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| Quick links | Description :: Parameters :: Parameter descriptions :: Details :: References :: Related |
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InputLeft: Input left-epipolar image layer
The layer that contains the left-epipolar image to process.
InputMMLeft: Input left math model
The math-model segment for the left-epipolar image layers.
LeftEpipolarHeader: Input left-epipolar header
The header for the left-epipolar image layers.
InputRight: Input right-epipolar image layer
The layer that contains the right-epipolar image to process.
InputMMRight: Input right math model
The math-model segment for the right-epipolar image layers.
RightEpipolarHeader: Input right-epipolar header
The header for the right-epipolar image layers.
OutputEpiDEM: Output epipolar DEM layer
The name of the file that contains the output epipolar DEM layer.
OutputEpiScor: Output epipolar score
The name of the file that contains the output epipolar-correlation score.
OutputEpiRaster: Output copied epipolar-image layer
The name of the file that contains the output copied epipolar image.
OutputMMLeft: Output left math model
The name of the file that contains the output math-model segment for the left-epipolar image layers.
OutputMMRight: Output right math model
The name of the file that contains the output math-model segment for the right-epipolar image layers.
EpipolarHeader: Output epipolar header
The header for the output epipolar image layers.
OutputGeoScore: Output geocoded score
The name of the file that contains the output geocoded-correlation score.
MergeEpipImg: Merged geocoded imagery
The name of the file that contains the output mosaicked imagery used by AUTODEM.Input window
The raster window, in pixel and line coordinates, that is read from the input epipolar images. If no value is specified for this parameter, the entire layer is used by default.
Xoffset, Yoffset define the upper-left starting pixel coordinates of the window. X-size is the number of pixels that define the window width. Y-size is the number of lines that define the window height.
When you specify a value for the Upper Left Coordinate (UPLEFT) and Lower Right Coordinate (LORIGHT) parameters, this parameter is ignored.
Minimum, maximum elevation
The minimum and maximum elevation bounds within the area of interest (AOI). The units are either meters or feet, depending on the projection of the model. If no value is specified for this parameter, AUTODEM extracts the DEM range from the global elevation model.
Elevation failure value
The value given to pixels for which the generation of elevation values failed. This value should be outside the range of valid elevation values. The failure value identifies the areas that can be interpolated and filled.
Background elevation value
The background-elevation (NoData) value of the input and output DEM.
When the empty DEM file is first created, the function fills the entire DEM channel with the specified background-elevation value. In the final DEM file, this value indicates areas that have no stereo images from which to extract elevation values.
Select a value that is different from that specified for the Elevation Failure Value (FAILVALU) parameter and that is not a valid extracted elevation value for the area. For example, avoid setting this parameter to 0 in, for example, a coastal area, because a valid extracted elevation can match this value.
If this parameter is not specified, the function uses the default value of -32768.
DEM detail
The level of detail of the generated DEM. A higher level of detail requires more computation time.
Terrain type
The types of terrain in the scenes.
Data type
The type of data of the output image channel.
Pixel sampling interval
The number of image pixels between the image locations at which to compute an elevation value in both the along-row and along-column dimensions. The DEM-cell dimension will be approximately the ground-projected pixel dimension of the image data times this value.
Although a greater value for this parameter will cause the DEM to have a larger cell dimension and a lower level of detail, this computes the DEM more quickly.
Fill holes
Whether to automatically edit the DEM.
Smoothing filter
The type of filter to use when automatically editing the DEM. This parameter is available only when the Fill Holes option is selected.
Wallis filter
The Wallis filter can be useful with desert data or areas with significant shadows, such as mountainous areas or urban scenes.
OutputGeocodedDEM: Output geocoded DEM
The name of the file to which to write the output geocoded DEM. This is an optional parameter to directly create a geocoded DEM of all generated epipolar DEMs.
If a value is specified for this parameter, a composite geocoded DEM is generated from the epipolar DEMs computed individually. The geocoded DEM is written to the specified PCIDSK file.
If no value is specified for this parameter, the epipolar DEMs are generated, but no geocoded DEM is written as output. To geocode the epipolar DEMs after running AUTODEM, run the GEOCODEDEM algorithm.
This parameter is optional.
Epipolar DEM clipping
The amount of data to clip from the epipolar DEMs before merging and geocoding.
The value you specify for this parameter is the amount of the actual image data to clip. You can specify the value as either the number of pixels or as a percentage of the image size, corresponding to the value selected in the Epiolar DEM clipping units list.
For example, specifying a value of 5,10 clips five pixels from the left and right edges and 10 pixels from the top and bottom edges of the epipolar DEM.
When you specify a single value, clipping applies to all edges of the image. For example, specifying a value of 5 clips five pixels from all four edges of the epipolar DEM.
To clip based on a percentage of the image size, type a percent sign (%) after the value. For example, a value of 5%,7% clips five percent from the left and right edges and seven percent from the top and bottom edges of the epipolar DEM.
The default is blank, which means no clipping occurs. The maximum percentage value you can apply is 49 percent.
To apply this option, a value must be specified for the OutputGeocodedDEM parameter.
Epipolar DEM clipping units
The units that correspond to the value specified for the Epipolar DEM clipping parameter.
Map projection
The projection string for the output DEM. If no value is specified, the map units are determined automatically.
If METER or FEET is specified, the math model and DEM must be METER or FEET.
If a regular, Earth-referenced projection is specified, the math model and DEM must also use a regular projection (not necessarily the same one); METER and FEET are not allowed.
LCC D350 | 0 0 3.0 46.5 44.0 49.0 700000 6600000 0 0 0 0 0 0 0 0 0 -1
This parameter can specify the UTM-zone number and row, and Earth model, as follows:
UTM [mm] [r] [Ennn]
where:
The Earth model can be specified for LONG/LAT (and other units except METER or FEET), as follows:
LONG/LAT [Ennn]
This parameter can specify the SPCS-zone number and Earth model as follows:
SPCS [mmmm] [Ennn]
where [mmmm] is the four-digit zone number.
If the Earth model is not specified, it is assumed to be E000 (Clarke 1866).
Upper left coordinate
The upper-left ground x and y coordinates, in map units, for the output epipolar or geocoded DEMs.
If no value is specified for this parameter, AUTODEM calculates and uses the upper-left corner coordinate from the input images.
This parameter is optional.
Lower right coordinate
The lower-right ground x and y coordinate, in map units, for the output epipolar or geocoded DEMs.
If no value is specified for this parameter, AUTODEM calculates and uses the lower-right corner coordinate from the input images.
This parameter is optional.
Output pixel ground size (X,Y)
The resolution, in meters or feet, of the generated pixels. If no value is specified for this parameter and the Map projection (MAPUNITS) parameter, the resolution is determined automatically from the input files.
This parameter is optional.
Merge geocoded DEM option
The DEM-merging option to use when multiple epipolar DEMs are geocoded and added to the output DEM file.
When a new geocoded DEM is added to the file and it overlaps an existing geocoded DEM, you must specify the method by which to determine the pixel value to use.
SCORE (Highest score): Uses the highest score to replace the pixel values in the overlapped area by the pixel value with the highest correlation score between the existing geocoded DEM and the one that is added to the file.
Use this option only when you create the score channel during creation of the epipolar DEM.
BLEND (Blending): Uses the mosaicking method to mosaic the DEMs together with blending between DEMs. This is the default value.
This parameter is optional.
OutputVec: Output vector cutlines
A vector segment containing whole polygons that are roughly representative of the original raw-image locations.
Report
Specifies where to direct the generated report.
Available options are:
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AUTODEM generates a digital elevation model (DEM) from epipolar image pairs generated from optical or SAR sensors. The input digital images can be accompanied by any type of geometric model other than polynomial or thin-plate spline.
Matching points in a left and right input image are found using image correlation. The image disparity for the point pair is computed and this value, combined with the geometric model for each image, is used to compute the scene elevation for the corresponding scene point.
The image correlation is performed on an image pyramid that is constructed for each of the input images. The base level of an image pyramid is the original image, the next highest level is the original image resampled to a coarser spatial resolution, the level after that is the previous level resampled to a coarser spatial resolution, and so on. The location in one image that matches the current point in the other is first found at the coarsest resolution level for both images. This location is then used as the starting point for finding the match at the second coarsest resolution, and so on until the match is found in the original images.
This multi-resolution approach to image matching is faster than searching for matches in only the full-resolution images, and results in fewer false matches.
The search radius at the initial (coarsest) resolution is determined from the elevation range within the scene, provided by the Minimum, maximum elevation (MINMAXEL) parameter or extracted automatically. If the range is too narrow, some of the matches may not be found, resulting in failed values. If the range is too wide, some invalid matches may be accepted, lowering the quality of the DEM. Moreover, with SAR images, some pixels at the image-overlap-area margins may not be matched; therefore, the specified minimum and maximum elevations should be close to the expected elevation range within the scene. Notice that the automatically extracted elevation range can be too wide, particularly in scenes close to areas with large changes in elevations.
SAR DEMs
AUTODEM extracts SAR DEMs by using separate code, based on the paper cited under References.
The image matcher uses the normalized cross-correlation between a pair of epipolar SAR mages. Both images of the pair should be acquired from the same side; that is, either two descending orbit images or two ascending orbit images, preferably at the same resolution. The optimum separations with SAR images depend on the terrain type; flat or gently rolling terrain requires the largest available separations, while mountain scenes should be processed with smaller separations (but not less than 5 degrees). Scenes where separation is too small may match well, but the elevations will be highly inaccurate. Scenes with very large separation may show a large number of failed matches due to image dissimilarity.
The images are processed in horizontal strips, derived, and written sequentially to the epipolar DEM file. The height of the strips (number of lines) depends on the available memory, the selected processing window, and the level of detail specified for the DEM detail (DEMDET) parameter. The successive strips overlap, and the elevations are linearly ramped at strip margins.
The pyramiding scheme (applied within each strip) is different than that used for optical DEMs, and uses up to eight resolution levels. The raw matches are analyzed locally and smoothed according to the properties of the correlation surface in their neighborhood. The smallest holes are always filled, but the larger ones are processed according to the level of detail specified for the DEM detail (DEMDET) parameter.
With SAR data, it is not recommended that you derive full-resolution DEMs, due to a higher level of noise in such DEMs. AUTODEM uses large matching windows, which result in a certain degree of terrain surface-smoothing. In most cases, this smoothing effect will not be eliminated by extracting elevations at every pixel; therefore, an extraction interval of 2 and a DEM-detail setting of MEDIUM or LOW are recommended.
With high-resolution images, the extracted DEM may contain unwanted noise and have interior holes filled with background (as opposed to failed) values. In such cases, it is recommended that you regenerate the DEM with a higher extraction interval, a lower DEM-detail level, and a higher degree of DEM editing. If these measures still do not produce the desired result, try regenerating the epipolar pairs at a higher sampling interval than the value used initially. This will lower the resolution of the final DEM and, in most cases, improve its appearance.
The elevation datum is determined automatically based on the input data. The output elevation datum is determined by the math model. The following table shows the relationship between the output datum and the type of math model. The only math model that can have mean sea level (MSL) or ellipsoid (ELL) as output is the airphoto math model, with which the datum is controlled by the input exterior orientation.
| Math model | |||||
|---|---|---|---|---|---|
| Output datum | RPC | Toutin | Airphoto | SAR | |
| MSL | ✔ | ✔ | ✔ | ||
| ELL | ✔ | ✔ | ✔ |
After AUTODEM finishes processing you can, if necessary, convert elevation values between MSL and ELL by running the DEMZREF algorithm. For more information, follow the link to DEMZREF under Related functions.
AUTODEM generates a report depicting the elevation sensitivity to parallax, allocated memory, and the individual strip elevations and dimensions. The parallax sensitivity corresponds roughly to the RMS error of elevations extracted from well-matching pixels, although larger localized errors are common.
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Frankot, R. F., S. Hensley and S. Shafer, 1994. "Noise resistant estimation techniques for SAR image registration and stereo matching". IGARSS, California Institute of Technology, Pasadena, CA, 3 pp.
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