1:250,000 remote sensing image map is 1:250,000 remote sensing geological interpretation and other scales of remote sensing special interpretation of the necessary basic image, which includes 1:250,000 remote sensing image maps and remote sensing orthophoto maps of two kinds. It is mainly used in routine geological surveys of geology, minerals and hydrology, as well as in the interpretation, extraction and classification of ecological and environmental factor information. The production process includes geographic data processing, full-band data radiometric correction, geometric correction, alignment, image mosaicing, data fusion and geocoding. Although the two image map production methods are more or less the same, due to the use of digital elevation model data (DEM) in the orthophoto map production process for elevation correction, so the geometric accuracy of the image is higher for mountainous areas with large differences in terrain elevation; and image maps are more suitable for plains and hilly areas with small differences in terrain elevation. For this reason, in practice, should be based on the work area of the specific terrain height difference and the degree of cutting their own choice, in order to fully meet the accuracy of the interpretation into the map for the purpose.
4.2.1 Geographic Data Processing
Includes the processing of 1:250,000, 1:100,000 topographic maps and digital elevation model (DEM), raster map (DRG) data in the form of paper media. The purpose is to provide geographic elements and control information for the production of remote sensing image maps and remote sensing orthophoto maps, and at the same time to provide working digital maps for remote sensing geological interpretation and field geological survey.
4.2.1.1 Digital Elevation Model (DEM) Production
The DEM data can be purchased directly from the National Center for Basic Geographic Information (NCBGI), or it can be acquired from topographic maps. The method of acquiring from topographic map is as follows: firstly, the 1:100000 topographic map is scanned, and the method of contour vectorization using human-computer interaction is carried out in accordance with a certain contour distance by the map rapid recording system for contour refinement, vectorization, editing, assigning values, and processing of spatial coordinate orientation; and then, according to the distribution range of interpolation points, the interpolation is divided into three categories: overall interpolation, block interpolation, and point-by-point interpolation, and the interpolation method (e.g., interpolation method) is applied. According to certain interpolation methods (such as Kriging method, etc.), the interpolation of contour lines is obtained to extract the elevation information; and then according to the corrective unit, the DEM mosaic and data format conversion are carried out to generate the mosaic DEM of the whole area; finally, the splicing accuracy is checked whether it meets the requirements, and the method is to check whether there is any error in the DEM by generating a DEM halo rendering map.
4.2.1.2 Raster Map (DRG) Production
DRG is a raster data file formed by scanning, geometric correction and color correction of 1:100000 scale topographic map, and its content, geometric accuracy and color are consistent with the original map. Production methods and steps are as follows.
(1) topographic map scanning
The paper topographic map will be scanned in accordance with a certain scanning resolution (generally 150-300dpi), stored in TIF image format.
(2)Generate control points
Using the standard map information set by the user, the intersection points of the kilometer grid will be automatically calculated as control points. Before generating the plot control points, you need to set the plot information and specify the inner plot contour points, the steps are as follows:
1) Set the plot information.
a.Sheet number. The standard sheet number of the map.
b.Grid spacing. The grid spacing of the standard map sheet, the value of which should be consistent with the grid spacing of the correction map.
c. Coordinate system. Map using the coordinate system, mainly 54 coordinate system and 80 coordinate system. If you choose geodetic coordinates, the standard map frame generated uses geodetic coordinates (unit: m), otherwise it uses map coordinates.
2)Set the control point information of the generated map frame.
a. Plot coordinates. Locate the inner map outline points by selecting the map coordinate points on the image.
b.Minimum Interval. The minimum spacing at which control points are discarded when generating control points.
3) Locate inner map contour points.
Locate the four inner map contour points on the image. Completing the parameter setting and the input of inner map contour point information, the theoretical coordinates of the control points are automatically calculated, and the image coordinates of the control points are back-calculated according to the theoretical coordinates.
(3) Sequential Modification of Control Points
The image coordinates of the control points generated from the map are the image coordinates back-calculated according to the theoretical coordinates of the intersection points of the corresponding kilometer grid, but due to the existence of a certain amount of distortion and deformation in the original image. Therefore, the value is not necessarily the same as the coordinate value of the corresponding kilometer grid intersection point on the original image, and the points need to be corrected.
(4) Grid-by-Grid Correction
It is necessary to input the image range (i.e., the logical coordinate range of the corrected image), the image output resolution, and the image outer contour (i.e., the outward expansion distance relative to the inner contour of the map, with the same unit as the map coordinates). By setting the outer contour distance, the image within a certain distance outside the boundary of the inner contour of the image frame will not be distorted in the image correction process.
(5)Raster map control accuracy requirements
Correct the control point residuals less than 1m; resampling interval 1m; map contour points, kilometer grid and its intersection coordinates shall not be more than 1m deviation.
1:100000DEM grid spacing and elevation error requirements for the DEM grid: flatland DEM grid spacing of 50m, the elevation of the error in the 6m; hill DEM grid spacing of 50m, elevation error in the 6m; DEM grid Spacing 50m, elevation error 10m; low mountain DEM grid spacing 50m, elevation error 10m; high mountain and very high mountain areas in the elevation error according to the corresponding relaxation to 1.5 times.
(6) Accuracy Evaluation
Raster map accuracy evaluation, including the quality assessment of the original map quality assessment of the map, the quality assessment of the corrected generation of DRG and the standard map frame fit check.
1) Original map quality assessment. This item is to evaluate the quality of the original data produced by the raster map, mainly reflecting whether the original map has folds and whether it is equalized when scanning. If the quality of the original map is not good, the raster map corrected will certainly be affected.
To evaluate the quality of the original map, it is first necessary to sequentially modify the control points, and when all the control points have been modified, the values in the map quality file reflect the quality of the original map image, and its file parameters are the maximum residual error and the center error before image correction. The maximum residual value reflects the point number and deviation value of the control point with the largest deviation in the original map.
2) Correction map quality assessment. This item is used to assess the quality of the corrected DRG data. After completing the grid-by-grid correction, the quality assessment file reflecting the image correction is generated by locating the four inner contour points of the image according to the information of the map frame and the method of adding inner contour points in the control point section of the map frame generation, and the parameters of the file are the median error of the corrected image, and the value of the median error reflects the overall quality of the corrected image. Diagonal dimension check (unit: m): upper edge, lower edge, left edge, right edge, diagonal 1, diagonal 2, contour edge length and diagonal dimension check, by comparing the detection value of the contour edge length of the image frame with the theoretical value, to check whether the contour edge length and the length of each edge of the diagonal line comply with the requirements of accuracy.
3) Map frame nesting check. When evaluating the quality of DRG data generated by calibration, it is also possible to check whether the accuracy of the kilometer grid is within the specified limits by comparing the theoretical grid generated with the kilometer grid on the calibration map. The quality of the corrected DRG data can be judged by checking its fit.
(7)Storage Format
The storage format of DRG produced by ENVI software is *.tif and *.img; the storage format of DRG produced by MapGIS system is *.MSI.
(8)Usage
Raster map is the basic geo-referenced image for the production of remote sensing imagery maps, the generation of digital elevation model (DEM) data, and geometric correction. basic georeferenced images.
4.2.2 Image Preprocessing
In order to maintain sufficient information and clarity of the premise of the noise and banding of the image, the need for neighboring pixels through the gray value of the substitution method, low-pass filtering method, the whole line substitution method and the Fourier Transform method of filtering to remove the noise, bands of the filtering process, the radiometric distortion of the image of the radiation of the larger corrective processing.
4.2.3 Correction and alignment
4.2.3.1 Correction and alignment model selection
More than two kinds of correction models, physical and fitting polynomial, are used. Correction and alignment should be performed for all bands.
The physical model is suitable for image data that can provide strict satellite ephemeris parameters, and requires both DEM data and control points to be distributed in the whole scene; the rational polynomial model is suitable for satellite data that is difficult to obtain the external geometric parameters of the linear sensors and whose attitudes are very complex, and requires both DEM data and control points to be distributed in the whole scene; and the geometric polynomial model is suitable for the flat area, and is usually used to Handling areas where it is difficult to provide satellite ephemeris parameters and DEM data for image acquisition. Generally, according to the data source, the physical model is prioritized for areas with large terrain elevation differences, followed by the rational polynomial model for orthorectification using DEM data, and the plain area for geometric correction of the image using 1:100000 DRG information and the geometric polynomial model.
4.2.3.2 Control point selection
Control points should be controlled around the image and evenly distributed. The number of control points should be determined according to the correction model and terrain conditions. Physical model according to the satellite ephemeris parameters to establish a rigorous model, select 9 control points can be, usually more than 20, the model requires the whole scene data have control point distribution; fit polynomial model and its corrective order term (n) related to the n = 1, the minimum requirement of no less than 7 control points per scene, usually more than 9; when n = 2, each scene to select 13 to 16 control points is appropriate. The model requires that the whole scene data are distributed with control points.
4.2.3.3 Correction and alignment control point error requirements
Flat terrain corrected control point error of 1 to 1.5 pixels, hilly terrain corrected control point error of 1 to 1.5 pixels, mountainous terrain corrected control point error of 1.5 to 2 pixels, the maximum residual error of the corrected control point is not more than 2 times the error.
Flat terrain alignment control point error of 0.5 to 1 pixel, hilly terrain alignment control point error of 0.5 to 1 pixel, mountainous terrain alignment control point error of 1 to 1.5 pixels, alignment control point maximum residual error does not exceed 2 times the error.
Resampling methods: including neighborhood method, bilinear interpolation method and cubic convolution method.
For digital orthophoto map (DOM) resampling, the resampling interval should be determined according to the scale of the map, 1:250,000 scale resampling interval of 30m; 1:100,000 scale resampling interval of 15m; DOM edge limit requirements for the flat terrain edge limit of 0.8mm, hilly terrain edge limit of 0.8mm, mountainous terrain edge limit of 1.2mm. For roads, rivers and other linear features, even if the margin limit complies with the above provisions, when the mosaic image appears heavy shadow, blurring, should be processed by the margin.DOM image should be clear, rich in texture information, and try to maintain a uniform tone and moderate contrast between the scene and the scene of the image.
4.2.4 Image Fusion
Image fusion refers to the use of a composite model structure, the remote sensing data from different sensors or with different types of data sources to provide information to obtain high-quality image information, and at the same time to eliminate the redundancy of information between the sensors to reduce the uncertainty, improve the accuracy of the decoding and reliability, in order to form relatively complete and consistent information display on the target. Information display. Fusion of panchromatic data with multispectral data, SPOT and TM data correction results, for example, ETM+ (panchromatic) and TM7, 4, 1, TM5, 4, 3, TM5, 3, 2; SPOT and TM5, 3, 2 fusion, etc., to form a fusion image that combines both high-resolution spatial information and multispectral color information. The fusion methods include principal component analysis, weighted multiplication, IHS transformation, and many other methods.
Image fusion matching accuracy check can be carried out using the image fusion method or the image stacking method, the matching accuracy is required to be 0.5 pixels for plains and hilly areas, with a maximum of no more than 1 pixel; mountainous areas can be appropriately relaxed to 1.5 pixels. Before fusion, the image must be adjusted to improve the brightness of the high-resolution data, enhance the local contrast, highlight the texture details, reduce noise; color enhancement of multi-spectral data, widen the color contrast between different types of land, highlighting its multi-spectral color information.
After fusion, check whether there are phenomena such as ghosting and blurring. Check the image texture details and colors, judge whether the processing before fusion is correct, if there are problems, return to reprocessing. If the brightness of the image after fusion is low and the gray scale range is narrow, then linear stretching, adjusting the brightness contrast and other methods can be used for processing, and in the process, the spectral and spatial information of the fused data should be preserved as much as possible.
4.2.5 Image mosaic
Standard map involves multi-scene data or multiple corrected partitions, must consider the indirect edges of the image, the edge of the limit difference between the flat and the hills are 0.8mm; mountain 1.2mm.
Digital mosaics is to choose a point of the same name as a mosaic of the control points within the overlap of neighboring images, the requirement of the two scenes of the same name of the features in the strict alignment, the fitting in the error of about 1 image element. Error in the fitting of about 1 pixel; between the two images need to match the brightness to reduce the brightness difference; mosaic splicing line selection, whether using the interactive method or automatic selection, are required to be a folded line or curve; on both sides of the splicing point need to choose the "weighted average method" for the brightness smoothing to further improve the quality of the image mosaic.
Check the edges can be used to image overlay method or check point selection method. Image superposition method of docking image superposition, combined with visual reading and point counting to extract the error; check point selection method by selecting the DOM image of the common **** area of the same name point, calculate the error of its worse in the error.
When the edging error exceeds the specification requirements, the reason should be analyzed and returned to the previous process to check and modify the control points; if the edging error meets the requirements, but some features (such as roads, rivers) are misplaced, resulting in the mosaic image of ghosting and blurring, the edging should be corrected.
The mosaic image should ensure that the color tone is uniform, the contrast is moderate, and the overlap of the edges of the overlap zone does not allow the emergence of obvious blurring or ghosting. In order to ensure that the edges are natural, the edges of the image should have an overlap of 10 to 50 pixels.
4.2.6 Graphic finishing and information management
4.2.6.1 Graphic finishing
The content of graphic finishing includes the inner graphic outline, outer graphic outline and coordinate notation, the requirements are as follows:
1) The inner graphic outline should be curved, the east-west graphic outline can be plotted as a straight line, and the north-south graphic outline is an arc, and it can be expressed as a straight line in segments. The width of the contour line is 1 image element.
2)The map contour line is parallel to the inner map contour line, and the interval between the inner map contour line is 10mm, the width of the main map contour line is 1mm, and the width of the secondary map contour line is 1 image element, and the two are parallel to each other with a distance of 2mm.
3)The content of the map contour line coordinates is the latitude, longitude and kilometer network. Outside the outline of the longitudinal difference of 15', latitude and longitude difference of 10' intervals, latitude and longitude coordinates, note 2mm long, 1 pixel wide short line between the main outline of the map and the outline of the sub-map, through the map of the kilometer network intervals of 10km.
The four corners of the outline of the latitude and longitude note marked on the four corners of the outline of the inner extension on both sides of the line, the word header facing up. Longitude notes across the meridian of the left and right, the left note "degrees", the right note "minutes" and "seconds"; latitude notes across the latitudinal line up and down, the upper note "degrees ", the next note "minutes", "seconds".
Kilometer network notation requirements for each square mile line in the map between the outline of the two digits of its coordinate value (km), the first and last square mile line and the number of hundred kilometers of the square mile line notation should be noted out the full number of (km), in the south and north of the outline of the two kilometers between the two kilometers of the square line of the right side of the line, more than one hundred digits of the square mile line of the left side of the line, the east, the west of the map between the two kilometers of the two kilometers of the top of the square mile line.
The coordinate notation is in Song font. The character height of the whole 10km is 3mm, and the character height of the number and the whole thousand kilometers is 2mm.
4.2.6.2 Figure finishing and notation
1) Figure finishing requires labeling of the title, the table of joining of the map, the numerical scale and the line scale, and the confidentiality level, and so on.
a. Figure name. With a horizontal note in the north outline of the center position, the font in bold, the height of the word is 10mm, the word spacing is 10mm; the name of the map below the note of the number of the map, the font in bold, the height of the word is 5mm.
b. Scale. Labeled in the center of the outline of the south map. The digital scale and linear scale should be plotted at the same time.
c. Legend content. Including geographic and thematic elements. Generally configured on the outside of the east map outline, arranged from top to bottom along the outer map outline, with the top leveled with the north inner map outline.
d. Map splice table configuration. On the outside west side of the north map outline.
e. Figure classification. Classified, secret, internal use of three kinds of drawings. Classified labeling in the north of the outline of the east, the last word aligned with the east of the outline of the internal map. The font is Song, and the height of the character is 5mm.
f. Notes on the west side of the outline of the south map. Including the type of remote sensing data used, time phase and band combination, control data, etc.. The font is in Song, and the height of the character is 5mm.
g. Note on the east side outside the outline of the south map. Operational units, font in Song, character height is 8mm.
2) Note geographic name, vector elements, thematic elements and other information according to the requirements of the application. The name note is in Song font, and the character height is twice as high as that of the line drawing topographic map.
4.2.6.3 Information Management
Taking the standard 1:100000 topographic map sheet as a unit, the DOM image is generated by sheet. On the basis of this, the content of map finishing is superimposed in layers to form DOM information management file, and the content and order of each layer are map outline finishing, notation, administrative boundary and DOM.
4.2.7 Inspection and Acceptance
1) The image map should strictly conform to the requirements of the technical design and the mission statement, and satisfy the needs of the application.
2)The image map should have clear image, moderate contrast, no color deviation, rich information and outstanding level.
3)The map outline size, kilometer network, latitude and longitude, inside and outside the map frame finishing and notation should meet the requirements.
4)Mathematical accuracy check: randomly select more than 25 uniformly distributed points in each map, read the coordinates of the feature points with the same name as the true value on the line topographic map, digital map, or image map at a scale of 1:100,000 or above, and calculate the medium error of the randomly sampled points.
1:250 000 Technical Guidelines for Remote Sensing Geological Interpretation
Equation: m is the center error of the points, mm; Δx, Δy is the difference of the coordinates of the random sampling points, mm; n is the number of random sampling points.
The maximum residual difference of the random sampling point does not exceed 2 times the center error as qualified.
4.2.8 Application of 1∶250000 Remote Sensing Image Map
4.2.8.1 Application of different band combinations of image maps
Remote sensing image map band combinations should be based on the application of image maps for the purpose of mapping the area of the situation of the features and the size of the image information and other factors to be selected. For TM/ETM+ and ASTER multispectral data, the required band combinations should cover all bands from visible (B1, B2, B3), near infrared (B4) to mid-infrared (B5, B7), with the smallest correlation coefficients between the bands, the richest geologic information, and the ability to have the largest amount of information, which is favorable for the interpretation of the lithology and the large tectonic information, and the commonly used wave band combinations are B5, B4, B3. In the arid and bare area, B7, B4, B1 band combination is selected; in the vegetation covered area, the image of low vegetation season in winter is preferred to minimize the influence of vegetation, and B5, B3, B2 band combination is selected, which is relatively low affected by vegetation, and has better recognizability for image interpretation, and the best effect of geologic interpretation; the image after fusion of ETM+ (full-color) with TM7, 4,1, TM5, 4,3, and TM5,3, respectively. , 2 fused images with better geologic interpretation.
CEBRS data are usually selected for B2, B3 and B4 combination.
4.2.8.2 Application of different data sources and different scale image maps
1)In order to meet the accuracy requirements of 1:250,000 scale remote sensing geologic survey, the scale of its image maps should be 1:100,000.
2)1:50,000 scale fused image is an important remote sensing 1:250,000 remote sensing geologic survey information.
3)TM/ETM+ and ASTER image maps are multi-layered, colorful, informative, and have better reflection on different geological phenomena. Therefore, TM/ETM+ and ASTER data should be the best data source for 1:250,000 remote sensing geological survey.
4)The fusion image formed by SPOT and TM is outstanding in interpreting the ancient volcanic institutions due to its high resolution and strong stereoscopic sense, but its color tone is not as rich as that of the TM image itself, and the shadow is large, so it can only play an auxiliary role in lithology delineation.
5)The fusion of Radar and TM image is not rich in color tone level, and compared with the radar image, there is no greater advantage in the stereoscopic effect and shadow pattern, and this kind of film is not the preferred image for 1:250,000 remote sensing mapping.
6)From the viewpoint of data accessibility, comprehensive application effect and the ability to solve geological problems, the remote sensing geological interpretation in 1:250000 remote sensing geological survey should be based on 1:250000 scale image maps, supplemented by 1:100000, and interactive interpretation should be carried out in order to ensure that the results of the interpretation are reproducible.
7)Indoor interpretation should make full use of the advantages of integration of remote sensing orthophoto maps and GIS system, and carry out composite processing and interpretation of multi-source data.
8)Orthorectified remote sensing image maps and three-dimensional visualized remote sensing image maps can better highlight the landscape characteristics of topography and geomorphology, and can more intuitively extract the tectonic, lithological zoning, ecological and geological factors, and carry out the division of geomorphological units, and so on, and thus the effect of geological interpretation is more prominent.