Previous post discussed how to use WINDOW function to crop big satellite image, but it only implements for rectangular area. Distance function in IDRISI that used for creating a driver of land-use growth (previous post about driver creation) also in rectangular extent. This post tries to explain how to create a driver with the true extent region, e.g. Bekasi city.

The dark area was a true extent of Bekasi city. The problem is how to crop the image based on Bekasi city? I have searched IDRISI function for cropping an area similar with “crop” function in ArcGIS but I have not found it yet. Finally I found the Mathematical function in “GIS analysis” menu. To use this function we have to prepare the crop image first. (Please write a comment for other method suggestion).

The background and the study area are separated with zero and one classes respectively. Since multiplying a zero and one to a driver will create a zero and an existing value of the driver, the background will be zero and the actual driver only presents with true extent of Bekasi city.

Input the first, second, and output image for overlaying calculation. Choose first * second for multiplying first with the second image. It seems easy, but in the implementation users must consider many things, e.g. the projection and extent between first and second images. Use “Metadata” to match both images.

Use “PROJECT” to match first with second images (See previous post how to use this function).