# Circular image block method

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## Jussi
Heikkinen

In this research a new method is developed for close range
photogrammetric measuring conditions. The novel method is designed for
conditions where object space is around the object and photogrammetric
measurements are to be done inside the object space.

- Multiple
images used in measurements
- Automatic
image measurements
- Approximating
for example tree stem volumes with cylinders.
- Best
measuring precision will be reached when using convergent images. This
can be gained by imaging two image sequences with opposite camera
orientations

This novel
method, which takes care of the imaging geometry as well as
constructing the whole model in a same coordinate system without any
additional coordinate transformations, is called the Circular Image
Block method. As in all image based measurements, position and
orientation of cameras respect to other camera poses must be known or
have to be determined in an estimation process. This guarantees
that the 3-D model determined by intersecting image rays from multiple
cameras will have correct shape and size. In case of stereo
imaging the cameras are installed to look in parallel and the distance
of projection centers along their common x-axis is determined through
calibration. But there are cases like aerial photography where
you only know the approximate pose and orientation of images. The
exact pose and orientation have to be determined by estimation.
In order to do that you have to measure at least three correspondent
points on images, where correspondent image points mean image points,
which are projections of the same 3-D point in object space. That
is the reason why subsequent images must partly overlap. Three
points are minimum for the mathematical solution as we have three pose
parameters and three orientation angles to be solved. From these
calculations we get the relational pose and orientation of cameras and
we can reconstruct the object in correct shape. After this only
the scale for object is still unknown. For the scale we have to
know at least one distance in object space. If in addition we
want to reconstruct the object in a particular coordinate system, we
also need to know three object points in that coordinate system.