17. The stereo.default file

The stereo.default file contains configuration parameters that the parallel_stereo (Section 16.47) and stereo programs use to process images. The stereo.default file is loaded from the current working directory, unless a different file is specified with the -s option. The file extension is not important.

As mentioned in Section 6.1.5, all the parallel_stereo parameters can also be specified on the command line, by prepending them with two dashes. The command-line options take precedence over what is specified in this file.

A sample stereo.default.example file is included in the top-level directory of the Stereo Pipeline software distribution. That configuration is optimized for speed. See Section 6 for various speed-vs-accuracy tradeoffs of stereo algorithms.

Listed below are the parameters used by parallel_stereo, grouped by processing stage.

17.1. Preprocessing

17.1.1. Interest point determination

ip-per-tile <integer (default: unspecified)>

How many interest points to detect in each \(1024^2\) image tile (default: automatic determination). This is before matching. Not all interest points will have a match. See also --matches-per-tile.

ip-per-image <integer (default: unspecified)>

How many interest points to detect in each image (default: automatic determination, usually 5000). It is overridden by --ip-per-tile if provided.

ip-detect-method <integer (default: 0)>

What type of interest point detection algorithm to use for image alignment. 0 = Custom OBAloG ([Jak10]) implementation (default), 1 = SIFT implementation from OpenCV, 2 = ORB implementation from OpenCV. If the default method does not perform well, try out one of the other two methods.

epipolar-threshold <double (default: unspecified)>

Maximum distance in pixels from the epipolar line to search for matches for each interest point. Due to the way ASP finds matches, reducing this value can actually increase the number of interest points detected. If image alignment seems to be working well but you are not getting enough interest points to get a good search range estimate, try setting this value to a small number, perhaps in the low double digits.

ip-inlier-factor <double (default: 1.0/15)>

A higher factor will result in more interest points, but perhaps also more outliers. It is important to note that this parameter overlaps somewhat in scope and effect with --epipolar-threshold and sometimes not both are active. It is suggested to experiment with both, as well as with --ip-uniqueness-threshold below, which has a different justification but also somewhat similar effects.

ip-uniqueness-threshold <double (default: 0.8)>

A higher threshold will result in more interest points, but perhaps less unique ones.

ip-triangulation-max-error <double (default: unspecified)>

When matching IP, filter out any pairs with a triangulation error higher than this.

ip-num-ransac-iterations <int (default: 100)>

How many RANSAC iterations to do in interest point matching.

ip-nodata-radius <integer (default: 4)>

Remove IP near nodata with this radius, in pixels.

force-reuse-match-files

Force reusing the match files even if older than the images or cameras.

match-files-prefix <string (default: unspecified)>

Use the match file from this prefix. Normally contains match files created with bundle_adjust or parallel_stereo. Works only with non-mapprojected images.

clean-match-files-prefix <string (default: unspecified)>

Use as input match file the *-clean.match file from this prefix (this had the outliers filtered out). See also match-files-prefix.

matches-per-tile <int (default: unspecified)>

How many interest point matches to compute in each image tile (of size normally \(1024^2\) pixels). Use a value of --ip-per-tile a few times larger than this. See also --matches-per-tile-params.

matches-per-tile-params <int int (default: 1024 1280)>

To be used with --matches-per-tile. The first value is the image tile size for both images. A larger second value allows each right tile to further expand to this size, resulting in the tiles overlapping. This may be needed if the homography alignment between these images is not great, as this transform is used to pair up left and right image tiles.

17.1.2. Image alignment

alignment-method (= affineepipolar, local_epipolar, homography, epipolar, none)

(default = affineepipolar)

When alignment-method is set to local_epipolar, the images are divided into small tiles of size --corr-tile-size expanded by a padding of --sgm-collar-size on all sides, epipolar alignment is applied to each pair of tiles, making the stereo disparity horizontal, then a desired 1D correlation algorithm (specified via --stereo-algorithm) finds this disparity [DFMLM+14]. Then the local alignment is undone for each disparity, the resulting disparities are merged and blended across the tiles, ASP’s subpixel refinement is applied, if set via --subpixel-mode, the combined disparity is filtered, and triangulation is performed. This mode works only with parallel_stereo.

When alignment-method is set to affineepipolar, parallel_stereo will attempt to pre-align the images by detecting tie-points using feature matching, and using those to transform the images such that pairs of conjugate epipolar lines become collinear and parallel to one of the image axes. The effect of this is equivalent to rotating the original cameras which took the pictures.

When alignment-method is set to homography, parallel_stereo will attempt to pre-align the images by automatically detecting tie-points between images using a feature matching. Tie points are stored in a *.match file that is used to compute a linear homography transformation of the right image so that it closely matches the left image. Note: the user may exercise more control over this process by using the ipfind and ipmatch tools.

When alignment-method is set to epipolar, parallel_stereo will apply a 3D transform to both images so that their epipolar lines will be horizontal. This speeds of stereo correlation as it greatly reduces the area required for searching.

Epipolar alignment is only available when calculating the stereo matches using the ``pinhole`` or ``nadirpinhole`` stereo sessions (i.e. when using ``stereo -t pinhole``), and cannot be used when processing other camera types.

global-alignment-threshold (float) (default = 10)

Maximum distance from inlier interest point matches to the epipolar line when calculating the global affine epipolar alignment.

local-alignment-threshold (float) (default = 2)

Maximum distance from inlier interest point matches to the epipolar line when calculating the local affine epipolar alignment.

alignment-num-ransac-iterations (integer) (default = 1000)

How many RANSAC iterations to use for global or local epipolar alignment.

outlier-removal-params (double, double) (default = 95.0, 3.0)

Outlier removal params (percentage and factor) to be used in filtering interest points and the disparity with the box-and-whisker algorithm. Set the percentage to 100 to turn this off. These values are rather relaxed by default to not remove good data with a big spread.

disparity-range-expansion-percent (integer) (default = 20)

Expand the disparity range estimated from interest points by this percentage before computing the stereo correlation with local epipolar alignment.

17.1.3. Other pre-processing options

force-use-entire-range (default = false)

By default, the Stereo Pipeline will normalize ISIS images so that their maximum and minimum channel values are \(\pm\)2 standard deviations from a mean value of 1.0. Use this option if you want to disable normalization and force the raw values to pass directly to the stereo correlations algorithms.

For example, if the ISIS histeq tool has already been used to normalize the images, then use this option to disable normalization as a (redundant) pre-processing step.

individually-normalize (default = false)

By default, the maximum and minimum valid pixel value is determined by looking at both images. Normalized with the same “global” min and max guarantees that the two images will retain their brightness and contrast relative to each other.

This option forces each image to be normalized to its own maximum and minimum valid pixel value. This is useful in the event that images have different and non-overlapping dynamic ranges. You can sometimes tell when this option is needed: after a failed stereo attempt one of the rectified images (*-L.tif and *-R.tif) may be either mostly white or black. Activating this option may correct this problem.

Note: Photometric calibration and image normalization are steps that can and should be carried out beforehand using ISIS’s own utilities. This provides the best possible input to the stereo pipeline and yields the best stereo matching results.

skip-image-normalization

Skip the step of normalizing the values of input images and removing nodata-pixels. Create instead symbolic links to original images. This is a speedup option for mapprojected input images.

nodata-value (default = none)

Pixels with values less than or equal to this number are treated as no-data. This overrides the nodata values from input images.

stddev-mask-kernel (integer) (default = -1)

Size of kernel to be used in standard deviation filtering of input images. Must be > 1 and odd to be enabled. To be used with --stddev-mask-thresh.

stddev-mask-thresh (double) (default = 0.5)

Mask out pixels from input images where the local standard deviation score is less than this value. If set < 0, debug files (*stddev_filter_output.tif) will be written containing the filter output instead of masking out pixels.To be used with --stddev-mask-kernel.

datum (default = WGS_1984)

Set the datum. Used chiefly with RPC cameras. Options: WGS_1984, D_MOON (1,737,400 meters), D_MARS (3,396,190 meters), MOLA (3,396,000 meters), NAD83, WGS72, and NAD27. Also accepted: Earth (=WGS_1984), Mars (=D_MARS), Moon (=D_MOON).

no-datum

Do not assume a reliable datum exists, such as for irregularly shaped bodies.

skip-rough-homography

Skip the step of performing datum-based rough homography if it fails.

enable-correct-velocity-aberration

Enable velocity aberration correction for Optical Bar and non-ISIS linescan cameras (Section 11.4.2). This option impairs the convergence of bundle adjustment. It is suggested to use it though with Digital Globe images to improve the positioning, if not using bundle adjustment, whose convergence is impaired by this option.

enable-correct-atmospheric-refraction

Enable atmospheric refraction correction for Optical Bar and non-ISIS linescan cameras. This option impairs the convergence of bundle adjustment. It is suggested to use it though with Digital Globe images to improve the positioning, if not using bundle adjustment, whose convergence is impaired by this option.

left-image-crop-win xoff yoff xsize ysize

Do stereo in a sub-region of the left image [default: use the entire image].

right-image-crop-win xoff yoff xsize ysize

When combined with left-image-crop-win, do stereo in given subregions of left and right images. The crop windows can be determined using stereo_gui. It is important to note that when both of these are specified, we explicitly crop the input images to these regions, which does not happen when left-image-crop-win alone is specified. In that case we use the full images but only restrict the computation to the specified region.

left-image-clip: (string) (default = “”)

If --left-image-crop-win is used, replaced the left image cropped to that window with this clip.

right-image-clip: (string) (default = “”)

If --right-image-crop-win is used, replaced the right image cropped to that window with this clip.

threads (integer) (default = 0)

Select the number of threads to use for each process. If 0, use the value in ~/.vwrc.

cache-size-mb (integer) (default = 1024)

Set the system cache size, in MB, for each process.

dg-use-csm

Use the CSM model with DigitalGlobe linescan cameras (-t dg). No corrections are done for velocity aberration or atmospheric refraction.

aster-use-csm

Use the CSM model with ASTER cameras (-t aster).

17.2. Correlation

stereo-algorithm (string) (default = “asp_bm”)

Use this option to switch between the different stereo correlation algorithms supported by ASP. Options: asp_bm, asp_sgm, asp_mgm, asp_final_mgm, mgm (original author implementation), opencv_sgbm, libelas, msmw, msmw2, and opencv_bm. See Section 6.1.2.2 for their description.

prefilter-mode (= 0,1,2) (default = 2)

Filter used to prepare images before performing correlation. Used only with the asp_bm algorithm. Options:

0 - None

1 - Subtracted mean

Takes a preferably large Gaussian kernel and subtracts its value from the input image. This effectively reduces low frequency content in the image. The result is correlation that is immune to translations in image intensity.

2 - LoG filter

Takes the Laplacian of Gaussian of the image. This provides some immunity to differences in lighting conditions between a pair of images by isolating and matching on blob features in the image.

For all of the modes above, the size of the filter kernel is determined by the prefilter-kernel-width parameter below.

The choice of pre-processing filter must be made with thought to the cost function being used (see cost-mode, below). LoG filter preprocessing provides good immunity to variations in lighting conditions and is usually the recommended choice.

prefilter-kernel-width (float) (default = 1.5)

The diameter of the Gaussian convolution kernel used for the prefilter modes 1 and 2 above. A value of 1.5 works well for LoG and 25 - 30 works well for subtracted mean.

corr-seed-mode (=0,1,2,3)

(default = 1) This integer parameter selects a strategy for how to solve for the low-resolution integer correlation disparity, which is used to seed the full-resolution disparity later on.

0 - None

Don’t calculate a low-resolution variant of the disparity image. The search range provided by corr-search is used directly in computing the full-resolution disparity.

1 - Low-resolution disparity from stereo

Calculate a low-resolution version of the disparity from the integer correlation of subsampled left and right images. The low-resolution disparity will be used to narrow down the search range for the full-resolution disparity.

This is a useful option despite the fact that our integer correlation implementation does indeed use a pyramid approach. Our implementation cannot search infinitely into lower resolutions due to its independent and tiled nature. This low-resolution disparity seed is a good hybrid approach.

2 - Low-resolution disparity from an input DEM

Use a lower-resolution DEM together with an estimated value for its error to compute the low-resolution disparity, which will then be used to find the full-resolution disparity as above. These quantities can be specified via the options disparity-estimation-dem and disparity-estimation-dem-error respectively. This option is not compatible with map projected input images.

3 - Disparity from full-resolution images at a sparse number of points.

This is an advanced option for terrain having snow and no large-scale features. It is described in Section 5.6.

For large images, bigger than MOC-NA, using the low-resolution disparity seed is a definitive plus. Smaller images such as Cassini ISS or MER images should just shut this option off to save storage space.

corr-sub-seed-percent (float) (default=0.25)

When using corr-seed-mode 1, the solved-for or user-provided search range is grown by this factor for the purpose of computing the low-resolution disparity.

min-num-ip (integer) (default = 20)

Automatic search range estimation will quit if at least this many interest points are not detected.

cost-mode (= 0,1,2,3,4)

(default = 2 for ASP_BM and 4 for ASP_SGM and ASP_MGM) This defines the cost function used during integer correlation. Squared difference is the fastest cost function. However it comes at the price of not being resilient against noise. Absolute difference is the next fastest and is a better choice. Normalized cross correlation is the slowest but is designed to be more robust against image intensity changes and slight lighting differences. Normalized cross correlation is about 2x slower than absolute difference and about 3x slower than squared difference. The census transform [ZW94] and ternary census transform [HCW+16] can only be used with the ASP_SGM and ASP_MGM correlators. See Section 18.2 for details.

0 - absolute difference
1 - squared difference
2 - normalized cross correlation
3 - census transform
4 - ternary census transform
corr-kernel (integer integer) (default = 21 21)

These option determine the size (in pixels) of the correlation kernel used in the initialization step. A different size can be set in the horizontal and vertical directions, but square correlation kernels are almost always used in practice. (The kernel size is at most 9 x 9 with --stereo-algorithm asp_mgm or asp_sgm, and --cost-mode 3 and 4.)

corr-search (integer integer integer integer)

These parameters determine the size of the initial correlation search range. The ideal search range depends on a variety of factors ranging from how the images were pre-aligned to the resolution and range of disparities seen in a given image pair. This search range is successively refined during initialization, so it is often acceptable to set a large search range that is guaranteed to contain all of the disparities in a given image. However, setting tighter bounds on the search can sometimes reduce the number of erroneous matches, so it can be advantageous to tune the search range for a particular data set.

If this option is not provided, parallel_stereo will make an attempt to guess its search range using interest points.

These four integers define the minimum horizontal and vertical disparity and then the maximum horizontal and vertical disparity.

max-disp-spread (double) (default = -1.0)

If positive, limit the spread of the disparity to this value (horizontally and vertically, centered at the median value). Do not specify together with corr-search-limit. Use this with care. With non-mapprojected images, the valid spread of the disparity can be a few thousand pixels, if the terrain is very steep. With mapprojected images this likely should be under 100-200 pixels.

corr-search-limit (integer integer integer integer)

Set these parameters to constrain the search range that parallel_stereo automatically computes when corr-search is not set. This setting is useful when you have a good idea of the alignment quality in the vertical direction but not in the horizontal direction. For example, when using pinhole frame cameras with epipolar alignment the actual vertical search range may be much smaller than the automatically computed search range. See also --max-disp-spread.

The interpretation of these four integers is as for corr-search.

ip-filter-using-dem (string) (default = “”)

Filter as outliers interest point matches whose triangulated height differs by more than given value from the height at the same location for the given DEM. All heights are in meters. Specify as: ‘<dem file> <height diff>. Example: ‘dem.tif 50.0’.

elevation-limit (float float) (default = unspecified)

Remove as outliers interest points whose height above datum (in meters) does not fall within this range. This can reduce the disparity search range.

corr-max-levels (integer) (default = 5)

The maximum number of additional (lower) resolution levels to use when performing integer correlation. Setting this value to zero just performs correlation at the native resolution.

xcorr-threshold (float) (default = 2.0)

Integer correlation to a limited sense performs a correlation forward and backwards to double check its result. This is one of the first filtering steps to insure that we have indeed converged to a global minimum for an individual pixel. The xcorr-threshold parameter defines an agreement threshold in pixels between the forward and backward result. See also --save-left-right-disparity-difference.

Optionally, this parameter can be set to a negative number. This will signal the correlator to only use the forward correlation result. This will drastically improve speed at the cost of additional noise.

min-xcorr-level (integer) (default = 0)

When using the cross-correlation check controlled by xcorr-threshold, this parameter sets the minimum pyramid resolution level that the check will be performed at. By default the check will be performed at every resolution level but you may wish to increase this value to save time by not doubling up on processing the largest levels.

Currently this feature is not enabled when using the default block-matching correlation method. In that case the cross correlation check is only ever performed on the last resolution level, which is level 0.

save-left-right-disparity-difference

Save the discrepancy between left-to-right and right-to-left disparities, defined as max(abs(left_disp_x - right_disp_x), abs(left_disp_y - right_disp_y)). Assumes a non-negative value of --xcorr-threshold and stereo algorithms asp_bm, asp_sgm, asp_mgm, or asp_final_mgm. Missing values are set to no-data. This is saved to <output prefix>-L-R-disp-diff.tif.

rm-quantile-percentile (double) (default = 0.85)

See rm-quantile-multiple for details.

rm-quantile-multiple (double) (default = -1)

Used for filtering disparity values in the low-resolution disparity D_sub.tif (Section 19). Disparities greater than quantile multiple times the quantile percentile (of the histogram) will be discarded. If this value is set greater than zero, this filtering method will be used instead of the method using the values rm-min-matches and rm_threshold. This method will help filter out clusters of pixels which are too large to be filtered out by the neighborhood method but that have disparities significantly greater than the rest of the image.

corr-timeout (integer) (default = 900)

Correlation timeout for an image tile, in seconds.

corr-blob-filter (integer) (default = 0)

Set to apply a blob filter in each level of pyramidal integer correlation. When the correlator fails it often leaves “islands” of erroneous disparity results. Using this blob filter to remove them cleans up the final stereo output and can even reduce processing times by preventing the correlator from searching at large, incorrect disparity amounts. The value provided is the size of blobs in pixels that will be removed at the full image resolution.

corr-tile-size (integer) (default = 1024)

Manually specifies the size of image tiles used by the correlator for multi-threaded processing. Typically there is no need to adjust this value but it is very important when using semi-global matching. See Section 18.2 for details. This value must be a multiple of 16.

sgm-collar-size (integer) (default = 512)

Specify the size of a region of additional processing around each correlation tile when using SGM or MGM processing. This helps reduce seam artifacts at tile borders when processing an image that needs to be broken up into tiles at the cost of additional processing time. This has no effect if the entire image can fit in one tile.

sgm-search-buffer (integer integer) (default = 4 4)

This option determines the size (in pixels) searches around the expected disparity location in successive levels of the correlation pyramid. A smaller value will decrease run time and memory usage but will increase the chance of blunders. It is not recommended to reduce either value below 2.

corr-memory-limit-mb (integer) (default = 6144)

Restrict the amount of memory used by the correlation step to be slightly above this value. This only really affects SGM/MGM which use a pair of large memory buffer in their computation. The total memory usage of these buffers is compared to this limit, and if it is greater then smaller search ranges will be used for uncertain pixels in order to reduce memory usage. If the required memory is still over this limit then the program will error out. The unit is in megabytes.

correlator-mode

Function as an image correlator only (including with subpixel refinement). Assume no cameras, aligned input images, and stop before triangulation, so at filtered disparity. See Section 16.17 for more details.

stereo-debug

A developer option used to debug stereo correlation.

local-alignment-debug

A developer option used to debug local epipolar alignment issues. An example is in Section 11.5.1.

17.3. Subpixel refinement

subpixel-mode (integer) (default = 1)

This parameter selects the subpixel correlation method. Parabola subpixel is very fast but will produce results that are only slightly more accurate than those produced by the initialization step. Bayes EM (mode 2) is very slow but offers the best quality. When tuning stereo.default parameters, it is expedient to start out using parabola subpixel as a “draft mode.” When the results are looking good with parabola subpixel, then they will look even better with subpixel mode 2. For inputs with little noise, the affine method (subpixel mode 3) may produce results equivalent to Bayes EM in a shorter time. Phase correlation (subpixel mode 4) is uses a frequency domain technique. It is slow and is best may not produce better results than mode 2 but it may work well in some situations with flat terrain.

Subpixel modes 5 and 6 are experimental. Modes 7-12 are only used as part of SGM/MGM correlation. These are much faster than subpixel modes 2-4 and if selected (with SGM/MGM) will be the only subpixel mode performed. They interpolate between the SGM/MGM integer results and should produce reasonable values. The default blend method for SGM/MGM is a custom algorithm that should work well but the you may find that one of the other options is better for your data.

Subpixel modes 1-4 can be used in conjunction with SGM/MGM. In this case subpixel mode 12 will be used first, followed by the selected subpixel mode. Depending on your data this may produce better results than using just the SGM/MGM only methods. You may get bad artifacts combining mode 1 with SGM/MGM.

0 - no subpixel refinement
1 - parabola fitting
2 - affine adaptive window, Bayes EM weighting
3 - affine window
4 - phase correlation
5 - Lucas-Kanade method (experimental)
6 - affine adaptive window, Bayes EM with Gamma Noise Distribution (experimental)
7 - SGM None
8 - SGM linear
9 - SGM Poly4
10 - SGM Cosine
11 - SGM Parabola
12 - SGM Blend

For a visual comparison of the quality of these subpixel modes, refer back to Section 11.

subpixel-kernel (integer integer) (default = 35 35)

Specify the size of the horizontal and vertical size (in pixels) of the subpixel correlation kernel. It is advantageous to keep this small for parabola fitting in order to resolve finer details. However for the Bayes EM methods, keep the kernel slightly larger. Those methods weight the kernel with a Gaussian distribution, thus the effective area is small than the kernel size defined here.

phase-subpixel-accuracy (integer) (default = 20)

Set the maximum resolution of the phase subpixel correlator. The maximum resolution is equal to 1.0 / this value. Larger values increase accuracy but also computation time.

17.4. Filtering

filter-mode (integer) (default = 1)

This parameter sets the filter mode. Three modes are supported as described below. Here, by neighboring pixels for a current pixel we mean those pixels within the window of half-size of rm-half-kernel centered at the current pixel.

The default is 1 for the full-resolution disparity, but mode 2 is hard-coded for filtering the low-resolution disparity D_sub.tif. Options:

0

No filtering.

1

Filter by discarding pixels at which disparity differs from mean disparity of neighbors by more than max-mean-diff.

2

Filter by discarding pixels at which percentage of neighboring disparities that are within rm-threshold of current disparity is less than rm-min-matches.

rm-half-kernel (integer integer) (default = 5 5)

This setting adjusts the behavior of an outlier rejection scheme that “erodes” isolated regions of pixels in the disparity map that are in disagreement with their neighbors.

The two parameters determine the size of the half kernel that is used to perform the automatic removal of low confidence pixels. A 5 × 5 half kernel would result in an 11 × 11 kernel with 121 pixels in it.

max-mean-diff (integer) (default = 3)

This parameter sets the maximum difference between the current pixel disparity and the mean of disparities of neighbors in order for a given disparity value to be retained (for filter-mode 1).

rm-min-matches (integer) (default = 60)

This parameter sets the percentage of neighboring disparity values that must fall within the inlier threshold in order for a given disparity value to be retained (for filter-mode 2).

rm-threshold (double) (default = 3)

This parameter sets the inlier threshold for the outlier rejection scheme. This option works in conjunction with rm-min-matches above. A disparity value is rejected if it differs by more than rm_threshold disparity values from rm-min-matches percent of pixels in the region being considered (for filter-mode 2).

rm-cleanup-passes (integer) (default = 1)

Select the number of outlier removal passes that are carried out. Each pass will erode pixels that do not match their neighbors. One pass is usually sufficient.

median-filter-size (integer) (default = 0)

Apply a median filter of the selected kernel size to the subpixel disparity results. This option can only be used if rm-cleanup-passes is set to zero.

texture-smooth-size (integer) (default = 0)

Apply an adaptive filter to smooth the disparity results inversely proportional to the amount of texture present in the input image. This value sets the maximum size of the smoothing kernel used (in pixels). This option can only be used if rm-cleanup-passes is set to zero.

texture-smooth-scale (float) (default = 0.15)

Used in conjunction with texture-smooth-size, this value helps control the regions of the image that will be smoothed. A larger value will result in more smoothing being applied to more of the image. A smaller value will leave high-texture regions of the image unsmoothed.

enable-fill-holes (default = false)

Enable filling of holes in disparity using an inpainting method. Obsolete. It is suggested to use instead point2dem’s analogous functionality.

fill-holes-max-size (integer) (default = 100,000)

Holes with no more pixels than this number should be filled in.

edge-buffer-size (integer) (default = -1)

Crop to be applied around image borders during filtering. If not set, default to subpixel kernel size.

erode-max-size (integer) (default = 0)

Isolated blobs with no more pixels than this number should be removed.

gotcha-disparity-refinement

Turn on the experimental Gotcha disparity refinement (Section 15.1). It refines and overwrites F.tif. See the option casp-go-param-file for customizing its behavior.

casp-go-param-file (string) (default = “”):

The parameter file to use with Gotcha disparity refinement when invoking the gotcha-disparity-refinement option. The default is to use the file share/CASP-GO_params.xml shipped with ASP.

17.5. Post-processing (triangulation)

near-universe-radius (float) (default = 0.0)

far-universe-radius (float) (default = 0.0)

These parameters can be used to remove outliers from the 3D triangulated point cloud. The points that will be kept are those whose distance from the universe center (see below) is between near-universe-radius and far-universe-radius, in meters.

universe-center (default = none)

Defines the reference location to use when filtering the output point cloud using the above near and far radius options. The available options are:

None

Disable filtering.

Camera

Use the left camera center as the universe center.

Zero

Use the planet center as the universe center.

bundle-adjust-prefix (string)

Use the camera adjustments obtained by previously running bundle_adjust with this output prefix.

min-triangulation-angle (double)

The minimum angle, in degrees, at which rays must meet at a triangulated point to accept this point as valid. It must be positive. The internal default is somewhat less than 1 degree.

max-valid-triangulation-error (double) (default = 0.0)

If positive, points with triangulation error larger than this will be removed from the cloud. Measured in meters.

point-cloud-rounding-error (double)

How much to round the output point cloud values, in meters (more rounding means less precision but potentially smaller size on disk). The inverse of a power of 2 is suggested. Default: \(1/2^{10}\) meters (about 1mm) for Earth and proportionally less for smaller bodies, unless error propagation happens (Section 14), when it is set by default to \(10^{-8}\) meters, to avoid introducing step artifacts in these errors.

save-double-precision-point-cloud (default = false)

Save the final point cloud in double precision rather than bringing the points closer to origin and saving as float (marginally more precision at twice the storage).

num-matches-from-disp-triplets (integer) (default = 0)

Create a match file with this many points uniformly sampled from the stereo disparity, while making sure that if there are more than two images, a set of ground features are represented by matches in at least three of them. The matches are between original images (that is, before any alignment or map-projection). The file name is <output prefix>-disp-<left image>__<right image>.match. This can be very slow for images 50,000 or more on the side. Use then num-matches-from-disparity. To not continue with triangulation, use --compute-point-cloud-center-only. See Section 12.2.1 for an application.

num-matches-from-disparity (integer) (default = 0)

Create a match file with this many points uniformly sampled from the stereo disparity. The matches are between original images (that is, before any alignment or map-projection). See also num-matches-from-disp-triplets.

compute-point-cloud-center-only

Only compute the center of triangulated point cloud and exit. Hence, do not compute the triangulated point cloud.

compute-error-vector

When writing the output point cloud, save the 3D triangulation error vector (the vector between the closest points on the rays emanating from the two cameras), rather than just its length. In this case, the point cloud will have 6 bands (storing the triangulation point and triangulation error vector) rather than the usual 4. When invoking point2dem on this 6-band point cloud and specifying the --errorimage option, the error image will contain the three components of the triangulation error vector in the North-East-Down coordinate system.

17.6. Error propagation (used in triangulation)

propagate-errors

Propagate the errors from the input cameras to the triangulated point cloud. See Section 14. This option implies --dg-use-csm for Maxar (DigitalGlobe) linescan cameras.

horizontal-stddev <double double (default = 0.0 0.0)>

If positive, propagate these left and right camera horizontal ground plane stddev values through triangulation. To be used with --propagate-errors.

position-covariance-factor <double (default: 1.0)>

Multiply the satellite position covariances by this number before propagating them to the triangulated point cloud. Applicable only to Maxar(DigitalGlobe) linescan cameras.

orientation-covariance-factor <double (default: 1.0)>

Multiply the satellite quaternion covariances by this number before propagating them to the triangulated point cloud. Applicable only to Maxar(DigitalGlobe) linescan cameras.

17.7. Bathymetry correction options

These are options are used to infer the depth of shallow-water bodies (see Section 8.27).

17.7.1. Pre-processing stage

left-bathy-mask (string)

Mask to use for the left image when doing bathymetry.

right-bathy-mask (string)

Mask to use for the right image when doing bathymetry.

17.7.2. Triangulation stage

bathy-plane (string)

The file storing the water plane used for bathymetry having the coefficients a, b, c, d with the plane being a*x + b*y + c*z + d = 0. Separate bathy planes can be used for the left and right images, to be passed in as ‘left_plane.txt right_plane.txt’.

refraction-index (double) (default = 0.0)

The index of refraction of water to be used in bathymetry correction. (Must be specified and bigger than 1.)

output-cloud-type arg (string) (default = all)

When bathymetry correction is used, return only the triangulated cloud of points where the bathymetry correction was applied (option: ‘bathy’), where it was not applied (option: ‘topo’), or the full cloud (option: ‘all’).

17.8. GUI options

See Section 16.64.15.