TeraScan has a number of non-display functions that are useful in the generation of hardcopy or digital export graphics products. Each of these functions can be run without writing graphics to the display screen, although a couple of functions (xinject, wedge, legend) require that the X windows server be running at the same time. The current collection of non-display graphics functions are listed below:
imscale scales input data to produced byte-valued image emath element-by-element variable arithmetic lookup applies lookup table to fixed point variables
coast creates an overlay with coastlines and boundaries etop creates a topographic overlay llgrid creates a latitude-longitude grid overlay
legend creates a multi-line text legend metafile wedge creates an annotated color wedge overlay metafile
llcontr2 creates contour overlay of 2-D gridded data llcontr creates contour overlay of 1-D random data orbit creates an overlay of a satellite track and swath post creates an overlay with point location and values vectors creates overlay metafile from vectors dataset
tovswind creates windbarb overlay file from TOVS data tracks creates overlay of DCS platform positions, tracks, values weather creates weather symbol overlay of Antarctic DCS data eggcv creates overlay of EG&G ARGOS platform data from DCS
xinject injects metafile overlays into image backgrounds
epsf exports 2-D dataset variables in encapsulated Postscript expbin exports TeraScan variable data in binary format
In TeraScan, graphics data is either image data or metafile overlay data. An image is any 2-D array of numeric data. A metafile is a sequence of graphics primitives defining an overlay to be applied to image data. In TeraScan, both metafiles and images are implemented as TeraScan dataset variables.
In virtually all cases, metafile variables are created one at a time; e.g., the coast function creates a dataset containing a single variable named coastline and no other variables. (That is why datasets containing a metafile variable are often also referred to as metafiles.) Functions such as assemble and copyvar can be used to store one or more metafile variables together with non-metafile variables in the same dataset.
Unlike metafile variables, image variables are often created in multiples; e.g., by extracting multiple sensor channels from a telemetry stream using an AVHRR or OLS ingestor.
Overlay metafiles are always created relative to a background, basically any image with earth location. Most often, metafiles are created relative to master files, trivial TeraScan datasets containing the description of a map projection and a null image background. (Master files are created using master, master2, master4.) Metafiles can only be overlaid on top of images parallel to the background upon which the metafiles are based. For example, a coastline created relative to a given master file can only be overlaid on top of images registered to that same master file.
TeraScan metafiles are discussed further in metafiles.
The following sequence shows how image data and metafile data are typically created and combined to produce a graphics product. Relevant functions are shown in parentheses.
Create static metafiles and retain them for repeated future use. (coast, llgrid, etop, wedge)
Create image data (2-D) by extracting sensor data from satellite telemetry and processing it into geophysically meaningful data.
Create non-image data (1-D) by extracting sensor data from satellite telemetry and processing it into geophysically meaningful data.
Create metafile overlay data derived from insitu data, image or non-image data. (llcontr, llcontr2, post, vectors, legend, tovswind, tracks, weather, eggcv).
Scale the image data to the appropriate values, most often byte data, but not necessarily. (imscale, emath, lookup).
Inject the metafile overlay data into the image data. (xinject).
Export the combined image and overlay data outside of TeraScan. (epsf, expbin).
Metafiles are referred to as static if they can be reused over more than one instance of image data. For example, a coastline and latitude/longitude grid can be reused over several images provided they are registered to the same master file that was used to create the coastline and grid.
Last Update: $Date: 1999/05/10 21:16:24 $