【正文】 Select “”39。Select an ASCII file to read.39。,/MUST_EXIST) IDL RESTORE, file Once this is acplished, you can skip forward to the Data Analysis and Visualization section of this document. However, if you would like to learn how to input data into IDL it is highly remended that you continue working through this section. One of the easiest ways to open data into an IDL session is to use the import Macros built into the IDLDE that are used to input Binary, ASCII, and Image data. These Macros simply provide a shortcut to launch routines in IDL (. BINARY_TEMPLATE, READ_BINARY, ASCII_TEMPLATE, READ_ASCII, DIALOG_READ_IMAGE). There are also several routines in IDL built specifically to input files of the most mon formats (. JPEG, TIFF, HDF, etc.), and these all have a name that begins with IDL Short Course (version ) Research Systems, Inc. – A Kodak Company IDL? is a registered trademark of Research Systems, Inc. Page 11 of 37 “READ_*”. In addition, to read a file that is not one of the standard file formats supported by the READ_* routines, IDL provides a series of lowlevel routines that can be used to perform brute file I/O (. OPENR, POINT_LUN, READF, READU, ASSOC, etc.). Please consult the IDL documentation for further information on how to use these routines. Start by opening all of the data used in the exercises in the sections that follow. This data is stored in the IDL_Data/ folder included with this short course. There are 9 different types of data files that we are going to work with: ? “” : an ASCII text file containing 32bit floatingpoint simulated instrument response data in 2 columns (X an independent vector and Y a second order polynomial with random noise) ? “” : an ASCII text file containing a slightly more plex onedimensional dataset ? “” : an ASCII text file containing a uniform 10 x 10 twodimensional grid of random floatingpoint data ? “” : a Binary file with LSB byte order containing random, irregularlyspaced twodimensional data (. X, Y, Z) stored in a 3 column x 32 row floatingpoint array ? “” : a Binary file containing a 256 x 256 8bit grayscale CAT scan image ? “” : a 24bit TrueColor Joint Photographic Experts Group (JPEG) format image file of Maho Bay on Saint John in the . Virgin Islands ? Files found in the “Frames\” folder : a series of 450 x 450 8bit medical images of human anatomy taken at different viewing angles stored in DICOM format ? “” : a Binary file containing a 61 x 61 x 25 threedimensional byte array of volumetric pressure perturbations for a thunderstorm in units of millibars ? “” and “” : Binary files containing the vertices (3 x 1976 floatingpoint array) and polygon connectivity (15004 element longword vector) that define the polygonal mesh of a teapot To open all of these files into the current session of IDL and store them in named variables you can perform the following: To open the file “” we will use the Import ASCII macro. To launch this macro select Macros Import ASCII from the main IDLDE menu or hit the button on the IDLDE toolbar. A dialog will e up entitled “Select an ASCII file to read.”. Navigate to the IDL_Data\ folder, select the “” file, and hit Open. The macro will walk you through a series of 3 steps where you give IDL some information about the file so that it can determine how to import the data. By looking at the file “”, we know that 32bit floatingpoint data is aligned in 2 columns that are separated by six whitespace characters, and that have a label on the first line. Consequently, we will want to fillout the parameters in the Import ASCII macro as follows: IDL Short Course (version ) Research Systems, Inc. – A Kodak Company IDL? is a registered trademark of Research Systems, Inc. Page 12 of 37 Figure 3: Step 1 of 3 for the Import ASCII macro Figure 4: Step 2 of 3 for the Import ASCII macro IDL Short Course (version ) Research Systems, Inc. – A Kodak Company IDL? is a registered trademark of Research Systems, Inc. Page 13 of 37 Figure 5: Step 3 of 3 for the Import ASCII macro Once you hit Finish the macro will terminate and you will return to the main level of IDL. However, if you execute the HELP procedure you will notice that there is a new variable called X_Y_SIMPLE_ASCII defined: IDL help % At $MAIN$ X_Y_SIMPLE_ASCII STRUCT = Anonymous Array[1] The X_Y_SIMPLE_ASCII variable that was returned by the Import ASCII macro has taken a special form known as a structure. To see the contents of a structure you have to set the STRUCTURES keyword to the HELP procedure: IDL help, x_y_simple_ascii, /st ** Structure 1523a28, 2 tags, length=400, refs=1: X FLOAT Array[50] Y FLOAT Array[50] Notice that you can abbreviate keywords to the smallest string that still uniquely identifies the keyword for any given routine (. there are no other keywords to the HELP procedure that start with “st”). The floatingpoint data in the two columns that we defined as X and Y in the Import ASCII macro are currently stored in the two tags for this structure. To access the data within a structure you use the syntax “”. For example, to make the data easier to access you can pullout the X and Y data from the structure and store it in separate vector IDL Short Course (version ) Research Systems, Inc. – A Kodak Company IDL? is a registered trademark of Research Systems, Inc. Page 14 of 37 variables called xSimple and ySimple by executing the following statements: IDL xSimple = IDL ySimple = IDL help, xSimple, ySimple XSIMPLE FLOAT = Array[50] YSIMPLE FLOAT = Array[50] To delete the X_Y_SIMPLE_ASCII structure variable so it is not consuming memory wit