If registration without altering the image is required, Spatial Transformation provides Register Image. For single order image transformations, Spatial Transformation provides Stretch Image.
A transformation is defined by a set of control points, matching positions on the image to the desired position on the map. From these points, a best n order polynomial is determined using a least squares fit.
This process is often called rubbersheeting because it is like placing the image on a rubbersheet, and pinning the sheet to the underlying map at known positions. The resulting image is much like what would occur as the rubbersheet stretched in various directions to accomodate the pins. The pins are the control points matching a position on the image to a position on the underlying map.
Warp Image provides interactive functionality to establish the control points. When the control points have been established, a button will open a dialog box which calculates the transformation. This transformation is applied to each input point and the distance between the transformed point and the desired position for that point (residual error) is calculated. Details for each point are shown.
In case a point has a very high residual error, and is likely to be in error, that point can be excluded from the transformation process. At least (n+1)*(n+2)/2 points are required to define an n-order transformation. However, using a larger number of points minimizes the effects of small errors in defining the points.
When satisfied with the residual errors, the new image is created. The World File parameters are set and the image is redrawn. The control points now reflect the new image.
Installation
Instructions
Warp Image can
be downloaded from www.spatial-online.com..
The file will be called WarpImage.exe.
In order to install Warp Image,
save WarpImage.exe to temporary space on your disk. Double click
it to run the install. An install wizard will appear to guide you through
the installation process.
To find Warp Image in
ArcView, activate the project window and from the file menu, choose Extensions.
In the Extensions dialog, click the box beside Warp Image. When a
view is open, a Warp Image menu item will appear to evoke Warp Image.
It will contain a link to this help.
The Warp Image menu will provide four choices:
To warp an image, open a view and add the shape files that are in the
vacinity of the image. Make the files active by clicking them in the View Table of Contents
and click the Zoom to Active Themes button.
Then add the image with View > Add Theme. In the bottom left corner of the dialog,
set the Data Source Types to Image Data Source. Choose your image and click OK.
Note that Warp Image only works with tiff files. Other files need to be converted
to tiff prior to warping. In case you choose another variety of image, you will be
able to register it, but not warp it.
Make the image visible by clicking the box beside its name in the ArcView Table of Contents.
Quite possibly, your image will not appear in the view. To make it centered in the current view:
The Warp Image menu label is changed to Warp name.tiff identifying
the name of the image your are Warping.
In addition to the control points, there will be two new buttons and two new tools.
There purposes are as follows: The labels on the screen must be dragged to appropriate positions for the rubbersheeting.
The precise position of the point is the bottom left corner of the box that is being dragged.
The aqua label must be dragged to a position on the image while the corresponding
yellow label is dragged to the corresponding position on the map.
For more accurate positioning,
you may wish to zoom in on each point.
Click the Z tool, then click near the control point of interest and the view will zoom
into the point.
Points can be deleted in the usual manner or added using the tool labeled A.
This transformation needs (n+1)*(n+2)/2 points.
However, specifying more than that avoids problems caused by slight
inaccuracies in the point input process.
In the example, six additional control points have been added.
Either click the W button or choose Warp Image > Warp Image
to warp the file.
When the product is running
in trial mode, the following registration screen will appear.
Clicking the purchase button
will evoke your browser with www.spatial-online.com
to enable you to purchase the product on-line, through the Fax or via Purchase
Order. When you purchase the product, you will be required to supply your
site code (just below the Purchase button - in the picture above it is 93613. It will be
different on your machine). In return, you will get a product
key. Insert that key into the Text Box next to Product Key and click OK
to purchase the product. Once you have done this, this registration box
will no longer appear.
To run the product in trial
mode, click the Run in Demo Mode button. Below the button, the remaining
trial period is shown.
Clicking the Cancel button
will stop the process.
The dialog below will appear.
The list box contains the labels for each point followed by the image column and row,
the map control position, the position that the image control was translated to, and the
residual error. The residual error is the distance between the desired position (the map control position) and
the translated position (where the image control position is moved to).
In case a point has a very high residual error, and is likely to be in error, that
point can be excluded from the transformation process by selecting it and then clicking
the Remove Point button. At least (n+1)*(n+2)/2 points are
required to define the transformation. However, using a larger number of points
minimizes the effects of small errors in defining the points.
If insufficient points are provided an error message will appear.
The buttons on the next line are the following:
In case the image is rotated, the corners of the resulting image will not
overlap the original image. There are three ways these can be assigned values:
The input image file and control point file are shown.
Beneath them is the name of the image file that will be produced.
This can be altered to any tiff file name that can be written.
If the Accept button has been clicked, once the new image is produced,
it will be positioned in the view using a World File.
The transformed image control points for the new image will be added to the view.
he initial image will made invisible and the new image will be the one that is currently active
for further modification.
Spatial Transformation offers other products for transforming data.
Warning: This computer program
is protected by copyright law and international treaties. Unauthorized
reproduction of it, or any portion of it, may result in severe civil and
criminal penalties, and will be prosecuted to the maximum extent possible
under the law.
The software comes "as is".
Neither Spatial Solutions Inc nor www.spatial-online.com make any
warranty, representation, promise or guarantee of any kind, either expressed
or implied, statutory or otherwise, including, but not limited to the implied
warranties of quality, performance, non-infringement, merchantability and
fitness for a particular purpose. The entire risk as to the quality and
performance of the software is with the user. We do not warrant that the
functions contained in the software will meet your requirements or that
the operation of the software will be uninterrupted or error free.
The last item will evoke this help in your default browser.
Prior to evoking Warp Image, control points need to be defined. The process is
started by clicking Warp Image > Initialize Control Points.
If you have previously built some control points for this image, you will be asked if you wish
to use the previous points. You can either choose Yes to utilize them, or No to start anew.
In case you do not have any control points, the system will start with four points at the four
corners of the image, labeled TL, TR, BL and BR. The image points are in aqua
and the map points in yellow such as seen in the screen below.
Label Position Purpose W Button Causes the image to be warped to the current control points Q Button Quits the registration process and clears the control points A Tool Adds a new control point Z Tool Zooms to closest control point
There is a choice of 0 to tenth order transformations. The default is first. In case the
image is to be shifted and scaled independently in the X and Y directions, and a new image
is not to be produced, the zero order transformation should be chosen.
Higher order transformations up to tenth order are available. For the higher order transformations,
it is very important that there are many control points. If there are insufficient, very small errors
in the control points can cause some unexpected results.
In addition, if the image can support transparency, you have the option
to Set transparent either of the white or black value that you chose.
The default is to assign these pixels to be
white, and, if the image can support transparency, to make them transparent.
You may also choose to color them black.
The third choice, giving each the value of the nearest
pixel in the image, works well for slight modifications.
However, for significant rotations, it produces a
streaky effect at the edges of the new image.
Return to Table
of Contents
Probably the order of transformation is too high, or the number
of control points is too low. For the higher order transformations,
it is very important that there are many control points. If there are insufficient, very small errors
in the control points can cause some unexpected results.
An n-order transformation needs (n+1)*(n+2)/2 points. However,
more than that are recommended. Specifying more points is likely to avoid problems caused by slight inaccuracies in the
point input process.
The control points should
be as regularly spaced throughout the data as possible. The four corners of the image
should be included.
In case the image is rotated,
the corners of the transformed image will not
overlap the original image. The default value for these pixels is the closest
pixel in the image. However, for significant rotations, this produces a
streaky effect at the edges of the new image. To avoid that effect, specify
a Default Pixel value to fill the undefined areas. Usually,
0 will result in a black fill and 255 in a white fill.
Other Spatial Transformation Products
Warp Image Copyright
©2000 is a product of Spatial Solutions Inc, dba Spatial Transformation. All rights reserved.