Description: This procedure reads OCTS (NASDA format) data files. Supported OCTS data file types are: Level-0, Level-1A, Level-1B, Level-2, Level-3 Mapped (no navigation yet) and Level_3 Binned Map. The data and associated information (such as navigation information, data units and raw-to-geophysical scaling information) are loaded into memory and made available for display. (See special notes on OCTS Level-0 display).
Note: There is no hard-coded limit to the number of files loaded into memory at one time. The only limit is the memory limit of your machine.
[Interactive
mode][Command mode]
Once an OCTS input file is selected, the widget expands to show all the available data products in that file. Once data products are selected, press the Load button to load the products into memory and make available for display. It is not necessary to close the OCTS Product Selection Widget in order to see the products in a new file, simply enter or select a new file and the product list will automatically update.
From Main Menu , select menu item Load -> OCTS (NASDA format).
File Selection Section:
| OCTS Filename | Files
can be selected in one of two ways:
|
| Select | Interactively select an OCTS input file. |
| Okay | Show a listing of the available data products in this file. (This is only needed if the user manually enters a file name and does not hit <RETURN>) |
| File Type | Displays information on what type of OCTS file has been selected (i.e., Level-0, Level-1B, Level-2, etc.). |
| Dimension | Displays information on the dimensions of a product in the selected input file. |
| Pixel range | Enter a range of pixels to read. |
| Line range | Enter a range of lines to read. |
| Pixel Sample Rate | Select a pixel sample rate for reading the data into memory. |
| Line Sample Rate | Select a line sample rate for reading the data into memory. |
| Load Palette | This option will be inactive if there is no color palette in the OCTS input file selected. If the option is active, then selecting it will read and load the color palette. Remember that any currently displayed images will be affected. |
Product Selection Section:
| Select One or Many Products buttons | Select any number of products desired for reading into memory. |
| Quit | Delete the Product Selection For OCTS widget. Products already loaded into memory will still be available. |
| Help | Show this help in HTML viewer. |
| Select All | Select all products listed. |
| Select None | Deselect all products listed. |
| Load | Read selected data products and attributes into memory, into available band list, and make available for display. |
Additional subsetting parameters for L3-Binned Mapped files: The following inputs allow the user to subset the L3-Binned Mapped data while loading it. Subsetting may be accomplished by either specifying the lat/lon range desired or the pixel/line range desired. Modifying pixel/line range values will cause the lat/lon range values to automatically recalculate and vice versa.
| Lat range (N/S) | The northern and southern latitude limits to be used for subsetting in the line dimension. |
| Line range | The line range to be used for subsetting. |
| Lon range (W/E) | The westernmost and easternmost longitude limits to be used for subsetting in the pixel dimension. |
| Pixel range | The pixel range to be used for subsetting. |
The OCTS Level-0 files are extremely large (about .5 Gigabytes/file). Understanding a little about the file organization and following a few rules of thumb will help you display Level-0 files as quickly as possible. In general, the time required to read a Level-0 file is directly proportional to the number of scan lines read. The total number of scan lines in the input file is the total number of image lines shown in the second Dimension value, divided by 10.
Level-0 file structure: Due to the Level-0 file structure, some data requests can be much slower than others. The files are organized by scan lines. Interleaved within each scan line are the data values for 12 bands across 10 detectors for 2222 pixels; the values for each detector are treated as separate image lines. In order to read a full band of data, therefore, it is necessary to read the entire file. Since each scan line contains 10 interleaved image lines, a subsample rate <=10 in the line dimension, will still require the entire file to be read. Therefore, your subsample rate in the line direction should be > 10 in order to save any time.
Example: Take an OCTS Level-0 file with dimensions 2222 pixels x 8360 image lines (836 scan lines). Subsampling by 20 in both dimensions will result in a small image 111x418 and will require reading 50% of the scan lines in the input file. By comparison, subscening this image full resolution (pixels 1 to 2222 and image lines 1 to 1000) will result in a large image 2222x1000 but will require reading only 11% of the input file. Therefore, although the resultant subsampled image is 50 times smaller than the resultant subscened image, it takes about 5 times longer to read.
Recommendations:
