Moscow 2011
To change the background of a sheet in AutoCad:
Service
setting
Screen
Colors
accept > ok
Selecting objects
Show some lines
Selection of objects is possible either one by one or by means of a rectangular area, and if you place the cursor on the left and above the drawing, then for selection it is necessary that the objects fall completely into the area. If we select from the bottom right (that is, from the lower right corner), then it is enough to capture only some parts of the selected objects, and they will be selected completely.
2. To cancel the action, press the right mouse button, and in the drop-down window, select the command "deselect"
Zooming - zooming in and out of the drawing
You can use the magnifying glass icon to narrate. Click on this icon and when the icon (magnifying glass + -) appears, then moving the mouse, while holding the left button, will move the drawing away from you, and moving towards yourself will bring the drawing closer.
We select the icon from the drop-down list, select the object that we want to zoom in on and press the spacebar.
If you select the last icon “Show to borders” in the drop-down list, then the elements of the drawing will be displayed on the screen.
III. The way to enlarge an image is to quickly double-click on the mouse wheel.
And the third icon "show previous" by pressing this button, we return the previous zoom.
Panning is moving around the drawing (also possible in 2 ways) either by pressing the foot and holding the right mouse button, or by holding the mouse wheel.
Absolute and relative coordinate system.
Entering the coordinates (20,20) implies an indent along axesX by 20mm. And by axesYby 20mm., relative to absolute zero.
Entering then the coordinates (50,50), we get, the coordinates of the 2nd point are still relative to the origin of the coordinate (that is, absolute zero).
However, sometimes it becomes necessary to enter coordinates relative to an arbitrary point. To do this, call the "segment" command and set the beginning of the segment at any point on the screen (in order for the prompts to be visible, it is necessary that the dynamic input be active) and then the indicated coordinates will be given relative to an arbitrarily chosen origin.
In order to make sure of this, we enter the menu "Dimensions" and "Linear dimension"
And having set these dimensions, we notice that along the “Y” axis - 50mm, Esc, (space) and along the “x” axis -50mm.
To build a square with a side of 10mm, we introduce an arbitrary point and set the coordinates of the points.
Origin (-10;0) – lower left point,
(0; -10) – bottom right point.
(10; 0) – upper right point,
(0;10) – upper left point.
The origin of coordinates occurs counterclockwise, sequentially.
Construct the following figure using the coordinate system.
| X | Y |
| 60 - lower horizontal straight | 0 - lower horizontal line |
| 20 |
|
| 120 - the intersection of the lower (rhombus) | |
| -60 | 0 |
| 40 - right and left line of the rectangle (vertical) |
|
| 30- left upper line | |
| 20 - right upper line |
|
Polar relative coordinate system
In the case when we want to set the length of the segment and the angle (alpha) to the horizontal, you must first set an arbitrary point (or the coordinates of a given point relative to absolute zero), after which we enter the length of the segment before, 60mm, and then, by successively pressing the Shift + keys
To display the size horizontally or vertically, use the "Dimensions" menu ͢
"Linear Dimension"
To display absolute length
Use the menu "Dimensions" > Parallel Dimension "
Toolbars
AutoCad workspace starts from main menu
On the side of the worksheet, there may be toolbars that display not the full range of main menu commands, but the most frequently used commands.
You can add or remove toolbars from the workspace, in order to add any toolbar, right-click on any of the icons of the top toolbar and check the box next to the name of the menu whose toolbar we would like to display.
The very first top toolbar is called "STANDARD"
The transition from tape to classic AutoCad is done through the Workspace toolbar
Saving a profile is done through the command "service" > "configure" > (scroll arrows to the end) > "profiles" > "add" > "Name"; and if you want to insert "description" > OK
Drawing 2D shapes (Ray, line, segment)
Drawing such primitives as a line, a ray and a segment is carried out using the "Drawing" menu or the drawing panel with the icons "straight", "ray", "segment".
In order to draw a straight line in AutoCad, you need to click on the drawing icons
The starting point can be set either arbitrarily or by specifying coordinates (x; y). Note that the straight line rotates freely relative to the given point, in order to fix the straight line, you must specify either the coordinates of the 2nd point, or the length of the segment and the angle (shift +
To draw a beam, you must use the "draw" menu, because. there is no such icon in the drawing panel.
By clicking in an arbitrary place on the screen, we pay attention to the fact that the beam also rotates freely relative to the starting point.
We set the coordinates of the second point and fix a ray of a certain length. To exit drawing mode, press Esc, space, or Enter. And the segment, which is built on two points, is also called at the beginning of the “segment” tools.
AutoCad offers us the drawing of several segments to the given coordinates of the second point, taking the end of the already drawn segment as the first point,
If any prompts pop up while moving around the screen, this function can be excluded by pressing the "BS" - Quick Properties button
Circle and arc
In the Draw panel, a circle is represented by an icon, an arc. However, we will use the "Drawing" menu from the drop-down list, select the "Circle" command - and by clicking on the arrow, we notice several ways to set a circle:
Center and radius
Center and Diameter
2 points
3 points
2 touch points, radius
3 touch points
When choosing the "circle" icon, we are prompted to select a default radius, if you need to select a diameter, you need to right-click and select the diameter command, then enter the linear size of the diameter from the keyboard.
If we choose to draw a circle using three points or two points, then by clicking on the “circle” icon, right-click and select 3t or 2t from the list.
The method is the construction of a circle by two touch points and a radius.
This way of constructing a circle provides for the presence of two more segments, which the constructed circle should touch.
Therefore, first we build 2 segments, after which we enter the "Drawing" menu and select the "KKR" command, the tooltip requires "Specify a point on the object that sets the first tangent" - move the cursor over the first segment and click the left mouse button in an arbitrary point lying on the segment, we do the same when choosing the second point of contact, only this time we select on the second segment.
The radius of the circle can be accepted by default or set independently by means of entering its value from the keyboard.
The method is the construction of a circle along 3 tangents. This method is used if it is necessary to inscribe a triangle in a circle.
In this case, first we build a triangle from segments, then we enter the “drawing” menu, select the “three touch points” command and select all three segments one by one.
If we draw a closed contour from segments, then we can use the context menu command (right-click) "close".
Arc.
For the image of an arc (part of a circle), we will also use the menu "drawing"\u003e "Arc"
Let's consider how to draw an arc through the task "center, start, end" in the tooltip, you need to specify the center of the arc, which can be entered from the keyboard in the form of a point coordinate (X; Y). Then we enter the coordinates of the beginning of the arc (remember that the arc is always drawn counterclockwise) and enter the coordinates of the end of the arc.
2 ways to draw an arc, center start corner.
In the tooltip, you need to enter the center of the arc, which can be set either by arbitrary clicking at any point in the workspace or by entering the coordinates of the point (20;20), then enter the coordinates of the starting point of the arc (X;Y) and then the angle of rotation, taking into account drawing the arc against clockwise (45 degrees; 90 degrees - 270 degrees).
And the last way is to set the arc through "center, start, length"
In an arbitrary place, we indicate the center and the beginning of the arc. Under the long arc should be understood the length of the chord.
No less often use the command in the menu "Draw"\u003e Arc\u003e "Continue"
In order to use the continue command, you must first draw that primitive whose last point will be the beginning of the arc.
The path will be a segment, having drawn it, we enter the drawing menu “Drawing” > “Arc” > “Continue”.
We notice that the depicted arc is tied to the end of the segment, i.e. to its end point, then, depending on our task, it is possible to extend the arc in any direction and up to any length.
This command is most often used when joining two segments.
contour and area.
The "area" icon is located in the drawing panel, while the outline icon is called only from the "Drawing" menu. The "area" command is used to add or subtract primitives when, having several simple primitives, it is necessary to create a more complex figure. Let's draw a rectangle and a circle on the working space, so that the radius of the circle would be equal to the side of the rectangle.
E 
If we need to get a figure depicted on the workspace, then this is possible by adding a circle and a rectangle.
However, by its type, the circle is around, and the rectangle is polyline , as we know, only homogeneous quantities can be subtracted and added. To make the type of both primitives the same, use the "area" command, after clicking on the "area" icon, select all those objects with which we will add or subtract in the future.
To solve most problems in applied sciences, it is necessary to know the location of an object or point, which is determined using one of the accepted coordinate systems. In addition, there are elevation systems that also determine the altitude location of a point on
What are coordinates
Coordinates are numeric or literal values that can be used to determine the location of a point on the terrain. As a consequence, a coordinate system is a set of values of the same type that have the same principle for finding a point or object.
Finding the location of a point is required to solve many practical problems. In a science such as geodesy, determining the location of a point in a given space is the main goal, on the achievement of which all subsequent work is based.
Most coordinate systems, as a rule, define the location of a point on a plane limited by only two axes. In order to determine the position of a point in three-dimensional space, a system of heights is also used. With its help, you can find out the exact location of the desired object.
Briefly about coordinate systems used in geodesy
Coordinate systems determine the location of a point on a territory by giving it three values. The principles of their calculation are different for each coordinate system.
The main spatial coordinate systems used in geodesy:
- Geodetic.
- Geographic.
- Polar.
- Rectangular.
- Zonal Gauss-Kruger coordinates.
All systems have their own starting point, values for the location of the object and scope.
Geodetic coordinates
The main figure used to read geodetic coordinates is the earth's ellipsoid.
An ellipsoid is a three-dimensional compressed figure that best represents the figure of the globe. Due to the fact that the globe is a mathematically incorrect figure, it is the ellipsoid that is used instead to determine geodetic coordinates. This facilitates the implementation of many calculations to determine the position of the body on the surface.
Geodetic coordinates are defined by three values: geodetic latitude, longitude, and altitude.
- Geodetic latitude is an angle whose beginning lies on the plane of the equator, and the end lies at the perpendicular drawn to the desired point.
- Geodetic longitude is the angle that is measured from the zero meridian to the meridian on which the desired point is located.
- Geodetic height - the value of the normal drawn to the surface of the ellipsoid of the Earth's rotation from a given point.
Geographical coordinates
To solve high-precision problems of higher geodesy, it is necessary to distinguish between geodetic and geographical coordinates. In the system used in engineering geodesy, such differences, due to the small space covered by the work, as a rule, do not.
An ellipsoid is used as a reference plane to determine geodetic coordinates, and a geoid is used to determine geographical coordinates. The geoid is a mathematically incorrect figure, closer to the actual figure of the Earth. For its leveled surface, they take that which is continued under sea level in its calm state.
The geographic coordinate system used in geodesy describes the position of a point in space with three values. longitude coincides with the geodesic, since the reference point will also be called Greenwich. It passes through the observatory of the same name in the city of London. determined from the equator drawn on the surface of the geoid.
Height in the local coordinate system used in geodesy is measured from sea level in its calm state. On the territory of Russia and the countries of the former Union, the mark from which the heights are determined is the Kronstadt footstock. It is located at the level of the Baltic Sea.
Polar coordinates
The polar coordinate system used in geodesy has other nuances of the product of measurements. It is used in small areas of terrain to determine the relative location of a point. The reference point can be any object marked as a source. Thus, using polar coordinates, it is impossible to determine the unambiguous location of a point on the territory of the globe.
Polar coordinates are defined by two quantities: angle and distance. The angle is measured from the north direction of the meridian to a given point, determining its position in space. But one angle will not be enough, so a radius vector is introduced - the distance from the standing point to the desired object. With these two options, you can determine the location of the point in the local system.
As a rule, this coordinate system is used for engineering work carried out on a small area of area.
Rectangular coordinates
The rectangular coordinate system used in geodesy is also used in small areas of the terrain. The main element of the system is the coordinate axis from which the reference is made. The coordinates of a point are found as the length of perpendiculars drawn from the abscissa and ordinate axes to the desired point.
The north direction of the x-axis and the east of the y-axis are considered positive, and the south and west are negative. Depending on the signs and quarters, the location of a point in space is determined.
Gauss-Kruger coordinates
The Gauss-Kruger coordinate zonal system is similar to the rectangular one. The difference is that it can be applied to the entire territory of the globe, and not just to small areas.
The rectangular coordinates of the Gauss-Kruger zones, in fact, are the projection of the globe onto a plane. It arose for practical purposes to depict large areas of the Earth on paper. Transferring distortions are considered insignificant.
According to this system, the globe is divided by longitude into six-degree zones with the axial meridian in the middle. The equator is in the center along a horizontal line. As a result, there are 60 such zones.
Each of the sixty zones has its own system of rectangular coordinates, measured along the ordinate axis from X, and along the abscissa - from the area of the earth's equator Y. To unambiguously determine the location on the territory of the entire globe, the zone number is put in front of the X and Y values.
The values of the x-axis in Russia are usually positive, while the values of y can be negative. In order to avoid the minus sign in the values of the abscissa axis, the axial meridian of each zone is conditionally moved 500 meters to the west. Then all coordinates become positive.
The coordinate system was proposed by Gauss as possible and calculated mathematically by Krüger in the middle of the twentieth century. Since then, it has been used in geodesy as one of the main ones.
Height system
The systems of coordinates and heights used in geodesy are used to accurately determine the position of a point on the Earth. Absolute heights are measured from sea level or other surface taken as the original. In addition, there are relative heights. The latter are counted as an excess from the desired point to any other. It is convenient to use them for working in the local coordinate system in order to simplify the subsequent processing of the results.
Application of coordinate systems in geodesy
In addition to the above, there are other coordinate systems used in geodesy. Each of them has its own advantages and disadvantages. There are also their own areas of work for which this or that method of determining the location is relevant.
It is the purpose of the work that determines which coordinate systems used in geodesy are best used. For work in small areas, it is convenient to use rectangular and polar coordinate systems, and for solving large-scale problems, systems are needed that allow covering the entire territory of the earth's surface.
Performing a flight along a given airway or route in order to bring the aircraft to a given point or landing aerodrome requires the crew to know the current position relative to the earth's surface. This requirement follows from the fact that the turning points of the flight route and the landing airfield are usually specified by geographical points, for example, the names of settlements or their geographical coordinates, which allow you to plot a given track on a flight map or enter them into the programming device of the navigation complex.
Knowing the current position of the aircraft corresponding to a given moment in time, the crew can determine the correctness of the flight: whether the actual track coincides with the given one. Correction of possible deviations is achieved by introducing amendments to the flight mode, i.e., by correcting the course and airspeed of the flight.
The aircraft position can be obtained directly and indirectly. The direct determination of the MS is carried out by fixing the moment of the flight of the aircraft over the identified landmark and with the help of technical means of aircraft navigation. In the first case, as a rule, the moment when the aircraft is strictly above some reference point (object) is visually noted. This is the most reliable way to determine MS. However, here it is extremely important to reliably identify the landmark, since an error can lead to a loss of orientation.
The direct determination of the MS with the help of technical means of aircraft navigation is achieved by fixing the moment of flight over a radar landmark or a radio beacon. Indirect determination of the MS is carried out by measuring some parameters, for example, azimuth, range, height of the celestial body, etc., which are functionally dependent on the relative position of the aircraft and the external "source of navigation information. As a result of the measurement, the coordinates of the MS are obtained corresponding to the moment of determination, but more often all in a coordinate system different from the one in which the track is controlled (dead reckoning).They require further transformation.As sources of positional information, ground radio beacons, visual and radar landmarks, celestial bodies of natural and artificial origin are used.
The MC coordinates obtained on the basis of external information are called absolute, since they do not depend on the navigation and flight modes of flight, the range and duration of the flight until the MC is determined. The accuracy of absolute coordinates is determined only by the means and conditions of measurement, as well as by the relative position of the aircraft and the source of positional information.
Currently, the following methods for determining absolute coordinates are used: by the moment of passage of a reference point; review and comparative; coordinate transformations. Each of them has its advantages and disadvantages, determined by the features of the method itself and its technical implementation.
Continuous control of the path in the process of aircraft navigation is possible by two methods: by determining the absolute coordinates or by calculating the distance traveled.
The first method can be implemented if it is possible to continuously obtain positional information from an external source. This can be achieved by using long-range radio navigation systems and satellite navigation systems that cover the entire intended flight area with their working areas.
However, in most cases, the measured absolute coordinates are used discretely, that is, at certain intervals. Therefore, for continuous navigation, the second method is implemented, which uses relative coordinates counted from the last MS obtained as a result of external information processing. Relative coordinates are determined by dead reckoning based on the integration of the ground velocity vector or aircraft accelerations over time. Consequently, this makes it possible to obtain not the MS coordinates themselves, but only their increment in time.
Dead reckoning allows you to determine the coordinates of the MS relative to the previously defined absolute ones. Thus, as a result of the dead reckoning, the coordinates of the current MS are, as it were, “preserved” in time and space between the moments when the absolute coordinates are determined.
The main disadvantage of dead reckoning is that as soon as the number system is violated, for example, in the event of a power failure of the navigation complex, it is no longer possible to restore the current coordinates of the MS. To do this, you need to determine the absolute coordinates.
Dead reckoning uses additional information about heading, aircraft speed and wind. The process of integration (summation) of the ground velocity vector leads to the appearance of an increasing numeration error. Therefore, the accuracy of aircraft navigation largely depends on the duration of the flight in an autonomous mode, during which the MC was not specified and its absolute coordinates were not determined. This shows the connection and difference between relative and absolute coordinates. In principle, for reliable navigation, absolute coordinates contain enough navigational information, while the information contained in relative coordinates is quickly lost due to increasing reckoning errors.
Programming in absolute coordinates - G90. Programming in relative coordinates - G91. The G90 instruction will interpret the movements as absolute values with respect to the active zero point. The G91 instruction will interpret the moves as increments from previously reached positions. These instructions are modal.
Setting coordinate values - G92. The G92 instruction can be used in a block without axis (coordinate) information or with axis coordinate information. In the absence of axial information, all coordinate values are converted to the machine coordinate system; in this case, all compensations (corrections) and zero offset are removed. If axial information is available, the specified coordinate values become current. This instruction does not initiate any movements, it operates within one block.
N…G92 X0 Y0 /The current X and Y coordinates are set to zero. The current value of the Z coordinate remains unchanged.
N…G92 /Offsets and zero offsets are removed.
Plane selection - G17 (XY plane), G18 (XZ plane), G19 (YZ plane). The instructions define the choice of the work plane in the workpiece or program coordinate system. Operation of G02, G03, G05 instructions, polar coordinate programming, equidistant compensation are directly related to this selection.
Motion Paths (Interpolation Types)
Linear interpolation involves moving in a straight line in three-dimensional space. Before starting interpolation calculations, the TNC determines the length of the path based on the programmed coordinates. In the process of movement, the control of the contour feed is carried out so that its value does not exceed the allowable values. Movement along all coordinates must be completed simultaneously.
With circular interpolation, the movement is carried out along a circle in a given work plane. The parameters of the circle (for example, the coordinates of the end point and its center) are determined before the start of the movement, based on the programmed coordinates. In the process of movement, the control of the contour feed is carried out so that its value does not exceed the allowable values. Movement along all coordinates must be completed simultaneously.
Helical interpolation is a combination of circular and linear interpolation.
Linear interpolation at rapid traverse - G00, G200. During rapid motion, the programmed motion is interpolated and the movement to the end point is carried out in a straight line at the maximum feedrate. Feedrate and feedrate, for at least one axis, are maximum. The feedrate of the other axes is controlled so that the movement of all axes ends at the end point at the same time. While the G00 instruction is active, the movement decelerates to zero in every block. If it is not necessary to decelerate the feedrate to zero every block, then G200 is used instead of G00. The value of the maximum feedrate is not programmed, but is set by the so-called "machine parameters" in the memory of the CNC system. G00, G200 instructions are modal.
Linear interpolation with programmed feedrate - G01. Movement at the specified feedrate (in F word) towards the end point of the block is carried out in a straight line. All coordinate axes complete the movement at the same time. The feedrate at the end of the block is reduced to zero. The programmed feedrate is a contour feedrate, i.e. the feedrate values for each individual coordinate axis will be smaller. The feedrate value is usually limited by the setting of "machine parameters". Word combination variant with G01 instruction in the block: G01_X_Y_Z_F_.
Circular interpolation - G02, G03. The block is traversed in a circle at the contour speed specified in the active F word. Movement along all coordinate axes is completed simultaneously in the block. These instructions are modal. The feed drives specify a circular movement at the programmed feed in the selected interpolation plane; the G02 instruction specifies clockwise movement, while the G03 instruction specifies counterclockwise movement. When programming, a circle is defined using its radius or the coordinates of its center. An additional circle programming option is defined by the G05 instruction: circular interpolation with tangential path entry.
Programming a circle using a radius. The radius is always given in relative coordinates; in contrast to the end point of the arc, which can be specified in both relative and absolute coordinates. Using the position of the start and end points, as well as the value of the radius, the TNC first determines the coordinates of the circle. The result of the calculation can be the coordinates of two points ML, MR, located respectively to the left and to the right of the straight line connecting the start and end points.
The location of the center of the circle depends on the sign of the radius; with a positive radius, the center will be on the left, and with a negative radius, it will be on the right. The center location is also determined by the G02 and G03 instructions.
Variant of a word combination with a G03 instruction in a block: N_G17_G03_X_Y_R±_F_S_M. Here: instruction G17 means to select circular interpolation in the X/Y plane; the G03 instruction defines circular interpolation in the counterclockwise direction; X_Y_ are the coordinates of the end point of the circular arc; R is the radius of the circle.
Programming a circle using the coordinates of its center. The coordinate axes relative to which the position of the center is determined are parallel to the X, Y and Z axes, respectively, and the corresponding center coordinates are named I, J and K. The coordinates set the distances between the starting point of the circular arc and its center M in directions parallel to the axes. The sign is determined by the direction of the vector from A to M.
N… G90 G17 G02 X350 Y250 I200 J-50 F… S… M…
Full circle programming example: N… G17 G02 I… F… S… M…
Circular interpolation with tangential access to a circular path - G05. The CNC uses the G05 instruction to calculate such a circular section, which is reached tangentially from the previous block (with linear or circular interpolation). The parameters of the formed arc are determined automatically; those. only its end point is programmed, and the radius is not specified.
Helical interpolation - G202, G203. Helical interpolation consists of circular interpolation in the selected plane and linear interpolation for the remaining coordinate axes, up to a total of six rotary axes. The circular interpolation plane is defined by the G17, G18, G19 instructions. Clockwise circular movement is carried out according to the G202 instruction; counterclockwise circular motion - G203. Circle programming is possible both using the radius and using the coordinates of the center of the circle.
N… G17 G203 X… Y… Z… I… J… F… S… M…
CSS -P and second, it is only supported by Netscape browsers.And him programming in JavaScript, it's a minefield between the two major browsers. When viewing these pages, please be aware that each browser loads its own property description page. positioning and programming these properties.
Until the advent of CSS-P, the only means of relatively accurate positioning there were tables. They made it possible to accurately position the components of an HTML page relative to each other on a plane. CSS-P allows you to accurately place the markup element not only relative to other components of the page, but also relative to the page boundaries.
In addition, CSS-P adds another dimension to the page - markup elements can "run into" each other.
In this case, you can change the order of "collision" - shift the layers. To verify this, it is enough to use the link from the above example.
But that's not all.
Layers can be developed. (open)
Rice. 5.1.
Rice. 5.2.
The term "layer" instead of "block" markup element" is used here for the reason that it better reflects the effect that is achieved by positioning, and not at all to spite the supporters of Microsoft.
Now let's move on to the discussion of attributes. positioning. (open)
Rice. 5.3.
Rice. 5.4.
Coordinates and dimensions
The CSS-P standard allows for pixel-accurate placement of a block markup element in the working field of the browser window. With this approach, a natural question arises: how does the coordinate system work, in which the author of the page arranges the placement of its components.
CSS-P defines two coordinate systems: relative and absolute. This allows you to provide flexibility in the placement of elements both relative to the boundaries of the working field of the browser window, and relative to each other.
Blocks are not abstract points that do not take up space on the page plane. Blocks are rectangles that "sweep" an area. The text and other page components under the block become inaccessible to the user, so linear dimensions block are no less important for creating HTML pages than its coordinates .
Using " absolute" coordinates, the reference point is placed in the upper left corner of the parent box (for example, the browser window), and the X and Y axes are directed to the right horizontally and down vertically, respectively:
Rice. 5.5.
If, in this coordinate system, some block element should be placed 10 px below the top edge of the browser client area and 20 px to the right of the left edge of the browser client area, then its description will look like this:
Example ( position:absolute;top:10px; left:20px; )
In this entry, the type of coordinate system is set by the position attribute (value - absolute ), the X coordinate is set by the left attribute (value - 20 px ), the Y coordinate is set by the top attribute (value - 10 px ).
The top and left attributes define the coordinates of the block 's top left corner in absolute coordinates . (open)
Rice. 5.6.
Coordinate values can also be negative. To remove a block from the displayed area with linear dimensions 100 px (height) by 200 px (width) is enough position its like this: (open)
Example ( position:absolute; top:-100px;left:-200px; width:200px;height:100px; )
Rice. 5.7.
Absolute positioning is used when either the entire content of the page must be accessible without scrolling ("scrolling"), or when markup elements are at the beginning of the page and their relative position is important from a design point of view, for example, to use pop-up menus.
This coordinate system allows you to place blocks on the page in the coordinates of the block that encloses them. The advantages of such a coordinate system are obvious: it allows you to save the relative position of the markup elements at any size of the browser window and its default settings.
As a starting point in this coordinate system the placement point of the current block is selected by default. The X axis is directed horizontally to the right, and the Y axis is directed vertically down.
To set the coordinates of a block, this system uses a record like: (open)
Rice. 5.8.
To work with relative system coordinates, it is better to use universal DIV blocks. This is because in Netscape Navigator, for example, a paragraph cannot contain paragraphs. Any block immediately closes the paragraph, so you can't put anything inside it.
IN relative system
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