Manual of Military Training - James A. Moss (read dune .TXT) 📗
- Author: James A. Moss
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For example, suppose your stride is 66 inches long (33 inch pace) and you wish to make a sketch on a scale of 3 inches = 1 mile. The R. F. of this scale is 3 inches/1 mile = 3 inches/63360 inches = 1/21120. That is 1 inch on your sketch is to represent 21120 inches on the ground. As you intend to measure your ground distances by counting your strides of 66 inches length, 1 inch on the sketch will represent as many of your strides on the ground as 66 is contained into 21120 = 320 strides. For convenience in sketching you wish to make your scale about 6 inches long. Since 1 inch represents 320 strides, 6 inches will represent 6 × 320 = 1,920 strides. As this is an odd number, difficult to divide into convenient subdivisions of hundreds, fifties, etc., construct your scale to represent 2,000 strides, which will give it a length slightly in excess of 6 inches—6.25. Lay off this length and divide it into ten main divisions of 200 strides each, and subdivide these into 50 stride divisions as explained in Par. 1862.
1889. Position sketching. The following are the instruments used in position sketching:
Drawing board with attached compass (Fig. 2); Loose ruler, on board (Fig. 2); Rough tripod or camera tripod; Scale of M. D.'s (shown on ruler, Fig. 2); Scale of sketchers, strides or paces (at six inches to one mile), on ruler; Clinometer (not necessary if board has slope board, Fig. 6); Scale of hundreds of yards shown on ruler; Scale of paces. Methods to be used(1) Select a base line,—that is, a central line 1/4 to 1/2 mile long in the area to be sketched. It should have at its ends some plainly marked objects, such as telegraph poles, trees, corners of buildings, etc., and from its ends, and intermediate points, a good view of the area should be possible. The base line selected should be capable of being measured.
(2) Set up, level and orient the drawing board at one end of the base (A), Fig. 1, Y, for example. Draw a meridian on the sheet parallel to the position of the magnetic needle. Assume a point (A), Fig. 1, Y, corresponding to the ground point (A), 890, on the sheet, in such a position that the area to be sketched will lie on the sheet.
(3) Sight at hilltops, stream junctures, stream heads, etc., to begin the locations of these points by intersection, labelling each ray so as to be able to identify it later.
(4) Traverse to (b) and complete the locations by intersection as previously explained. If the base line is not accurately measured, the map will be correct within itself in all of its proportions, but its scale will not necessarily be the scale desired.
(5) Draw the details of the country between A and B and in the vicinity of this line, using the conventional signs for roads, houses, etc.
(6) The lines from station (b), Fig. 1, X, to any of the other located points may now be used as a new base line to carry the work over additional area.
(7) In case parts of the area are not visible from a base line, these parts are located by traversing as before explained.
(8) Having learned by several repetitions the above steps, the sketcher will then combine contouring with his horizontal locations.
1890. Outpost sketching. The same instruments are used as in position sketching, and so are the methods the same, except that the sketcher cannot advance beyond the outpost line, toward the supposed position of the enemy. It is often possible to select a measurable base line well in rear of the line of observation,—for instance, along the line of resistance. Secondary base lines may then be taken on or near the line of observation, from the extremities of which additional base lines may be selected, if necessary, and points toward the enemy's position located by intersection. Details are sketched in as in position sketching. For obvious reasons, no traversing should be done along the line of observation.
1891. Road sketching. The following are the instruments used in road sketching:
Drawing board or sketching case; Loose ruler; Scale of strides, or paces, if made dismounted; scale of time trotting or walking, if mounted; Scale of hundreds of yards, at three inches to 1 mile; Scale of M. D.'s; Slope board (if clinometer is not available). Methods to be used(1) At station 1, Fig. 10, orient the board as described in par. 1872, holding the board in the hands, in front of the body of the sketcher, who faces toward station 2.
(2) Important points in the vicinity, such as the railroad bridge, the stream juncture, hilltops, are sighted for intersections, lines drawn as shown and the sketcher traverses to station 2.
(3) At station 2 he locates and draws in all details between station 1 and 2, to include about 300 yards on each side of the road.
(4) The traverse is then continued forward as described for 1 and 2.
(5) After some practice of horizontal sketching, as just described, the sketcher will be able to take up contouring in combination. The methods are as described in the paragraph on contouring.
(6) When the traverse runs off the paper as at A, Fig. 10, the following method is followed: Reorient the board so that the road forward will lie across the long dimensions of the paper; draw a meridian parallel to the compass needle and assume a point on the new sheet corresponding to the last point (A) plotted on the first sheet.
(7) On completion of the sketch various sections will be pasted together, so that all the meridians are parallel.
1892. Combined sketching. Let us suppose that we have the rectangle W, X, Y, Z, Fig. 11, assigned to us to map and that we have been given four sketching parties, and that the locations and elevations of A and B have been previously determined by triangulation and are plotted to scale on our rectangle.
A logical step would be to carefully plot the line a' b', and then the lines c' c" and c" d.
If the area is densely wooded we run "line of level" by using the slope board or clinometer and by taking elevations at points arbitrarily selected. Our lines will look something like this:
Each party will be given its rectangle with the traverses sketched in. They will each then run similar traverses over the other two sides of their area and then fill in. In this manner the whole work is tied up to the original lines.
Another methodThe line A B, Fig. 12, is carefully plotted. Each of the four sketching parties has two sketching groups. One group of party No. 1 traverses line a' Y; then the other group of the party traverses the line a" y'. The first group of party of No. 2 accompanies them. The second group of party No. 2 traverses the line c" d, accompanied by the first group of party No. 3; the second group of party No. 3, and the first group of party No. 4 traverse b" z', and the second group of party No. 4 traverses b' Z. When the first group of party No. 1 arrives at Y, it traverses Y y'. The second group of party No. 1, arriving at y', cuts the sheet along traverse and gives the first group of party No. 2 the part which shows their area; and then traverses toward Y from y'. Upon meeting the first group of party No. 1, they join forces and proceed to fill in their area.
In the same manner areas W X a' b' are filled in.
The method described above is useful in working over country which is densely wooded, and in which a general view cannot be obtained, for example, in mapping jungles.
An additional article of the sketcher's equipment is a holder for his pencils, alidade, eraser, knife, pins, etc. This consists of a series of small pockets sewed on to a piece of canvas about 7 inches by 4 inches. This can be attached to the left breast of the sketcher's coat or shirt by means of two pins. In addition to keeping all of his implements in a handy place the holder prevents the loss of the several articles. Nothing is so discouraging to the sketcher as to look for his pencil, eraser, knife or even alidade and find that he has left it several hundred yards back where he sat down last to sketch in details. By using the holder the sketcher gets into the habit of replacing articles after they are used and consequently always has them with him when needed. These holders ready made can be obtained from the Secretary, Army Service Schools at Fort Leavenworth, Kansas.
In sketching a good quality of paper should always be used as erasures will be frequent. A specially prepared paper that has the appearance of oiled paper can be obtained commercially and is excellent for sketching in damp weather. It has considerable resistance to rain. Sheets of celluloid prepared for sketching are invaluable in sketching in the rain. These are a part of the equipment of the case of sketching instruments supplied battalions in the regular army. These sheets may be procured at most any dealers.
Points for Beginners to Remember1893. 1. Always keep your pencils sharpened and have an eraser handy. No one but an expert can sketch with a dull pencil.
2. Use hard pencils when learning to sketch—4H to 6H—and go over your work afterwards with a softer pencil—2H.
3. Do not try to put down on your sketch a mass of small details that are too small to be shown on the scale at which you are sketching. For example, if you are making a sketch on a scale of 3 inches = 1 mile, do not try to show each house in a row of houses; simply indicate that there is a row of houses, by putting down several distinct conventional signs for houses in a row; nor should you try to show every little "cut" through which the road may run. Only use about one sign to the inch of telegraph or telephone lines, for wire fences, etc.
4. When first practicing sketching only plot the route over which you walk, indicating it by a single line. When you can do this with facility, go back over one of these plotted routes and fill in the woods, houses, streams and the other large features.
5. The beginner should sketch the same ground several times over—at least three or four times. Practice alone will make perfect.
6. Always try to compare your finished sketch with an accurate map of the ground, if one is obtainable. Try to practice on ground of which you can obtain a map.
7. Make each course (the distance you go between points where the direction of your route changes) as long as possible.
8. Do not try to contour until you are expert at making a sketch showing all the flat details (roads, streams, woods, houses, etc.).
9. Never try to "sketch in" the contours until you have plotted the stream lines or the direction
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