DEMEDPREP

Name	Type	Length	Value range
InputDEM: Input elevation channel	DEM port	0 - 1	Default: 1
Input: Image layers *	Raster port	1 - 1024
Output: Vector-polygon layer *	Vec port	1 - 1024
Epipolar-image-selection method	String	0 - 1	PAIR \| MAXIMUM \| ALL \| OPT \| DENSE \| STRIPS \| AUTO \| TRI Default: PAIR
Minimum overlap (%)	Integer	0 - 2	0 - 100
Flight-line-break angle (deg)	Float	0 - 1

Parameter descriptions

InputDEM: Input elevation channel

The elevation channel to prepare for editing.The default value is 1.

DEMEDPREP verifies that the input channel has the required DEM-specific metadata tags. The required tags are:

ELEVATION_DATUM
ELEVATION_OFFSET
ELEVATION_SCALE
ELEVATION_UNITS
NO_DATA_VALUE
ELEVATION_BACKGROUND(deprecated and superseded by theNO_DATA_VALUEtag)

If any of the tags is missing or has an invalid value, processing stops, and an error message is displayed.

Input: Image layers

The raw images to process.

Output: Vector-polygon layer

The vector cutlines from the input images.

Epipolar-image-selection method

The method to use to form the epipolar pairs. The default isPair.

You can use any of the following supported values:

PAIR: automatically forms pairs according to the order in which the files are listed in the input folder or file. No other processing or screening of images is performed.
For example:
- File1 uses the left image for pair 1
- File 2 uses the right image for pair 1
- File 3 uses the left image for pair 2
- File 4 uses the right image for pair 2
MAXIMUM(Maximum): for each image, a single epipolar pair is created using the image that provides the most amount of overlap. If necessary, you can use theMinimum Overlap (%)(MINPC) parameter to specify the minimum percentage of overlap required to create a pair for consideration.
ALL: for each image, epipolar pairs are generated using all images that overlap above the value specified for the Minimum Overlap (%)(MINPC) parameter.
OPT(Optimum): epipolar pairs are generated to cover the entire project area, but an attempt is made to eliminate excessive duplication. The value of the Minimum Overlap (%)(MINPC) parameter is ignored with this method. Before pairs are selected, the images are assigned to contiguous flight lines, and only pairs of images from the same flight line are considered, to eliminate side overlaps. This method is intended for processing airborne images, where the concept of flight lines is well defined.
DENSE: epipolar pairs are generated to cover the entire project area, with every image used exactly twice: as a left image and a right image of adjacent pairs. The value of the Minimum Overlap (%)(MINPC) parameter is ignored with this method. Before pairs are selected, the images are assigned to contiguous flight lines, and only pairs of images from the same flight line are considered, to eliminate side overlaps. This method is intended for processing airborne images, where the concept of flight lines is well defined.
STRIPS: TheSTRIPSselection method uses the same concept as theDENSEselection method. But it groups the images into flight lines using their geographic data extents. TheSTRIPSselection method will only give good results if the flight lines are straight and parallel to each other.
The STRIPS method allows up to two values for the MINPC parameter:
1. Along-Track-MINPC: this applies between images within a flight line. If ommitted the default value is: 60
2. Across-Track-MINPC: this applies between images between different flight lines.
  If you provide only one value for MINPC, then it applies to the Along-Track-MINPC only and the Across-Track-MINPC is set to 100, effectively turning off across track pairing. This behavior is to maintain backwards compatibility with how the STRIPS method worked before the two values were introduced.
AUTO: TheAUTOselection method will use the best results from theSTRIPSandDENSEselection methods. It will use the selection method that generated the fewest flight lines.
TRI(Triple Stereo): this method is designed for triple-stereo images. It assembles them into triplets of Forward, Nadir and Backward looking images. Incomplete triplets, that is, pairs are also accepted, for example Forward and Nadir, in which case the data is treated as stereo rather than tri-stereo. The values of theMinimum Overlap (%)(MINPC) and Flight-line-break angle (deg) (BREAKANG) parameters are ignored with this method.

With the Max,All, Opt(Optimum), andDensemethods, you can specify additional options with a KEY=value. Each KEY=value pair must be preceded by a comma.

The following KEYs and their values are recognized:

SSL: Stereo separation lower limit, in degrees. Stereo separation is the angle between the lines of sight from the centroid of the image-overlap area to the positions of the two cameras or satellites. If SSLis specified, the pairs with stereo separation lower than the provided value are not formed. If the SSLkey is not provided or SSLorSSL= by itself is specified, the limit is set at 1(one degree). The value you specify must be greater than0degrees and less than180degrees.
SSU: Stereo separation upper limit, in degrees. If SSUis specified, the pairs with stereo separation higher than the value you specify are not formed. If the SSUkey is not provided orSSU or SSU= by itself is specified, the limit is set at 140degrees. The value you specify must be greater than0degrees and less than180degrees. If bothSSLand SSUare provided,SSL must be lower than SSU.
SAR: Specifies SAR-satellite-specific parameters to use in forming SAR epipolar pairs. You specify the parameters by using single-letter codes, and they can be provided as a contiguous string of letters that does not include the coma. The actual values are extracted from the metadata of each image. Candidate pairs are accepted if all specified SAR parameters match exactly; otherwise, the candidate pairs are rejected.
The following parameters (and the corresponding metadata tags) are recognized:
- N: Satellite platform name, provided by the PlatformName tag
- L: SAR look direction, provided by the LookDirection tag
- O: SAR orbit direction, provided by the OrbitDirection tag
- B: SAR beam mode (without beam number), extracted from the BeamMode tag
- P: SAR polarizations, provided by the Polarizations tag
- T: Product type, provided by the ProductType tag
The SARkey is evaluated only for the MaxandAll selection methods. SAR images without the required metadata tags are omitted from further analysis.

If SARorSAR= by itself is specified, all of the preceding parameters must be identical for two images to form a pair (that is, the default is equivalent to SAR=NLOBPT).If you specify only a partial list, the parameters included in the list must match for the two images to form a pair, and the parameters not included in the list are ignored.Special formsSAR=ALL andSAR=NONE are also recognized.The NONE option disables all checks, but ensures that only SAR (as opposed to optical) images are used in forming pair candidates.

CAUTION:
The pairs accepted according to the criteria provided in the SARkey are still screened according to their stereo-separation criteria defined by theSSL andSSUkeys. They must also satisfy the minimum-overlap percentage, as defined by the Minimum Overlap (%)(MINPC) parameter.

Minimum overlap (%)

The percentage of minimum overlap acceptable between two images for them to be considered a valid pair. The value you specify must be between0and100.

The default value is50(50 percent).

The first step in the pairing is to evaluate every pair to determine if the overlap is greater or equal to the value of this parameter. For each image pair,AandB, two overlap values are calculated:A/BandB/A.Pairs are rejected when the minimum ofA/BandB/Ais less than the valueMINPC / 100. The difference between the values A/B versus B/A is larger the more the two image sizes differ.

A/Bis the area ofArelative to the area ofB
B/Ais the area ofBrelative to the area ofA

Image Overlap Calculations

Example Overlap Scenarios:

Stereo image sets - examples1and2: when your data consists of stereo image sets, often forward and backward looking, you want only the stereo images to be paired together.In this case setMINPCto a high value, such as75or higher.For this example, the high value accepts the pairsABandCD, and rejects the pairsAC,AD,BC, andBD.
Non-stereo image set - example3: when your data consists of non-stereo image sets, similar to this example, you usually to pair images that are close to one another.In this case the default value value ofMINPCis often good. For this example, it produces the pairs:AB,AC,BC,BD, andCD.
Non-stereo image set - example4: for random images you want pair images might want to be less restrictive.In this case use a low value forMINPC, such as40.For this example, it produces the pairs:AB,AC, andBD.
Strips - example 5: when the images are organized into flight lines (strips) with differing along-track and across-track overlap. In this case use STRIPS SELMTHD wioth two MINPC values, such as 60,20.

Example Overlap Scenarios

CAUTION:

This parameter is ignored with some values of theSELMTHD(pair selection method) parameter.

Note: The MINPC parameter allows for two values. The second value is only used with the SELMTHD STRIPS, and is ignored for other selection methods. See the STRIPS method to understand how the first and second values are used to find epipolar candidates.

Flight-line-break angle (deg)

The break angle of the flight line, which is used to determine the end of a flight line. The vector angles between image centers are calculated, and if the vector angle between two image centers is greater than the break-angle threshold, this is determined to be the end of the flight line, at which point a new one begins. The default value is22.5(22.5 degrees).

CAUTION:

Use this parameter only when the selection method for epipolar pairs isOptimum(Opt) orDense.

This parameter is optional.

Details

DEMEDPREP prepares data for DEM editing in theDEM Editingwindow ofCATALYST Professional Focus.

The input image files must have a math-model segment to use to create epipolar pairs or triplets. The highest-numbered math-model segment of each file is used. If an image has no model, it is removed from processing. If fewer than two images with a math model are found during pair generation, processing stops, and an error message is displayed.Incomplete triplets, that is, pairs are accepted.

DEMEDPREP executes the following steps:

Ingest and verify all parameters per the description of each.
Create the output file in the input DEM geometry, and either copy or link the input elevation channel to it.
Generate a list of epipolar pairs or triplets from the raw images in the input file names, folder, or text file, according to the specified pair selection method.
Create a vector outline of each epipolar-pair or epipolar triplet data area.
Remove overlaps between all epipolar outlines.
For a selection method generating pairs, add the LeftImage and RightImage attribute to each polygon to identify the left and right image of each pair.
For theTriselection method, add the LeftImage, MiddleImage and RightImage attribute to each polygon to identify the left (forward), middle (nadir) and right (backward) image of each triplet.Missing images have empty attribute fields.
If necessary, reproject the resulting polygons to the output file geometry.
Create the output vector segment.
Store the resulting polygons in the output vector segment.

The output file will have at least one epipolar pair or triplet for each DEM pixel where the DEM and accepted image data overlap. After opening the data in theFocus DEM Editingwindow, the display will flicker between the left and right orthorectified images. These images will be created on-the-fly in the current editing area from the raw images and using the current DEM elevations. By iteratively adjusting the elevations in the window, and verifying the resulting orthorectified images, an accurate DEM can be produced quickly.

If the input elevation channel was linked to the output file, the in-place edited file containing the DEM can be used in further processing. If the input elevations were copied to the output file, the edited DEM in the output file should be used instead.

DEMEDPREP exits with an error if there is no overlap between the DEM area and the final cutline polygons.The output file is still created, and can be examined for any potential problems.

With theEpipolar-image-selection method(SELMTHD) parameter, you can select from a variety of selection methods, with theOptimum(Opt) andDensemethods designed specifically for airborne images:

Pair: automatically forms the pairs according to the order in which the files are listed in the input file names, folder, or text file. The number of generated pairs will be half of the number of images selected for processing, or one less for an odd number of images. If the available images are A, B, C, D, E, F, G, H, and I, the generated pairs will be AB, CD, EF, and GH. This selection method is intended for internal use, as in some cases it may result in gaps in the coverage of the project area.
Max:automatically forms the pairs that demonstrate the highest amount of overlapping. Use theMinimum-percentage overlap(MINPC) parameter to specify the minimumpercentage of overlap; pairs with overlaps below this percentage are not considered valid. The number of generated pairs will be equal to or slightly lower than the number of images selected for processing. If the available images are A, B, C, D, E, F, G, H, and I, the generated pairs will be AB, BC, CD, DE, EF, FG, GH, and HI, provided all pairs meet the minimum-overlap criteria.
All:automatically forms all pairs that overlap above the specified value of theMinimum-percentage overlap(MINPC) parameter. The number of generated pairs may be several times higher than the number of images selected for processing, depending on the image spatial layout and the specified value of theMinimum-percentage overlap(MINPC) parameter.
Optimum(Opt:) automatically assigns images into spatially contiguous flight lines, and within each flight line selects pairs that provide full coverage of the flight-line length, with maximum overlap within each pair. The number of generated pairs will not exceed the number of images selected for processing, and in some cases may be less than half of the number. Provided that the available images constitute two flight lines, with images A, B, C, D, E, and F in the first line, and G, H, I, and J in the second line, the generated pairs may be AB, DE, and EF for the first line, and GH and IJ for the second line. The first and last pairs of each flight line are always generated, and no pairs are created from images belonging to different flight lines.
Dense:automatically assigns images into spatially contiguous flight lines, and within each flight line selects all pairs with maximum overlap within each pair. The number of generated pairs will be the same as or slightly lower than the number of images selected for processing. Provided that the available images constitute two flight lines, with images A, B, C, D, E, and F in the first line, and G, H, I, and J in the second line, the generated pairs will be AB, BC, CD, DE, and EF for the first line, and GH, HI, and IJ for the second line. This method is similar to theMaxmethod, except the images are divided into flight lines and no pairs are created from images belonging to different flight lines.
Tri:this method is designed for tri-stereo data, such as ZY-3, Gokturk-1, and ADS.It assembles image triplets from the forward, nadir and backward views of the same area on the ground.Each image in the tri-stereo dataset must contain the metadata tag named"LookDirection"with values"forward","nadir"or"backward".In this method theMINPCandBREAKANGparameters are ignored, and the optional KEY=value pairs are not supported.

You can further refine the selection criteria by using the optional KEY=value pairs. You can use the lower and upper values of stereo separation for theMax,All, Optimum(Opt), andDensemethods. For example, to restrict theDensepair-selection method to the range of convergence angles from 20 degrees to 40 degrees, specify the value of theEpipolar-image-selection method(SELMTHD) parameter as"DENSE,SSL=20,SSU=40".

TheSARkey is specific to satellite-SAR images, and is evaluated only for theMaxand Allmethods.Typically, all of the parameters are used and, therefore, it is sufficient to specify the SAR keyword by itself, for example"MAX,SAR,SSL=5,SSU=20".The non-default settings should be used only in rare circumstances and for well-understood data, so that undesirable pairs are not formed.

Note: This algorithm is available only in canvas mode.

Environments	PYTHON :: EASI :: MODELER
Batch Mode	Yes
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DEMEDPREP

Prepare a DEM for manual editing

Description

Parameters

Parameter descriptions

Details