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57-446: Modern systems typically use some sort of raster scan display to produce a map-like image. Early in radar development, however, numerous circumstances made such displays difficult to produce. People developed several different display types. Early radar displays used adapted oscilloscopes with various inputs. An oscilloscope generally receives three channels of varying (or oscillating) voltage as input and displays this information on

114-411: A cathode ray tube . The oscilloscope amplifies the input voltages and sends them into two deflection magnets and to the electron gun producing a spot on the screen. One magnet displaces the spot horizontally, the other vertically, and the input to the gun increases or decreases the brightness of the spot. A bias voltage source for each of the three channels allows the operator to set a zero point. In

171-469: A B-scope displaying range vs. elevation, rather than range vs. azimuth. They are identical in operation to the B-scope, the name simply indicating "elevation". E-scopes are typically used with height finding radars , which are similar to airborne radars but turned to scan vertically instead of horizontally, they are also sometimes referred to as "nodding radars" due to their antenna's motion. The display tube

228-406: A circular screen and scanned the beam from the center outwards. The deflection yoke rotated, causing the beam to rotate in a circular fashion. The screen often had two colors, often a bright short persistence color that only appeared as the beam scanned the display and a long persistence phosphor afterglow. When the beam strikes the phosphor, the phosphor brightly illuminates, and when the beam leaves,

285-469: A delay so it would appear slightly to the right of the other. The operator would then swing the antenna back and forth until both blips were the same height. This was sometimes known as a K-scope . A slightly modified version of the K-scope was commonly used for air-to-air (AI) and air-to-surface-vessel (ASV) radars. In these systems, the K-scope was turned 90 degrees so longer distances were further up

342-400: A focused electron beam . By association, it can also refer to a rectangular grid of pixels. The word rastrum is now used to refer to a device for drawing musical staff lines. The fundamental strategy underlying the raster data model is the tessellation of a plane, into a two-dimensional array of squares, each called a cell or pixel (from "picture element"). In digital photography ,

399-506: A further adaptation of the J-scope in the "spiral time base", which moved the blip both around the face and outward from the center. This produced a time base that was 7 feet (2.1 m) long, allowing very highly accurate measurements of range. To improve the accuracy of angle measurements, the concept of lobe switching became common in early radars. In this system, two antennas are used, pointed slightly left and right, or above and below,

456-522: A horizontal "slice" of the airspace on both sides of the aircraft out to the tracking angles of the radar. B-scope displays were common in airborne radars in the 1950s and 60s, which were mechanically scanned from side to side, and sometimes up and down as well. The spot was swept up the Y-axis in a fashion similar to the A-scope's X-axis, with distances "up" the display indicating greater range. This signal

513-431: A pair of antennas arranged at right angles. Using a device known as a radiogoniometer , the operator could determine the bearing of the target, and by combining their range measurement with the bearing, they could determine a target's location in space. The system also had a second set of antennas, displaced vertically along the receiver towers. By selecting a pair of these antennas at different heights and connecting them to

570-425: A printer setting of 1200 DPI. Raster-based image editors, such as PaintShop Pro , Corel Painter , Adobe Photoshop , Paint.NET , Microsoft Paint , Krita , and GIMP , revolve around editing pixels , unlike vector-based image editors, such as Xfig , CorelDRAW , Adobe Illustrator , or Inkscape , which revolve around editing lines and shapes ( vectors ). When an image is rendered in a raster-based image editor,

627-408: A radar display, the output signal from the radar receiver is fed into one of three input channels in the oscilloscope. Early displays generally sent this information to either X channel or Y channel to displace the spot on the screen to indicate a return. More modern radars typically used a rotating or otherwise moving antenna to cover a greater area of the sky, and in these cases, electronics, slaved to

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684-423: A raster approach. Each on-screen pixel directly corresponds to a small number of bits in memory. The screen is refreshed simply by scanning through pixels and coloring them according to each set of bits. The refresh procedure, being speed critical, is often implemented by dedicated circuitry, often as a part of a graphics processing unit . Using this approach, the computer contains an area of memory that holds all

741-399: A very different meaning, and this can be misleading. Because, through the dithering process, the printer builds a single image pixel out of several printer dots to increase color depth , the printer's DPI setting must be set far higher than the desired PPI to ensure sufficient color depth without sacrificing image resolution. Thus, for instance, printing an image at 250 PPI may actually require

798-402: Is based on a (usually rectangular, square-based) tessellation of the 2D plane into cells, each containing a single value. To store the data in a file, the two-dimensional array must be serialized. The most common way to do this is a row-major format, in which the cells along the first (usually top) row are listed left to right, followed immediately by those of the second row, and so on. In

855-415: Is displayed by drawing a second "blip" offset from the target indicator by a short distance, the slope of the line between the two blips indicates the elevation relative to the radar. For instance, if the blip were displaced directly to the right this would indicate that the target is at the same elevation as the radar. The offset is created by dividing the radio signal into two, then slightly delaying one of

912-460: Is lost, although certain vectorization operations can recreate salient information, as in the case of optical character recognition . Early mechanical televisions developed in the 1920s employed rasterization principles. Electronic television based on cathode-ray tube displays are raster scanned with horizontal rasters painted left to right, and the raster lines painted top to bottom. Modern flat-panel displays such as LED monitors still use

969-530: Is the G-scope , which overlays a graphical representation of the range to the target. This is typically represented by a horizontal line that "grows" out from the target indicator blip to form a wing-like shape. The wings grew in length at shorter distances to indicate the target was closer, as does the aircraft's wings when seen visually. A "shoot now" range indicator is often supplied as well, typically consisting of two short vertical lines centered on either side of

1026-424: Is then stored for each pixel. For most images, this value is a visible color, but other measurements are possible, even numeric codes for qualitative categories. Each raster grid has a specified pixel format , the data type for each number. Common pixel formats are binary , gray-scale , palettized , and full-color , where color depth determines the fidelity of the colors represented, and color space determines

1083-512: Is vector, rendering specifications and software such as PostScript are used to create the raster image. Three-dimensional voxel raster graphics are employed in video games and are also used in medical imaging such as MRI scanners . Geographic phenomena are commonly represented in a raster format in GIS . The raster grid is georeferenced , so that each pixel (commonly called a cell in GIS because

1140-666: The Exif standard. High-resolution raster grids contain a large number of pixels, and thus consume a large amount of memory. This has led to multiple approaches to compressing the data volume into smaller files. The most common strategy is to look for patterns or trends in the pixel values, then store a parameterized form of the pattern instead of the original data. Common raster compression algorithms include run-length encoding (RLE), JPEG , LZ (the basis for PNG and ZIP ), Lempel–Ziv–Welch (LZW) (the basis for GIF ), and others. For example, Run length encoding looks for repeated values in

1197-481: The pulse repetition frequency of the radar. This spread out the blips across the display according to the time they were received. Since the return time of the signal corresponds to twice the distance to the target divided by the speed of light , the distance along the axis directly indicates the range to any target. This was usually measured against a scale above the display. Chain Home signals were normally received on

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1254-614: The visible spectrum ; the large CCD bitmapped sensor at the Vera C. Rubin Observatory captures 3.2 gigapixels in a single image (6.4 GB raw), over six color channels which exceed the spectral range of human color vision. Most computer images are stored in raster graphics formats or compressed variations, including GIF , JPEG , and PNG , which are popular on the World Wide Web . A raster data structure

1311-446: The "picture" part of "pixel" is not relevant) represents a square region of geographic space. The value of each cell then represents some measurable ( qualitative or quantitative ) property of that region, typically conceptualized as a field . Examples of fields commonly represented in rasters include: temperature, population density, soil moisture, land cover, surface elevation, etc. Two sampling models are used to derive cell values from

1368-508: The 1990s. PPI displays are actually quite similar to A-scopes in operation, and appeared fairly quickly after the introduction of radar. As with most 2D radar displays, the output of the radio receiver was attached to the intensity channel to produce a bright dot indicating returns. In the A-scope a sawtooth voltage generator attached to the X-axis moves the spot across the screen, whereas in the PPI

1425-426: The A-scope was the amplified return signal received from the radar, which was sent into the Y-axis of the display. Returns caused the spot to be deflected downward (or upward on some models), drawing vertical lines on the tube. These lines were known as a "blip" (or "pip"). The X-axis input was connected to a sawtooth voltage generator known as a time base generator that swept the spot across the display, timed to match

1482-406: The aircraft starting to the left of the approach line and then being guided toward it. Raster graphics In computer graphics and digital photography , a raster graphic represents a two-dimensional picture as a rectangular matrix or grid of pixels , viewable via a computer display , paper , or other display medium. A raster image is technically characterized by the width and height of

1539-503: The array, and replaces them with the value and the number of times it appears. Thus, the raster above would be represented as: This technique is very efficient when there are large areas of identical values, such as a line drawing, but in a photograph where pixels are usually slightly different from their neighbors, the RLE file would be up to twice the size of the original. Some compression algorithms, such as RLE and LZW, are lossless , where

1596-409: The boresight of the system. The received signal would differ in strength depending on which of the two antennas was more closely pointed at the target, and be equal when the antenna was properly aligned. To display this, both antennas were connected to a mechanical switch that rapidly switched between the two, producing two blips in the display. In order to differentiate them, one of the two receivers had

1653-472: The data that are to be displayed. The central processor writes data into this region of memory and the video controller collects them from there. The bits of data stored in this block of memory are related to the eventual pattern of pixels that will be used to construct an image on the display. An early scanned display with raster computer graphics was invented in the late 1960s by A. Michael Noll at Bell Labs , but its patent application filed February 5, 1970,

1710-412: The dimmer long persistence afterglow would remain lit where the beam struck the phosphor, alongside the radar targets that were "written" by the beam, until the beam re-struck the phosphor. The specialist Beta Scan Scope was used for precision approach radar systems. It displays two lines on the same display, the upper one (typically) displaying the vertical approach (the glideslope ), and the lower one

1767-478: The example at right, the cells of tessellation A are overlaid on the point pattern B resulting in an array C of quadrant counts representing the number of points in each cell. For purposes of visualization a lookup table has been used to color each of the cells in an image D. Here are the numbers as a serial row-major array: 1 3 0 0 1 12 8 0 1 4 3 3 0 2 0 2 1 7 4 1 5 4 2 2 0 3 1 2 2 2 2 3 0 5 1 9 3 3 3 4 5 0 8 0 2 4 3 2 8 4 3 2 2 7 2 3 2 10 1 5 2 1 3 7 To reconstruct

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1824-407: The field: in a lattice , the value is measured at the center point of each cell; in a grid , the value is a summary (usually a mean or mode) of the value over the entire cell. Raster graphics are resolution dependent, meaning they cannot scale up to an arbitrary resolution without loss of apparent quality . This property contrasts with the capabilities of vector graphics , which easily scale up to

1881-401: The horizontal approach. A marker indicates the desired touchdown point on the runway, and often the lines are angled towards the middle of the screen to indicate this location. A single aircraft's "blip" is also displayed, superimposed over both lines, the signals being generated from separate antennas. Deviation from the centerline of the approach can be seen and easily relayed to the pilot. In

1938-428: The image in pixels and by the number of bits per pixel . Raster images are stored in image files with varying dissemination , production , generation , and acquisition formats . The printing and prepress industries know raster graphics as contones (from continuous tones ). In contrast, line art is usually implemented as vector graphics in digital systems. Many raster manipulations map directly onto

1995-597: The image is composed of millions of pixels. At its core, a raster image editor works by manipulating each individual pixel. Most pixel-based image editors work using the RGB color model , but some also allow the use of other color models such as the CMYK color model . Aircraft interception radar Too Many Requests If you report this error to the Wikimedia System Administrators, please include

2052-414: The image, the upper portion of the display shows the vertical situation, and the lower portion the horizontal. In the vertical, the two diagonal lines show the desired glideslope (upper) and minimum altitude approach (lower). The aircraft began its approach below the glideslope and captured it just before landing. The proper landing point is shown by the horizontal line at the left end. The lower display shows

2109-439: The linear distance along it. This arrangement allows greater accuracy in reading the range with the same sized display as an A-scope because the trace uses the full circumference rather than just the horizontal distance (so the time base is π times longer. For instance, on a typical . An electro-mechanical version of the J-scope display remained common on consumer boating depth meters until the 1990s. W. A. S. Butement developed

2166-453: The mathematical formalisms of linear algebra , where mathematical objects of matrix structure are of central concern. The word "raster" has its origins in the Latin rastrum (a rake), which is derived from radere (to scrape). It originates from the raster scan of cathode-ray tube (CRT) video monitors , which draw the image line by line by magnetically or electrostatically steering

2223-509: The mechanical motion of the antenna, typically moved the X and Y channels, with the radar signal being fed into the brightness channel. The original radar display, the A-scope or A-display , shows only the range, not the direction, to targets. These are sometimes referred to as R-scopes for range scope . A-scopes were used on the earliest radar systems during World War II , notably the seminal Chain Home (CH) system. The primary input to

2280-415: The middle of the display. To make an interception, the pilot guides his aircraft until the blip is centered, then approaches until the "wings" fill the area between the range markers. This display recreated a system commonly used on gunsights , where the pilot would dial in a target's wingspan and then fire when the wings filled the area inside a circle in their sight. This system allowed the pilot to estimate

2337-496: The most appropriate image resolution for a given printer-resolution can pose difficulties, since printed output may have a greater level of detail than a viewer can discern on a monitor. Typically, a resolution of 150 to 300 PPI works well for 4-color process ( CMYK ) printing. However, for printing technologies that perform color mixing through dithering ( halftone ) rather than through overprinting (virtually all home/office inkjet and laser printers), printer DPI and image PPI have

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2394-425: The naming was not universal. Size of A-scope displays vary, but 5 to 7 inch diagonal was often used on a radar display. The 7JPx series of CRTs (7JP1, 7JP4 and 7JP7) was originally designed as an A-scope display CRT. A B-scope or b-scan provides a 2-D "top down" representation of space, with the vertical axis typically representing range and the horizontal axis azimuth (angle). The B-scope's display represented

2451-474: The original pixel values can be perfectly regenerated from the compressed data. Other algorithms, such as JPEG, are lossy , because the parameterized patterns are only an approximation of the original pixel values, so the latter can only be estimated from the compressed data. Vector images (line work) can be rasterized (converted into pixels), and raster images vectorized (raster images converted into vector graphics), by software. In both cases some information

2508-407: The output of two such generators is used to rotate the line around the screen. Some early systems were mechanical, using a rotating deflection coil around the neck of the display tube, but the electronics needed to do this using a pair of stationary deflection coils were not particularly complex, and were in use in the early 1940s. Radar cathode ray tubes such as the 7JP4 used for PPI displays had

2565-455: The plane is the visual field as projected onto the image sensor ; in computer art , the plane is a virtual canvas; in geographic information systems , the plane is a projection of the Earth's surface. The size of each square pixel, known as the resolution or support , is constant across the grid. Raster or gridded data may be the result of a gridding procedure. A single numeric value

2622-409: The quality of the device rendering them. Raster graphics deal more practically than vector graphics with photographs and photo-realistic images, while vector graphics often serve better for typesetting or for graphic design . Modern computer-monitors typically display about 72 to 130 pixels per inch (PPI), and some modern consumer printers can resolve 2400 dots per inch (DPI) or more; determining

2679-469: The radiogoniometer, they could determine the vertical angle of the target, and thus estimate its altitude. Since the system could measure both range and altitude, it was sometimes known as an HR-scope , from "height-range". Early American , Dutch and German radars used the J-scope , which resembled a circular version of the A-scope. These display range as an angle around the display face, as opposed to

2736-399: The range of color coverage (which is often less than the full range of human color vision ). Most modern color raster formats represent color using 24 bits (over 16 million distinct colors), with 8 bits (values 0–255) for each color channel (red, green, and blue). The digital sensors used for remote sensing and astronomy are often able to detect and store wavelengths beyond

2793-402: The range to the target. In this case, however, the range is being measured directly by the radar, and the display was mimicking the optical system to retain commonality between the two systems. The PPI display provides a 2-D "all round" display of the airspace around a radar site. The distance out from the center of the display indicates range, and the angle around the display is the azimuth to

2850-486: The scope instead of further to the right. The output of one of the two antennas was sent through an inverter instead of a delay. The result was that the two blips were displaced on either side of the vertical baseline, both at the same indicated range. This allowed the operator to instantly see which direction to turn; if the blip on the right was shorter, they needed to turn to the right. These types of displays were sometimes referred to as ASV-scopes or L-scopes , although

2907-440: The signals so it appears offset on the display. The angle was adjusted by delaying the time of the signal via a delay, the length of the delay being controlled by a voltage varying with the vertical position of the antenna. This sort of elevation display could be added to almost any of the other displays, and was often referred to as a "double dot" display. A C-scope displays a "bullseye" view of azimuth vs. elevation. The "blip"

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2964-419: The target. The current position of the radar antenna is typically indicated by a line extending from the center to the outside of the display, which rotates along with the antenna in realtime. It is essentially a B-scope extended to 360 degrees. The PPI display is typically what people think of as a radar display in general, and was widely used in air traffic control until the introduction of raster displays in

3021-423: The two-dimensional grid, the file must include a header section at the beginning that contains at least the number of columns, and the pixel datatype (especially the number of bits or bytes per value) so the reader knows where each value ends to start reading the next one. Headers may also include the number of rows, georeferencing parameters for geographic data, or other metadata tags, such as those specified in

3078-469: Was abandoned at the Supreme Court in 1977 over the issue of the patentability of computer software. During the 1970s and 1980s, pen plotters , using Vector graphics , were common for creating precise drawings, especially on large format paper. However, since then almost all printers create the printed image as a raster grid, including both laser and inkjet printers. When the source information

3135-512: Was displayed indicating the direction of the target off the centreline axis of the radar, or more commonly, the aircraft or gun it was attached to. They were also known as "moving spot indicators" or "flying spot indicators" in the UK, the moving spot being the target blip. Range is typically displayed separately in these cases, often using a second display as an L-scope. Almost identical to the C-scope

3192-447: Was generally rotated 90 degrees to put the elevation axis vertical in order to provide a more obvious correlation between the display and the "real world". These displays are also referred to as a Range-Height Indicator , or RHI , but were also commonly referred to (confusingly) as a B-scope as well. The H-scope is another modification of the B-scope concept, but displays elevation as well as azimuth and range. The elevation information

3249-408: Was mixed with a varying voltage being generated by a mechanical device that depended on the current horizontal angle of the antenna. The result was essentially an A-scope whose range line axis rotated back and forth about a zero point at the bottom of the display. The radio signal was sent into the intensity channel, producing a bright spot on the display indicating returns. An E-scope is essentially

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