### HELP ARTICLES

Help Articles are product support tips and information straight from the Harris Geospatial Technical Support team developed to help you use our products to their fullest potential.

### Radially averaged Fourier Spectrum -- 2d

6/6/1998

It is often necessary, when dealing with multidimensional data to compute the power spectrum as a function of |K|, the magnitude of the wavenumber vector. This is accomplished by computing the FFT and averaging power over circles of diameter |K|. Though fairly straightforward in theory, writing such a routine is often cumbersome because of... more »

### Optimizing derivative approximations in IDL

6/6/1998

Computing standard derivative approximations that are not included as part of the standard library (The discrete 2D Laplacian for example) can be very time consuming. This Help Article demonstrates how IDL's SHIFT function can be used, in place of a FOR loop, to improve performance when approximating derivatives. Use the SHIFT... more »

### Configuring Server-based FLEXnet/FLEXlm Licensing Through A Firewall

6/4/1998

THIS INFORMATION ONLY PERTAINS TO SOFTWARE VERSIONS IDL 8.5, ENVI 5.3 AND PRIOR Topic: How do I enable floating or server-based node-locked licensing through a firewall? Background Server-based Exelis Visual Information Solutions licenses (such as network floating licenses or server based node-locked licenses) require running the... more »

### Fitting a Surface to a Function of Two Independent Variables.

5/21/1998

This help article provides an example for fitting a surface to a function of two independent variables. This specific example fits a surface to the function: f(x,y) = -SIN(2.0 * x) + COS(0.5 * y) . but can be generalized to work with any function of two variables. Example: ;++++++++Begin: The Function to be Fit++++++++; Please Note: ... more »

### How does IDL release Virtual Memory?

5/21/1998

IDL does free its dynamic memory when it is done with it, and the IDL code has consistency checks that guard against memory leaks. You can use the IDL command:     HELP, /MEMORY to see how much memory IDL has allocated. However, just because IDL frees its memory does not mean that its virtual address space will shrink and... more »

## FEATURED HELP ARTICLE

### ENVI 5.4 / IDL 8.6 Quick Start Install and Licensing Guide

12/6/2016

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An ENVI quick reference booklet that provides users succinct steps on how to accomplish common tasks in ENVI.

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