 3, i.e., the loftier syntexis of landform, hypsography change greatly；
Otherwise work as SkuThen indicate that peak and deep valley are less when < 3, landform is flat.
S in the case of 16 × 16 mobile analysis windowskuWith LminRelationship is as shown in Figure 9.Steepness is much larger than 3, illustrates earth's surface
Peak or deep valley are more, meet Contour farming slope surface hypsography and change big feature；Work as LminMutation can be generated when=5mm, said
Landform variation increases in bright 16 × 16 mobile analysis windows at this time, and topological structure definitely, describes mima type microrelief fluctuations
Ability is stronger.
3.4.3 mima type microrelief earth's surface rugosity
Surface topography refers not only to the comprehensive morphologicals such as percent ripple and the surface shape of earth's surface, is also covered by this measurement of earth's surface rugosity
The index of surface relief.For research mima type microrelief, earth's surface rugosity (soil surface roughness, SSR) is one
Main physical behavior index reflects the microrelief form that earth's surface height rises and falls, and is that one of influence ground hydrology is important
Characteristic value plays a significant role the variation monitoring research of the soil erosion.Mima type microrelief DEM has the spies such as high-precision, small range
Whether point will affect earth's surface rugosity based on the DEM for simplifying point cloud data and the generation of NURBS method under the conditions of mima type microrelief, even
The calculating of erosion amount still needs further to be verified.For guaranteeing the height accuracy of mima type microrelief DEM in vertical direction, but it is simultaneous
It is particularly important to care for this mima type microrelief pattern of earth's surface rugosity.
SSR is the ratio of surface relief unit surface area and its projected area on projected horizontal face, is surface soil
One of main hydrological characteristics play a significant role the variation monitoring research of the soil erosion.In the exposed of no vegetative coverage
On sloping upland, earth's surface rugosity changes soil texture and Infiltration ability by the influence to water storage and sputter effect, in turn
Affect runoff size.Meanwhile the space relief feature of earth's surface rugosity increases runoff resistance to a certain extent, influences rainwater production
Stream and confluence.Mima type microrelief (tillage control measure, corrodes slope section at slope aspect) and rainfall (intensity, duration, rainfall size) are characterized in
The principal element for the space scale earth's surface variation of roughness that is affected.
Since Contour farming earth's surface is presented in a manner of the ditch of spaced at regular and ridge, there is apparent space distribution rule, with
The progress of erosion and growth, earth's surface mima type microrelief spatial distribution characteristic have significant change feature.It compares and manually draws digging and artificial
Cultivator, earth's surface variation of roughness difference is more obvious under Contour farming.Therefore, the present invention chooses the Contour farming measure of 60mm/h raininess
Lower different gradient (5 °, 10 °, 20 °) sputter stage difference LminLower NURBS-DEM and Kriging-DEM as basic data source,
Earth's surface rugosity is calculated using surface collimation method.
For measuring the surface collimation method of mima type microrelief DEM earth's surface rugosity, the basic principle is that by calculating arable land actual surface
Line (chain) length with earth's surface variation of roughness decreasing value, to measure earth's surface rugosity.Its calculation formula is as follows:
Cr=(1-L2/L1)×100 (1)
In formula: CrFor earth's surface rugosity；L1And L2Horizontal length respectively after the physical length of chain and placement ground.
Earth's surface coarse computing result is as shown in Figure 10, Figure 11, (5 °, 10 °, 20 °) the sputter stage under each gradient of NURBS-DEM
The linear equation degree of fitting of earth's surface rugosity and minimum bounding box side length is respectively 0.9292,0.9322,0.9379, earth's surface rugosity
Variation range is 6.925-37.465；Sheetflood stage earth's surface rugosity and the linear equation degree of fitting of minimum bounding box side length are respectively
0.9252,0.9278,0.933, the variation range of earth's surface rugosity is 5.5211-35.469；Rill erosion stage earth's surface rugosity with
The linear equation degree of fitting of minimum bounding box side length is respectively 0.9334,0.9337,0.9435, and the variation range of earth's surface rugosity is
7.937-37.520。
(5 °, 10 °, 20 °) sputter stage earth's surface rugosity is linear with minimum bounding box side length under each gradient of Kriging-DEM
Equation model degree is respectively 0.9127,0.9272,0.9308, and the variation range of earth's surface rugosity is 6.959-37.465；Sheetflood rank
The linear equation degree of fitting of section earth's surface rugosity and minimum bounding box side length is respectively 0.9084,0.9203,0.9299, earth's surface rugosity
Variation range be 6.1841-33.860；The linear equation of rill erosion stage earth's surface rugosity and minimum bounding box side length is fitted
Degree is respectively 0.9252,0.9321,0.9425, and the variation range of earth's surface rugosity is 8.349-38.984.Illustrate in different gradient
With different erosion phases, the calculated earth's surface rugosity of two kinds of mima type microrelief DEM and minimum bounding box side length have good linear correlation
Property, and all related coefficients are all larger than 0.9.
Under gradient different condition, earth's surface rugosity has similar variation tendency, as the increase earth's surface rugosity of the gradient is protected
Metastable growth trend is held, the linear equation degree of fitting with minimum bounding box side length is also in increase tendency, is illustrated with slope
The increase of degree, mima type microrelief surface relief variation increase, and earth's surface rugosity is consequently increased.Also, no matter in which kind of gradient, which kind of is invaded
Under the erosion stage, earth's surface rugosity has closely similar variation tendency.
Under gradient the same terms, sputter to sheetflood stage earth's surface rugosity slightly reduces, this may be due in rainfall
Mima type microrelief surface is acted on by raindrop impact in journey, and significant change occurs for surface soil structure, and slope surface becomes smooth compared with before rainfall, slope
Face diameter stream starts to generate, and erosion groove occurs in local location, earth's surface relative elevation value decreases, and earth's surface rugosity is finally caused to subtract
It is small.With the progress of erosion and growth, rill erosion stage earth's surface rugosity is gradually increased.This is because the soil block of earth's surface random distribution
In there are a certain number of gaps, the earth's surface rugosity calculated while also comprising nature rugosity caused by soil block distribution.With drop
The lasting progress of rain, causes soil block to degrade or migrate, and slope surface obvious rill occurs in plurality of positions, so that be separated from each other originally
Ditch is connected with ridge, eventually leads to earth's surface rugosity and changes.
More than, specific embodiment only disclosed by the invention, but protection scope disclosed by the invention is not limited thereto,
Protection scope disclosed by the invention should be subject to the protection scope in claims.
Claims (9)
1. a kind of Loess Surface mima type microrelief Surface Reconstruction based on point cloud data, it is characterised in that: the reconstructing method includes
Following steps:
1) point cloud data acquires
1.1) it selects soil sample: selecting the soil of moisture content 8% -12% as soil sample；
1.2) soil sample mistake after natural air dryingSieve, by the Contour farming in the cultivation measure of loess plateau be banket in a manner of,
Soil sample is divided into the etching tank that 5 layers are filled in；
1.3) measure of Contour farming agricultural tillage is laid on topsoil surface, using cross fall as tillage method, the wherein high 7-10cm in ridge,
Ridge spacing is 20cm；
1.4) slope surface point cloud data is obtained using three-dimensional laser scanner scanning；
1.5) start rainfall after the completion of scanning, occur the drop of more apparent layered laminate or fish scale-like to slope surface, slope runoff is opened
When beginning generates, apparent rill occurs in slope surface, respectively as sputter stage, sheetflood stage, rill erosion stage；
1.6) it is scanned when slope surface is without ponding using three-dimensional laser scanner after each stage of water erosion development, stopping rainfall
Point cloud data is obtained, and rill erosion half an hour after slope surface is scanned；
1.7) the ScanMaster software finally based on three-dimensional laser scanner collocation carries out Point-clouds Registration, noise points deleting
It pre-processes with extra point deletion etc., and is stored in the form of text file；
2) point cloud data simplifies
2.1) it is gone forward side by side using the fast convergence characteristic of Octree method, recurrence building principle and space division rule creation topological relation
Row neighborhood search；
2.2) it needs to determine smallest point spacing, i.e. minimum bounding box side length L firstmin, termination condition as recursive subdivision；
2.3) bounding box is then averagely divided into 8 sub- boxes, and the sub- box for including multiple clouds is continued to divide, until most
Boy's box side length is equal to given point away from until, and cutting procedure is recorded using Octree；
2.4) finally, breadth traversal generate Octree, using the spatial distribution of data point and the corresponding relationship of bounding box, quickly
The neighborhood point set for searching for arbitrary point P, establishes topological structure based on neighborhood point set, to realize point cloud simplification, LminValue range
For 1-10mm；
3) mima type microrelief model creation
3.1) patch is constructed on the basis of triangle gridding；The data on each slice change them to (slice direction) along u
It is counted as the data point of cum rights, according still further to the boundary condition and inversion formula of B-spline curves, control point is found out, then again these
Control point regard as ν to data point, then along ν to according to B-spline curves boundary condition and inversion formula carry out inverse, acquire control
System point constitutes control grid；
3.2) after obtaining control grid, nurbs surface reconstruct is carried out, and discrete type can be obtained after B-spline basic function resampling
Digital complex demodulation.
2. the Loess Surface mima type microrelief Surface Reconstruction according to claim 1 based on point cloud data, it is characterised in that:
In the step 1.1), in order to ensure soil moisture content is up to 8% -12%, need first to carry out pre- rainfall processing, rain to test soil
It is set as 30mm/h, duration 25min by force, until slope surface occurs producing stream.
3. the Loess Surface mima type microrelief Surface Reconstruction according to claim 2 based on point cloud data, it is characterised in that:
In the step 1.2), etching tank specification is 2m × 1m × 0.5m, and every layer of soil sample bulk density control is in 1.30g/cm3Within.
4. the Loess Surface mima type microrelief Surface Reconstruction according to claim 3 based on point cloud data, it is characterised in that:
In the step 1.2), horizontal direction line is set in etching tank, keeps every layer of soil sample earth's surface for examination parallel with horizontal direction line.
5. the Loess Surface mima type microrelief Surface Reconstruction according to claim 4 based on point cloud data, it is characterised in that:
Step 1.6) the condition of raining is: being to invade with intra day ward >=12mm according to the regularity of distribution of loess plateau erosive rainfall
Raininess size 60mm/h and 5 °, 10 ° and 20 ° of the soil box gradient are arranged in the corrosion precipitation criteria for classifying.
6. the Loess Surface mima type microrelief Surface Reconstruction according to claim 5 based on point cloud data, it is characterised in that:
It is described 3.1) in, during inverse, using multiple knot end-point condition, the first, last vertex of characteristic polygon is made to meet data point
The interpolation condition of first, last endpoint, boundary condition are taken as free end condition, and knot vector is calculated according to accumulative chord length method.
7. the Loess Surface mima type microrelief Surface Reconstruction according to claim 6 based on point cloud data, it is characterised in that:
It is described 3.1) in, be arranged control vertex value range 16-32, take be applied to it is each control grid control points range be 16-
24, practical control point number is according to curvature and length computation.
8. according to claim 1 to the Loess Surface mima type microrelief surface reconstruction described in 7 any claims based on point cloud data
Method, it is characterised in that: the three-dimensional laser scanner is Topcon GLS-1500 three-dimensional laser scanner.
9. the Loess Surface mima type microrelief surface reconstruction side according to claim 8 any claim based on point cloud data
Method, it is characterised in that: when obtaining point cloud data using three-dimensional laser scanner scanning, sampling interval is 1mm.
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