Directional corner – the geodetic name of a corner of the direction of orientation of the line on the card of rather geographical or magnetic meridian. The corner is determined directly by the local map or by a magnetic azimuth.
It is required to you
- - local map;
- - pencil and ruler;
- - protractor, artillery circle or hordouglomer;
- - compass or surveying compass.
Instruction
1. There are several ways of definition of a directional corner: according to the map or the aerial photograph by means of a protractor, a hordouglomer or an artillery circle and also on a magnetic azimuth by means of the device with a magnetic needle.
2. To define a directional corner by a protractor, find on the card a starting point and a subject on areas (reference point), note them. By means of a pencil and a ruler connect their line. Length of this line has to exceed protractor radius, beginning from a point of intersection with the vertical line of a coordinate grid.
3. Impose a protractor on the card so that "zero" on a protractor coincided with the vertical line, and the center – with a point of intersection of lines. Count a directional corner on a protractor scale on the line drawn between objects. Measurement by an artillery circle is similar to use of a protractor. The center of a circle is combined with a starting point, and a zero mark – with the northern direction of the vertical line of a coordinate grid or with the straight line parallel to it.
4. For measurement with use of a hordouglomer draw a line between a starting point and a reference point not less than 15 cm. With vertical by means of a tsirkuleizmeritel make notches of a point of intersection of this line on the lines forming an acute angle. For this purpose carry out an arch of a circle with a radius of 10 divisions of the device. Then put compasses two needles in noted points, thus, having made compasses solution equal to chord length (to distance between points).
5. Holding both needles of compasses on a horizontal line, conduct it the left needle on an extreme left vertical scale of a hordouglomer. Continue the movement until the right needle does not coincide with the line of crossing, horizontal or inclined. Remove measurement.
6. For definition of a directional corner by means of a magnetic azimuth use a compass or other device with a magnetic needle, for example, a surveying compass. To use this method, it is necessary to know the amendment of the direction. It is the size of a deviation of a magnetic meridian (magnetic needle) of the given point from the vertical line of a coordinate grid. The amendment of the direction is usually specified on the card in the form of a frame.
7. Define a magnetic azimuth which is measured clockwise from the northern direction of a magnetic meridian (direction of a magnetic needle of the device) to the defined direction. Find a directional corner on a formula: α = β + (±dα), where β – a magnetic azimuth, dα – the amendment of the direction.