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NAME

i.points.auto

DESCRIPTION

This module allows a search of GCP's on two raster-maps with differents levels of automation.

The manual search is the default search, so it's possible to determine the GCP's manually with the mouse.

Semiautomated-search

You have to determine with the mouse some corrispondent areas (with a discrete precision) in the two maps and the module searches the GCP's in these areas.

Automated-search

At the start of module you have to load the maps that the algorithm uses to the search, so it's recommended to use the maps filtered with the filters DIVERSITY or STDDEV (of GRASS) with a window of 3x3 or 5x5 pixels. However, the algorithm sometimes work well with the original maps too.

You click the button Automated-Search and then you have to load the maps that you want to visualize at the end of the search (with the GCP's), usually they are the original maps.

If the maps have strong geometric distortion and strong geometric differencies, maybe the results of the search (with the default options) are not good, so you can click the button LESS-GCP's and then repeat the operation.

The Overlap-Points (O.P.) era two corresponding points (one for every maps) that is used from the algorithm to determine the overlapping-area in the two maps. The Master-map is considered the map on the left, and the Slave-map is the map on the right.

Center, top, bottom, left, right are the position of the Master Overlap-Point (on the left map) that will be searched on the Slave map (right map). Center is the point at the center of the map. Top, bottom, left, right are the position of the O.P. respect to the center of the map. If you choose one of these possibilities, then you have to choose the shift from the center, measured in percentage of the dimensions of the map; there are two possibilities: 5% and 10%. This type of search is the most automated (fully-automated ).

If you choose -MARK SLAVE O.P.-, then the module visualizes a blue point at the center of the master map, and you have to mark the corrispondent point on the slave map. You can use this function if the maps are overlapped for more of 50% and if the algorithm doesn't have success in the fully-automated search.

If the maps have a overlapping area less of 50%, you can use the function -MARK M and S O.P.-. You have to mark a point in the master map and the corresponding point on the slave map.

At the end of search it's possible to exclude automatically the points not really corresponding. This function use the rms with a threshold. The default-value for the threshold is 2.5, but (before to active the Auto-Exclusion) you can change it, chossing one of different proposed values; you can choose an arbitrary value with click on -OTHER-, so you go on the shell and digit the value from keyboard and confirm with ENTER.

SEE ALSO

i.points, i.vpoints, i.rectify, i.group modules

AUTHORS

Based on i.points by Michael Shapiro, U.S.Army Construction Engineering Research Laboratory
additions by Ivan Michelazzi, Luca Miori (MSc theses at ITC-irst)
Supervisors: Markus Neteler, Stefano Merler, ITC-irst 2003, 2004

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