Locate world coordinate points
Locate world coordinate points
This option allows the specification of the world reference points. The
mapping function is set by [M Mapping function]. Every time the
option is entered, any new world reference points used will be added to the
list already in use. This list may be initialised (cleared) by [I
Initialise world coordinate mapping] and is stored in the
formatted file CalWldPt.DIG in the current directory. The list may be
editted manually.
Locate world reference points on which buffer ?
If (additonal) world reference points are being specified, then this must
occur using any valid buffer containing the necessary positional
information. Normally the user will have acquired previously the image to
be used into the buffer, which will be made the current output buffer.
Cursor Positioning: Locate world reference point
The DigImage cursor is used to locate the world reference points. These
will typically be picked up from some regular grid temporarily placed in
the experimental apparatus, or from some feature of the experiment or
apparatus of know dimensions. Operation of the cursor is in the normal
manner, with additional help available under the H help option within the
cursor submenu.
What are the real world coordinates of this point ?
In order for DigImage to be able to construct the necessary mapping, the
real world coordinates of the point located must be specified. The x and y
directions are arbitrary, but approximate alignment with the buffer lines
and rows is desirable. Two floating point values are expected.
Another world reference point ?
An affirmative answer (<Y> will return control to the cursor
submenu to allow a further point to be specified. A negative answer (<N>)
allows DigImage to continue to the function specification.
Mapping functions:
This selection submenu gives a choice of a range of different mapping
functions. The users choice should depend on the physical setup and the
expected relationship between pixel and real world coordinates. Typically
the simplest model consistent with the experimental situation should be
chosen as it will produce the most robust results. Further help is
available from the H help option within the submenu. Once the mapping
function type has been specified, DigImage evaluates the mapping using a
least squares fit to the world reference point data.
Parent menu
Main Menu
DigImage User Documentation
Stuart Dalziel,
last page update: 19 February 1996