4.6.7 Homologous Points Extraction

Compute homologous points between images using keypoints

Detailed description

This application allows computing homologous points between images using keypoints. SIFT or SURF keypoints can be used and the band on which keypoints are computed can be set independantly for both images. The application offers two modes : the first is the full mode where keypoints are extracted from the full extent of both images (please note that in this mode large image file are not supported). The second mode, called geobins, allows one to set-up spatial binning to get fewer points spread across the entire image. In this mode, the corresponding spatial bin in the second image is estimated using geographical transform or sensor modelling, and is padded according to the user defined precision. Last, in both modes the application can filter matches whose colocalisation in first image exceed this precision. The elevation parameters are to deal more precisely with sensor modelling in case of sensor geometry data. The outvector option allows creating a vector file with segments corresponding to the localisation error between the matches. It can be useful to assess the precision of a registration for instance. The vector file is always reprojected to EPSG:4326 to allow display in a GIS. This is done via reprojection or by applying the image sensor models.

Parameters

This section describes in details the parameters available for this application. Table 4.90, page 631 presents a summary of these parameters and the parameters keys to be used in command-line and programming languages. Application key is HomologousPointsExtraction.





Parameter key

Parameter type

Parameter description




in1

Input image

Input Image 1

band1

Int

Input band 1

in2

Input image

Input Image 2

band2

Int

Input band 2

algorithm

Choices

Keypoints detection algorithm

algorithm surf

Choice

SURF algorithm

algorithm sift

Choice

SIFT algorithm

threshold

Float

Distance threshold for matching

backmatching

Boolean

Use back-matching to filter matches.

mode

Choices

Keypoints search mode

mode full

Choice

Extract and match all keypoints (no streaming)

mode geobins

Choice

Search keypoints in small spatial bins regularly spread across first image

mode.geobins.binsize

Int

Size of bin

mode.geobins.binsizey

Int

Size of bin (y direction)

mode.geobins.binstep

Int

Steps between bins

mode.geobins.binstepy

Int

Steps between bins (y direction)

mode.geobins.margin

Int

Margin from image border to start/end bins (in pixels)

precision

Float

Estimated precision of the colocalisation function (in pixels).

mfilter

Boolean

Filter points according to geographical or sensor based colocalisation

2wgs84

Boolean

If enabled, points from second image will be exported in WGS84

elev

Group

Elevation management

elev.dem

Directory

DEM directory

elev.geoid

Input File name

Geoid File

elev.default

Float

Default elevation

out

Output File name

Output file with tie points

outvector

Output File name

Output vector file with tie points

inxml

XML input parameters file

Load otb application from xml file

outxml

XML output parameters file

Save otb application to xml file











Table 4.90: Parameters table for Homologous Points Extraction.

Input Image 1 First input image

Input band 1 Index of the band from input image 1 to use for keypoints extraction

Input Image 2 Second input image

Input band 2 Index of the band from input image 1 to use for keypoints extraction

Keypoints detection algorithm Choice of the detection algorithm to use Available choices are:

Distance threshold for matching The distance threshold for matching.

Use back-matching to filter matches. If set to true, matches should be consistent in both ways.

Keypoints search mode Available choices are:

Estimated precision of the colocalisation function (in pixels). Estimated precision of the colocalisation function in pixels

Filter points according to geographical or sensor based colocalisation If enabled, this option allows one to filter matches according to colocalisation from sensor or geographical information, using the given tolerancy expressed in pixels

If enabled, points from second image will be exported in WGS84

Elevation management This group of parameters allows managing elevation values. Supported formats are SRTM, DTED or any geotiff. DownloadSRTMTiles application could be a useful tool to list/download tiles related to a product.

Output file with tie points File containing the list of tie points

Output vector file with tie points File containing segments representing matches

Load otb application from xml file Load otb application from xml file

Save otb application to xml file Save otb application to xml file

Example

To run this example in command-line, use the following:

otbcli_HomologousPointsExtraction -in1 sensor_stereo_left.tif -in2 sensor_stereo_right.tif -mode full -out homologous.txt

To run this example from Python, use the following code snippet:

#!/usr/bin/python 
 
# Import the otb applications package 
import otbApplication 
 
# The following line creates an instance of the HomologousPointsExtraction application 
HomologousPointsExtraction = otbApplication.Registry.CreateApplication("HomologousPointsExtraction") 
 
# The following lines set all the application parameters: 
HomologousPointsExtraction.SetParameterString("in1", "sensor_stereo_left.tif") 
 
HomologousPointsExtraction.SetParameterString("in2", "sensor_stereo_right.tif") 
 
HomologousPointsExtraction.SetParameterString("mode","full") 
 
HomologousPointsExtraction.SetParameterString("out", "homologous.txt") 
 
# The following line execute the application 
HomologousPointsExtraction.ExecuteAndWriteOutput()

Limitations

Full mode does not handle large images.

Authors

This application has been written by OTB-Team.

See also

These additional ressources can be useful for further information: