Using Digitizer 1.3

In this tutorial we review some of the details of using the Digitizer program. The purpose of Digitizer is to digitize a graph or image with an xy-coordinate system. The parts of Digitizer are

1. Entering an image.
2. Making the coordinate system.
   1. Setting the origin.
   2. Setting x and y base points.
   3. Defining the scale factors.
   4. Pixel error
3. Entering points on the image.
4. Finding length and area.
5. Showing data and exporting data.
6. An EXCEL trick - parsing data.

The program itself, with an image loaded and point selected, looks like the picture below.

Entering an image

There are several ways to enter the file name. In the example above, we have entered the file "circle.jpg." In all cases you will need to import JPG (or JPEG)

images.

Method 1. The first and easiest is to browse for the file on your local hard disk. Press the browse button and you will be able to navigate around in the folders on your hard disk. When you have found the desired files, select it, and then press the Load Image button. Occasionally, it is necessary to press the Load Image button twice.

Method 2. Type into the image input box the complete path name of the image file name. Then choose Load Image.

Method 2. With your browser find the file and be certain that is given by a URL. Copy the complete URL into the image input box and choose Load File.

You can modify the file in three ways:

• Move picture: Choose the "Move picture" button. Then click on and drag the image where you wish it to be. Alternatively you may simple select the image and move it to the desired position. Remember, the move picture feature is disabled when select origin button is chosen.
• Rotate the image: This feature will rotate the image 90⁰ counterclockwise. Warning: You may need to use the Move picture option after rotating to reposition the image.
• Scale to: By inserting any positive number and choosing the scale to button the image will be re-sized to what every percentage is entered. The aspect ratio of the image is retained. Therefore you will be able to load both very small and very large images and work with them. You can also scale up by 10%, scale down by 10% or reset the image to its original size and location.

Requirements: The file must be a jpg or a swf file.

Making the coordinate system

There are three steps to making the coordinate system.

1. Choose the "Select origin" button and drag the origin to where you wish it to be and release the mouse button. You can always re-select the "Select origin" if you want to change its position.
2. Choose the "Select point on x-axis button" and drag it to the horizontal position to set your scale. In the box next to it select what value on the x-axis this point should have. The default value is one. Don't worry about the vertical positioning of this point as it will not affect the result. You must choose this value. Otherwise there is no defined scale for a coordinate system.
3. Choose the "Select point on y-axis button" and drag it to the vertical position to set your scale. In the box next to it select what value on the y-axis this point should have. The default value is one. Don't worry about the horizontal positioning of this point as it will not affect the result.   
     Caution, if you do not enter the "Select point on y axis" button, the vertical scale will be the same as the horizontal.

Entering points on the image - showing the data

The is the only tricky part. Choose the "Select points" button. Position the cursor near where you wish to digitize a position on the image. Then depress and hold the left mouse button while you drag the point into place. You will not see the point until you begin to drag it.

This is important. Each point requires a few pixels of dragging to become active. This allows you precision positioning of your data.

In general, all points are accurate to within 2% of their positioning. A limit of 50 points can be entered.

Options available to you include clearing all points and removing the most recent point drawn, according to the self-evident buttons.

After you have selected the "Select Points" button, you will see the message change to "Show data." Pressing this button will result in the display of the digitized data points that you've created.

Pressing the "Show data" button will result in the scaled data points to be displayed

Having selected this button the message changes again to "Add more points." Pressing this button allows you to continue adding points as above. The limit of the number of points is about 45.

Pixel Error. Upon selecting the Show data button, the per pixel errors in the x and the y directions are shown. The information gives the error incurred by selecting the data point just one pixel to the right or left, up or down. It should give some measure of what kind of error to expect.

Finding length and area

At any time after selecting two points or more you may select the length or area buttons to obtain the length or area of the curve up to the current point. The scale factors for the x-axis and y-axis are used in these calculations. You may continue to add points. Thus length and area can be determined without exporting the data to a spreadsheet. In the example below we have computed the area and perimeter of an equilateral triangle.

In the example below we determine the mileage along a piece of countryside near Elgin, TX beginning at Blue, TX. Please note that the origin and x axis point were placed in the top right on the scale for the map. Also, the x axis value was chosen to be 5. This then calibrates our measurements. This is OK since we are interested in distance between points and not the points themselves. Naturally accuracy improves with more points.

Remember, if you do not enter the "Select point on y axis" button, it is assumed that the horizontal and vertical scales are the same.

Pixel Error. Upon selecting the Length or Area buttons, the per pixel errors in the x and the y directions are shown. The information gives the error incurred by selecting the data point just one pixel to the right or left, up or down. It should give some measure of what kind of error to expect.

Showing data and exporting data

After you have created your points, you can display them by choosing the "Show points" button, which is the same button used for choosing to select points. The newly digitized points are display in the box as shown above. This set of points can be copied and pasted into your spreadsheet of word processor for further calculations and other work.

If you have missed point that you wish to digitize you can then choose "Add more points" and continue building your data. The show points and the new data will be appended to the old data.

Toggling spaces or commas. You may also choose to display the data with only a space between coordinate pairs. Do this by selecting the "Spaces between" button. Selecting the button again will switch back to the commas between mode.

	Left: Set for commas between
	Right: Set for spaces between

An EXCEL trick

When you paste this data into EXCEL it will display in just one column of the spreadsheet. This makes calculations impossible. However it is possible to parse the data in the following way. Suppose the data from the Digitizer is pasted into EXCEL as shown below.

 

This data can be parse into two columns by the following trick. Highlight the data. In EXCEL choose the Data+Text to Column option. You will obtain the following menu. Be sure the "Delimited" button is selected. Click next

Now select Finish. The data will be parsed into two columns as shown below, and ready for calculations.

Technical

Digitizer 1.14 is a complete Internet based digitizing software that should run on any browser with the Flash Player. The features of the software will allow any JPEG image or SwF movie to be loaded, a coordinate system (i.e. origin) defined, points on the x-axis and y-axis specified, and points selected.
(URL: http://www.macromedia.com/software/flashplayer/)