Lesson 2. Eliminating distortions using
calibration, setting up UCS,
Brief
description: During this lesson you will learn how to set up
a User Coordinate System (UCS), save a WiseImage document, and eliminate
distortions of a raster image using calibration.
 For detailed information on these subjects see the following sections
of the Quick Start guide:
Document Coordinate System, Saving WiseImage Document, Eliminating
linear and non-linear distortions using calibration.
How to set up UCS
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How to set up scale:
- In the Coordinate System tab press the Measure
Scale button, and then specify on screen a length for
a grid cell. The measured distance appears in the On Page
field.
- Enter this distance (100 mm) in the Actual field.
- Press Apply.
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How to set up origin:
- In the Coordinate System tab, press the Measure
Origin button, then specify the bottom-left grid node
on the raster image.
- In the To field specify the actual coordinate
of the bottom-left grid node: 200, 200.
- Press OK.
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Calibrating a raster image
Calibration is used to eliminate arbitrary (both linear
and non-linear) distortions of raster images.
The original image must contain points with known coordinates.
These points are called real points. You can use nodes of a rectangular
grid as real points (if you work with mapping materials) and/or other
points, whose coordinates are known or can be calculated.
The points, which correspond to the real ones on the distorted
image are often located with some displacement. These points are called
measured points, as their coordinate value can be measured on the
raster image.
The purpose of calibration is to transform the raster
image so that the measured points coincide with or are extremely close
to the real points.
Choose Open from the File
menu. Open the Utrecht.cws document from the
Lesson_2-3 folder, which was created and saved during
the previous exercise.
- Choose Calibration from the Image menu.
Define real points
You can use the rectangular grid nodes as real points
on this image.
A grid is defined by three parameters: start point
(coordinates of bottom-left node), sell size (by X and Y axis), and grid
size (by X and Y axis).
Define the calibration grid:
- Press the Define grid
 button
of the Calibration dialog. Specify the following parameters:
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Origin - coordinates of the bottom-left
node - 200,200
Cell -cell size: X Size -100, Y Size -100
Size -grid size: X Cell - 2, Y Cell - 2
- Press the Preview button to make sure the grid
was defined correctly.
- Press OK.
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Specify measured points
- Press the Next Point
button of the Calibration dialog. WiseImage places
the first point from the list in the screen center (point 1) and
highlights it with grips.
- Move the grips to the grid node on the scanned image (in point
2) - in doing so you specify the measured point.
- Press N (next) to move to the next calibration
pair. (P (previous) - to move to the previous one).
Specify the measured points for all real points from the list.
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Choose a calibration method
- From the combo-box of Calibration Method select
Choose automatically or, if needed, another calibration
method from the list. Evaluate the error of the selected method
by pressing the Estimate
button.
- Press Apply.
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Saving a WiseImage Document
- Choose Images from the Tools menu.
- In the Image Manager dialog specify a way to store the
raster image - either in a separate file or embedded in the document
file. If you want to save it embedded - press the Embed
 button.
Close Image Manager.
- Choose Save As from the File menu. From
the Save as type list choose Color Workspace File (*.cws).
- Press the Save button to save the Utrecht.cws
document in the Lesson_2-3 folder.
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