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Model Building

Simple Example



1.)  The much misunderstood and over used term "model" is used in the field of remote sensing to refer to a series data transformations steps which will result in a new image that depicts or estimates the desired outcome. That is to say, that most "remote sensing" models are deterministic (a model in which there are no random events) and have the goal of data reduction, calibration, or estimation.

Begin by creating a very simple model. First select the MODELER icon from ERDAS icon menu .

The following menus will be displayed. Select the Model Maker option

(2) Drag the modeling "objects" from the tool bar on the left into the modeling window. Include the arrows that connect the objects

Now double click on the "input image object" in the upper left (or click once and then select the properties from the edit menu). The dialog box will be displayed which can define that model object. Provide the file name for the input image (pnw98_bbc.img). Go ahead and define the "output image object" in the lower right. Give it any name you wish (remember to direct the output to the sub-directory you want).

Now double click on the "function model object" (the circle in the middle). This object allows you to define the transformation process for this step in the model. We'll do something very simple. Divide band 4 of the input image by band 3.

Before we run the model let's document the model. Select the icon from the tool bar and add text to the model window.

(3) Now run the model by selecting the from the model window icon menu. When completed display the results in a viewer.

save the model if you wish. Otherwise close the model make window.


4.) Now let's look at a model which is a bit more complex. The Normalized Difference Vegetation Model (NDVI) is often used to depict the "vigor" of vegetation. While we can discuss the merit of such a model the equation for the model is simply

ERDAS (like most image processing softwares) has a built in option for producing common models or indices. Select the Indices option from the Spectral Enhancement menu available from the Image Interpreter icon on the ERDAS icon menu bar.

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Fill out the require INPUT and OUTPUT and note the selection of the function you wish to create. DO NOT CLICK ON OK

(5) Click on the VIEW button on the INDICES dialog box. This will display the "model" in the model maker window which will create the NDVI index image based upon the NDVI equation. You should see that the input and output properties have NOT been set your values. This is just a VIEW of how the model works. Explore the properties of the function. Then click on OK.

(6) When you view the results I like to use and Histogram Equalization as the contrast stretch (raster > contrast > histogram equalize)