Compute homologous points between images using keypoints
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.
This section describes in details the parameters available for this application. Table 4.90, page 633 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 |
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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 |
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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
To run this example in command-line, use the following:
To run this example from Python, use the following code snippet:
Full mode does not handle large images.
This application has been written by OTB-Team.
These additional ressources can be useful for further information: