DSMMERGE

Description

DSMMERGE is used to merge (multi-angle) geocoded DSMs that were typically produced by EPIPOLARDSM and geocoded using GEOCODEDEM. Imagery associated with the geocoded DSM can be colour balanced and simultaneously merged at the same time producing a rough ortho image co-registered with the DSM.

Parameters

dsmmerge(mfile, dbec, dbscore, dbimage, filo, edgefix, demfilt, demopts)

Name	Type	Caption	Length
MFILE *	str	List of geocoded DSM files to merge	1 -
DBEC *	List[int]	Input DSM (elevation) channel	1 - 1
DBSCORE	List[int]	Input score channel	0 - 1
DBIMAGE	List[int]	Input Image channels	0 - 8
FILO *	str	File name of output DSM	1 -
EDGEFIX	List[int]	Edge Fixing Filter Sizes	0 - 16
DEMFILT	str	Filter level	0 -
DEMOPTS	str	Merging options	0 -

* Required parameter

Parameter descriptions

MFILE

List of geocoded DSM files, typically produced by GEOCODEDEM as part of a DSM extraction process from stereo imagery. This can be a directory, a directory with wild card or a list of file names held in a text file (.txt extension). All files must have the same projection, resolution and band sequence.

DBEC

Specifies the input band (channel) that contains the digital elevation model (DSM or DEM) to be used.

DBSCORE

Optionally specifies the channel that contains score information. Typcially this is a mask that shows valid DSM values, failed DSM locations, and No Data pixels.

If a negative value is specified then this indicates a (postive) score band exists and should be used however it should not be written to the output file.

NOTE: If a score band is available the resulting merged DSM is typically of higher quality.

DBIMAGE

Optionally specifies the imagery channels that should be merged to create a rough image overlay to the DSM. These are assumed to be bands already in each geocoded DSM file.

FILO

The name of the output file. A file with the same name must not exist in the output folder. The file will be created with the same projection and resolution as using the first file specified in MFILE. The first output band will be the DSM followed by imagery (if specified) and the score (if specified) in the last band.

EDGEFIX

Specifies the size of the filter used to clean up building and tree edges. If unspecified then a value of 13 is used. Specifying a value of 0 switches off this option.

DEMFILT

The level of filtering to apply to the generated DSM. The process applies successive noise, median, and smoothing filters.

The available values are as follows:

NONE: applies no filtering, but fills holes.
LOW: applies minimal filtering and provides greatest detail, but the surface will be rougher.
MEDIUM: applies moderate filtering to balance detail and smoothness.
HIGH: applies the maximum filtering and smoothing, but with less detail.

You can apply a custom filter by specifying any of the following:

nl,nm,nh: a light (l), medium (m), or heavy (h) noise filter.
m=#: enter a value for the number sign (#) to specify the size of a median filter.
h=#: enter a value for the number sign (#) to specify the size of a hybrid median filter. This filter preserves building corners.
s=#: enter a value for the number sign (#) to specify the size of a (Gaussian) smoothing filter.
b=#: enter a value for the number sign (#) to specify the size of a bi-level-smoothing filter. This filter prevents blurring of building edges.

Regardless of the order you specify, DSMMERGE applies filtering in the following order:

Noise
Median
Smoothing

A typical example of a filtering application is as follows:

"nm h=5 b=3"

The preceding applies a medium noise filter, a hybrid 5 x 5 median filter, and a 3 x 3 bi-level-smoothing filter.

Note: If you specify a filter that is not in the preceding list, such as k=23, it is ignored.

DEMOPTS

Specifies special processing options. Typically, you need not specify a value for this parameter.

The options are:

balance: colour balances the imagery (if supplied via DBIMAGE parameter). This applies permanent changes to the imagery in each file.
gapfill: Fill small nodata gaps in the DSM. Usually used if DSM tiles, with no or very little overlap are being assembled into a final mosaic.
speckle: switches off speckle filtering in the imagery (if supplied via DBIMAGE parameter).
blend=#: specifies the blending width between DSMs from different files. Default is 48. Maximum is 200. A value of 0 switches off blending.

Tip: You can specify more than one option, with each separated by a blank or comma.

Return Value

Returns: Number of images used.

Type: PCI_INT

The return value is the number of input images used to fill the output image.

Details

DSMMERGE merges a set of geocoded DSM's from a stereo airphoto or satellite project into a single DSM. The merged DSM is typically of higher quality since each geocoded DSM has a different viewing geometry and occlusion in one DSM can be filled in from a different DSM. In addition the multiple DSM elevations of the same ground pixel can be used to detect blunders and averaging multiple good elevations can increase vertical accuracy.

A score band (DBSCORE) can be specified (if available) to increase reliability of the merging process by specifying which DSM values are 'good' or 'failed'. Failed pixels are not used in the merged DSM. If a score band is not specified then an attempt is made to reject DSM values that do not match with the majority of the other DSM values at a particular location. A score value of 0 indicates a failed pixel, 255 indicates no data and values between 90 and 110 indicate a good pixel (100 default).

If imagery is available (DBIMAGE) this this will be merged together at the same time as the DSM values. The resulting image will be a 'crude' true-orthorectification (aka DSM ortho) product however it is not colour balanced by default and will contain many rough building edges. This imagery is intended to provide guidance in further DSM editing or a rough pre-view of the higher quality product that can be generated using the TORTHO algorithm. The imagery can be colour balance by specifying the 'balance' option in the DEMOPTS parameter. If this option is specified a temporary working directory is created in the same directory as the output (FILO). This processing can take significant temporary disk space equivalent to two times the total disk space of the all the imagery bands. The final colour balancing is applied directly and permanently to the imagery in each input DSM file so should only be used once.

The EDGEFIX parameter attempts to straighten building edges in the DSM by applying a filter. Larger filter sizes will do a better job on long straight buidling edges but may have unintended consequences on buildings with curved or complex edges. While building edges are the intended target this filter will also affect trees and cliff edges. If the DSMs do not contain buildings smaller values (or switching this option off) is recommended. Values from 5 to 31 are supported and the default is 13. A value of 0 switches this option off.

The typical workflow is as follows:

Create epipolar DSM's by running EPIPOLARDSM with no or low filtering
Geocode the epipolar DSM's by running GEOCODEDEM
Merge the Geocoded DSM's by running DSMMERGE

Other DSM merging methods are available, but are used in slightly different circumstances. SGMMERGE is intended to merge Forward/Nadir (F/N) and Backward/Nadir (B/N) pairs of images in the nadir epipolar space followed by geocoding via GEOCODEDEM. MOSPREP and MOSRUN can take sets of geocoded DSMs but use a 'cookie-cutter' approach and does not compensate for occlusions and building leans etc...

The input files must contain the same number of channels, and have the same projection and resolution.

Example

You have a set of overlaping geocoded DSM's created from an airphoto project in (c:\\project\\*.pix. All files have the same projection and resolution. In each file band 1 contains the DSM, bands 2,3,4 contain RGB imagery and band 5 is the score band. Since the DSMs produce do not perfectly align vertically due to small errors in the exterior orientation a larger blend width of 100 is used (instead of the default of 48):


from pci.dsmmerge import dsmmerge

mfile      = "project/*.pix"
dbec       = [1]
dbscore    = [5]
dbimage    = [2,3,4]
filo       = "merged_dsm.pix"
edgefix    = [9]
demfilt    = "medium"
demopts    = "blend=100"

dsmmerge(mfile, dbec, dbscore, dbimage, filo, edgefix, demfilt, demopts)

Environments	PYTHON :: EASI
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DSMMERGE

Merge (multi-angle) geocoded DSMs to create a single output DSM mosiac

Description

Parameters

Parameter descriptions

Return Value

Details

Example