digitize

Matlab tool for digitizing images

DIGITIZE: Image Digitization Tool

Description:

digitize is a user interfase that allows
to import image files (.bmp, etc) into MatLab
to digitize data from. Previous sessions can
also be loaded.

Intructions:
First load a new image by entering the menu "Load"
and clicking on "Load New Image".
First the Referennce Points (points on the image whos
coordinates are known) must be selected.
This is done by entering the "Transformation" menu
and then selecting "Add Points".
Left-click on the points reference points and Right-click
when finished. Then Right-click on any reference point to enter it's "true" coordinate. When the coordinated for all the reference points have been entered the "Reference Data Complete" is checked inside the "Transformation" menu. To digitize, select "Add Points" from the "Digitization" menu. You may start digitizing points on the image at any time, but their transformed coordinated are not calculated until the reference data is complete. To see a digitized point's transformed coordinate, right-click on a point.

A session .mat file contains:
jt,kt - reference points in image axes coordinates
xt,yt - reference points in transformed coordinates
img - the RGB 'Cdata' of the image
jd,kd - digitized points in image axes coordinates
xd,yd - digitized points in transformed coordinates
R - the transformation matrix
The transformation matrix is used to convert from
the image axes coordinate system to the desired
coordinate system by entered the "true" of transformed
coordinates manually.

The first order linear transformation matrix is:
R = [sx ry 0;...
ry sy 0;...
tx ty 1]
where s -> scaling, r -> rotation, t -> translation

A second and third order fits are also available in the
"Transformation" menu. These are useful for distorted images or maps of unknown projection. The drawback is that larger orders requiere more data.

Click on "Residuals" in the "Transformation" menu
to see the residuals of the reference points.
The residuals are defined as the "true" or "given"
value minus the calculated value using the transformation
matrix. The residuals should be of the order of magnitude
of the pixcel size.

The pixcel size can be seen by clicking on
"Pixcel Size" in the "Transformation" menu.
The pixcel size is the horizontal x vertical direction.
Note that these are approximate because the
image is assumed to be rotated.

The directory is automatically changed to the directory of the image file.

An image can be loaded directly by using for example:
digitize('ImageFileName.bmp')