GB 7931-1987 1:500, 1:1 000, 1=2000 topographic map aerial photogrammetry field specifications
Some standard content:
National Standards of the People's Republic of China
1:500.1:1000.1:2000 Topographic Maps Aerial Photogrammetry Field Work Specifications
Specifications for aerophotogrammetric field work1:500,1:1000,1:2000 topographicmapsUDC528.7(203 ) | | tt | Topographic maps measured in accordance with this specification can be used by various departments of the national economy for survey, planning, design, etc. 1 General principles
1.1 Specifications of topographic maps
1.1.1 Coordinates, elevation systems and Projection
1.1.1.1 The coordinate system temporarily uses the 1954 Beijing coordinate system, or an independent coordinate system can be used. The elevation system adopts the 1985 National Elevation Datum; when an independent elevation system is used, try to jointly measure with the 1985 National Elevation Datum. 1.1.1.2 Plane control adopts Gauss-Krüger projection and calculates the plane rectangular coordinates according to 3° zones. When there are special requirements for the control network, any longitude can be used as the independent coordinate system of the central meridian, and the projection surface can also use the local average elevation surface. 1.1.2 The layout and numbering of topographic maps
1.1.2.1 The layout of topographic maps shall be square or rectangular, with specifications of 50cm×50cm or 40cm×50cm. 1.1.2.2 Numbering method of map frames: The map numbers are always numbered according to the coordinate kilometers of the southwest corner of the gallery, with the front and back connected by a short line in the middle. Strip survey areas or small area survey areas can be numbered in the same order as the survey areas. 1.1.3 Classification of terrain categories
Flat land: most areas with a ground slope below 2°; hilly land: most areas with a ground slope between 2° and 6°; mountainous land: most of the ground Areas with slopes between 6° and 25°; Alpine areas: most areas with ground slopes above 25°. 1.1.4 Basic contour distance
Contour distance is selected according to the requirements of terrain type and map use, as specified in Table 1. Table 1
Basic contours
Scale
1:500
1:1000
1:2000
Terrain category|| tt||Flat land
0.5
0.5(1.0)
1.0(0.5)
Note: The contour distances in brackets need to be selected according to the drawing (the same below) . Hilly land
1.0(0.5)
1.0
1.0
Mountain land
1.0
1.0
2.0(2.5)
m
Alpine
1.0
2.0
2.0(2.5)
-Only one basic contour is used in the picture When the basic contour distance cannot show the landform features, half-distance contour lines should be drawn. Released by the National Bureau of Standards on June 10, 1987
Implemented on 1988-01-01
GB7931-87
In flat areas, according to the needs of the map, contour lines may not be drawn, only Represented by elevation point annotation. 1.1.5 Density of elevation note points
Elevation note points are generally selected on obvious feature points or terrain points. According to the terrain type and the number of feature points and terrain points, the density is every 100cm on the map. 5~20 within.
1.1.6 Topographic map symbols and annotations
Implement the provisions of GB7929-87 "1:5001:1000, 1:2000 Topographic Map Schema". 1.2 Accuracy of topographic map
1.2.1 The plane position error of the feature points
The plane position error of the feature points on the map to the nearest field plane control point or horizontal height control point shall not be greater than the table 2 regulations. Table 2
Medium Error
Project
Geographical Points
Terrain Category
1.2.2 Medium Error in Elevation of Elevation Note Points and Contour Lines Flat hilly land
0.6
Mountain and high mountain land
0.8
Table 3 specifies. Table 3
Scale
Terrain Category
Error in Note Points
Error in Contours
Flatland
0.2||tt ||0.25
1-500
Hillland
0. 4
(0.2)
0.5
(0.25)|| tt||Mountain
0.5
0.7
Alpine
0.7
1.0
Flatland
0.2||tt ||(0.4)
0.25
(0.5)
1:1000
Hillland
0.5
0.7||tt| |Mountains
0.7
1.0
High mountains
1.5
2.0
Flatlands
0.4
(0.2)
0.5
(0.25)
1:2000
hilly
0.5
0.7
mountain
1.2
1.5
mm
m
Alpine
1.5
2.0
1: The ground slope of the 500 topographic map alpine areas is above 40°, the 1:1000 topographic map alpine areas, the 1:2000 topographic map mountains, and the high mountain areas cannot be directly found on the map. To measure the accuracy of the contour elevation, the formula can be used ( 1) Calculation: a+btgα
In the formula: a The elevation error of the elevation note point, m; b --- The error of the plane position of the ground object point, m; The ground slope near the inspection point, ( ). 1.2.3 Accuracy requirements in difficult areas
The plane and elevation errors in difficult areas (such as forest areas, shadow-covered areas, etc.) can be relaxed by 1/2 according to Table 2 and Table 3. 1.2.4 Maximum error It is specified that twice the error in
is the maximum error.
1.2.5 On the premise of meeting the drawing accuracy of this specification, and with the approval of the superior authority, operating methods not included in this specification may be used. 1.3 Density requirements of basic control points
(1)
1.3.1 The control points that can be used as the starting and closing points of the first-level photo control base measurement are called basic control points. Plane basic control points include national-level triangular points, precision conductor points, 5-second-level small triangular points and conductor points; elevation basic control points include national-level leveling points and out-of-class leveling points. 1.3.2 The density of plane foundation control points in the survey area should be such that there is at least one point for every four map areas; the density of elevation foundation control points should be such that there is at least one point within 2 to 4 km.
1.4 Requirements for aerial photography data
Implement the regulations of GB6962-86 "Aerial Photography Specifications for Topographic Maps at Scales of 1:500, 1:1000, and 1:2000". The aerial photographic scale should be reasonably selected according to the instrument equipment, mapping method, mapping accuracy requirements, etc. Generally, the ratio k of the scale denominator of the flat and hilly terrain photograph GB793187
to the denominator of the mapping scale is 4 times appropriate. , the k value in mountainous and alpine areas is preferably 5 to 6 times. When the map is urgently needed and the k value is greater than 6 times or up to 8 times, necessary technical measures must be taken to ensure that the accuracy of the map complies with the requirements of this specification. 1.5 Preparation
A series of preparations are required before operation to ensure normal working procedures. 1.5.1 Do a good job in collecting various data, mainly including the following: a. Aerial photography data;
b.
Basic control point results;
Various map data, such as Various old topographic maps, traffic maps, water conservancy maps, administrative division maps, gazetteers, etc. c.
1.5.2 For areas with unfamiliar conditions, a survey of the survey area should be conducted to understand all aspects related to production and life in the survey area to ensure the smooth progress of the work.
1.5.3 Prepare the survey area technical design document (including editing instructions) in accordance with relevant regulations. 1.5.4 All instruments and equipment used in operations must be inspected and calibrated. 2 Layout of control points
2.1 General provisions
2.1.1 Field control points are the basis for encrypted control points and survey maps in the aerial survey industry, and are divided into three types: plane control points, elevation control points, and level-height control points.
Plane control point only measures the plane coordinates of this point. A height control point only measures the height of that point. For level and height control points, the plane coordinates and elevation of the point must be measured. 2.1.2 The layout of control points should meet the following photo conditions: a. Generally, it should be laid out within the overlapping range of six or five pieces in the heading and side direction, so that the deployed control points can be as common as possible. b. The distance between the control point and the edge of the image shall not be less than 1cm (18cm×18cm image frame) or 1.5cm (23cm×23cm image frame). The distance between the control points of the comprehensive method map and the heading edge shall not be less than 1/2 as specified above. c. The distance between the control points and various marks on the image should not be less than 1mm. d. The control point should be selected near the side overlap center line, and the distance from the azimuth line should be greater than 3cm (18cm×18cm image frame) or 4.5cm (23cm×23cm image frame). When the side overlap is too large to meet the requirements, points should be placed separately. When the points on adjacent routes cannot be shared due to small side overlap, points can be distributed separately. At this time, the vertical distance split by the control range should be less than 1cm, and in difficult cases, it should not be more than 2cm. 2.1.3 If the scope of the survey area is divided according to the gallery line, the control points located on the free map edge, the map edge to be formed, and the map edges formed by other methods must be arranged outside the gallery line to ensure that the map is full. If the survey area is divided according to the required range, the guaranteed map range shall prevail. 2.2 Entire field distribution
2.2.1 Entire field distribution mapped by the comprehensive method
When the map scale is not greater than four times the aerial photography scale, each of the four corners of the mapping area of ??every number of photos Lay out a flat high point and set up a flat high point near the main point for inspection (Figure 1). If the map scale is four times greater than the aerial photography scale, control points should be added. o | | tt | .2 The all-out-of-field layout using the omnipotent method
a. During stereo mapping or differential correction, four flat height points are arranged for each stereo image pair. When the map scale is four times greater than the aerial photography scale, a flat high point should be added near the main point (Figure 2). GB7931-—87
b. If the plane position of the control point is completed by in-house densification, and only the elevation part is measured in the field, the level control point in Figure 2 will be changed to an elevation control point.
2.2.3 In addition to meeting the general regulations, the position of the point on the image must also meet the following requirements: the point is no more than 1cm away from the straight line passing through the main point of the image and perpendicular to the azimuth line. In difficult cases, individual points Can be no larger than 1.5cm. If a photo (two three-dimensional image pairs) covers a picture, the four basic correction points, or orientation points, should be selected as close as possible to the gallery points and figure lines, and generally as far away from the gallery points and figure outlines as possible. The line is within 1cm.
2.3 Route Network Distribution Points
2.3.1 Route Network Distribution Points should have six high-level points arranged according to each segment of the route (Figure 3). ?
Figure 3
2.3.2 The number of baseline intervals between the first and last points can be implemented by referring to Appendix A. 2.3.3 The upper and lower control points at the beginning and end of the route should be located as far as possible on a straight line passing through the main image point and perpendicular to the bearing line. In difficult circumstances, the deviation from each other should generally not be greater than half the baseline. The upper and lower pairs of points should be arranged in the same three-dimensional image pair. 2.3.4 The two control points in the middle of the route should generally be arranged on the center line of the first and last control points. When it is difficult, you can deviate from the baseline by about 1 to both sides, and strive to have one of them on the midline. Try to avoid the two control points deviating to the same side of the midline at the same time. If there is a deviation on the same side, the maximum should not exceed 1 baseline.
2.4 Regional network distribution points
2.4.1 The regional network should not include routes and image pairs with overlapping images that do not meet the requirements, and should not include large cloud shadows, shadows, etc. that affect internal encryption The network connection is like a pair.
2.4.2 Whether it is a flat network or a flat-high network, the route span and the number of baselines between control points generally do not exceed the requirements in Table 4. Table 4
Scale
Number of routes, bar
Number of baselines between level and height control points, bar
Number of baselines between elevation control points, bar
1 :500
4~5
4~6
2~4
1:1000
4~5
6~7
2～4
1+2000
5~6
6~10
4~6
1: 500 topographic map For flat land and hilly land, all field points are laid out at all levels, and for flat land on 1:1000 and 112000 topographic maps, all field points are laid out at all elevations.
2.4.3 The control points of the area network can be laid out according to the specific situation: when the area network is used to encrypt plane control points, 6 or 8 flat high points can be laid out along the perimeter (Figure 4, Figure 5). o
Figure 4
O
Figure 5
GB7931-87
b. When the area network is used to encrypt the level control points, along the perimeter Lay out 6 or 8 flat high points. Span of elevation control points: When 1:2000 is mapped, the route direction is separated by 4 to 6 baselines (Figure 6); for 1:500 and 1:1000 maps, it is best to use all-outfield distribution points for elevation control points. When encrypted, the span is 2 to 4 baselines. ·Elevation points
Figure 6
c. Due to terrain and other conditions, irregular regional grid points can also be used. Generally, high points are placed on protrusions and elevation points are placed on concave places. When the distance between the concave corner point and the convex corner point exceeds two baselines, a flat high point should also be arranged at the concave corner (Figure 7). Q | 2.5 Point layout under special circumstances
2.5.1 Point layout at the junction of aerial photography areas
At the junction of aviation areas or aerial photography zones, control points should be laid out at the overlapping junctions of routes, and adjacent areas should be shared as much as possible. If the public requirements cannot be met, points should be distributed separately.
2.5.2 Placement of points with insufficient course overlap
When the course overlap is less than 53% of the overlap, it is regarded as an aerial photography vulnerability, and points must be laid out separately. The flatbed instrument mapping method is used for supplementary testing of the loopholes. .
2.5.3 Points with insufficient side overlap
When the side overlap is less than 15%, points must be placed separately. If the re-examination part is larger than 1cm, the image is clear, and there are no important features within the range, 23 additional elevation points can be measured in the overlapping part. Otherwise, the part with insufficient overlap should be re-measured using the flatbed instrument mapping method. 2.5.4 If the main point or standard point falls into the water, it will be regarded as a point if the main point or standard point is in the water area, or is covered by cloud shadows, shadows, snow shadows, etc., or has no obvious surface objects. Falling into the water. When the size and location of the falling water range do not affect the connection of the three-dimensional model, points can be arranged according to the normal route. b. When no obvious target can be selected within 2cm of the main image point, or no connection point can be selected within the overlapping range of the three headings, the falling water image corresponds to the entire field layout.
c. The standard position of the orientation point is near the water landing area. At this time, if the connection point cannot be selected within the overlapping range of the three headings beyond 4cm (23cm×23cm image frame) or 2.5cm (18cm×18cm image frame) away from the azimuth line, then The falling water image corresponds to the entire outdoor layout. 2.5.5 Waterfront and island distribution points
Waterfront and island areas are generally distributed in the entire field, based on the principle of maximizing the control of the surveying and mapping area. The land portion beyond 1cm beyond the line connecting the control points should be measured with level points. If difficult, it can be changed to elevation points. If it is difficult to ensure accuracy using aerial surveying methods, flat-panel surveying methods can be used for supplementary surveying.
3 basic control measurement
GB7931-87
In addition to using national grade points, it can also be reasonably laid out according to the actual situation and specific requirements of the survey area. The error in angle measurement is 5 \'s small triangular points and conductor points, as well as the measurement level, serve as the basis for image control measurement. For small measurement areas using an independent coordinate system, a 5-second-level small triangular network and wire network can also be laid out as the basis for photo plane control measurement. 3.15 seconds plane control measurement
3.1.1 Small triangulation
3.1.1.1 Layout form of small triangular points
The layout of small triangular points is based on national grade points, using interpolation It is implemented by methods such as net (lock) and insertion point. Small triangular points can also be used as basic controls in independent coordinate systems to independently form linear locks, triangular nets, etc. The edge measurement work in the network can be completed using photoelectric distance meters with corresponding accuracy.
3.1.1.2 The measurement accuracy and specifications of the small triangular points should comply with the provisions of Table 5. Table 5
Error in angle measurement
5″
3.1.1.3 Insertion network and insertion point
Starting side length
Relative middle error
1/40000
Weakest side length
Relative middle error
1/20000
DJ2
2
Number of horizontal angle measurements
DJe
6
Plug into the network and strive to lay out Evenly hooked, the internal angles of each triangle are generally not less than 30°, and individual internal angles in the middle of the comprehensive net can be not less than 20°. The intersection angle of the insertion point should not be less than 30°. The average side length of the intersection is generally 1.5km for 1:1000 survey maps, and the maximum is no more than 2km. For 1:2000 survey maps, it is generally 3km, and the maximum is no more than 4km. The sides of the plug-in network and the plug-in point should be observed facing each other as much as possible. 3.1.1.4 Linear lock
Linear locks are required to be laid out in a nearly straight extension as much as possible, and the triangles in the lock should be as equilateral as possible. The distance angle of the lock is generally not less than 40°, and the sum of the graphic strength coefficients should be less than 85. The average side length of a triangle is 0.5km on a 1:500 map, 1km on a 1:1000 map, and 2km on a 1:2000 map.
3.1.2 Photoelectric ranging wire measurement
3.1.2.1 The layout form of photoelectric ranging wire points can be arranged into attached wires, node wires or wire networks. The conductor route should be laid out as straight as possible between grade points, between grade points and nodes, and between nodes and nodes. Adjacent sides of the conductors should be as equal as possible. 3.1.2.2 The main technical requirements for photoelectric ranging wire measurement are specified in Table 6. Table 6
Error in angle measurement
5
Note: n is the number of turning angles.
average side length
mm on the picture
1000
500
300
number of sides
8||tt ||12
18
azimuth
closure error
10%
full length phase of conductor
closure error||tt| |1/20000
1/15000
1/14000
Number of horizontal angle measurements
DJ2
2
DJ.
6
3.1.2.3 The allowed number of edges between the node and the starting point is 0.7 times the number of edges specified in Table 6; the allowed number of edges between nodes is Table 6 1/2 of the specified number of sides.
3.1.2.4 Before each use, the photoelectric distance meter and its main accessories should be inspected according to the needs and the actual condition of the instrument. 3.1.2.5 Operational requirements for photoelectric distance measuring wires: The nominal accuracy of the photoelectric distance meter used is required to be 1km, and the error in distance measurement is not greater than 10mm; a.
b.
Distance measurement working requirements Carry out under the conditions of stable atmosphere and clear imaging; c.
d.
GB7931--87
During the ranging process, if the atmospheric end flow is seriously affected, Observation should be stopped; the number of slant distance measurements should be no less than two. One measurement should be read at least twice. When the difference between the two readings is less than 1cm, the average should be taken as the value of the measurement;
e.| |tt||The difference between the single-way measurements of the slope distance is generally not greater than 15mm; the meteorological data is measured once on each side, the temperature reading is read to 1℃, and the air pressure reading is read to 1mm mercury height; f.
g. Generally, the tripod method is used for testing.
3.1.3 Point Selection and Burial Stone
The point selection of 5-second basic control points should be carried out in accordance with the specific layout plan stipulated in the technical design document. After the point location is determined, stones can be buried as needed, and generally no markings are required. The roll call can be numbered according to the order of the survey area, or the nearby geographical name can be used. See Appendix B for the stone embedding specifications for the 5-second level basic control points. 3.1.4 Horizontal angle observation
3.1.4.1 Horizontal angle observation generally adopts the full circle direction observation method. When the number of directions is more than three, it must be reset to zero, and when it is more than seven, it must be grouped; the number of directions in each group should be as equal as possible, and the same starting direction should be used. The dial should change position by 180%/n between each measurement round (n is the number of measurement rounds). 3.1.4.2 The observation tolerance of the horizontal angle shall not exceed the requirements in Table 7. Table 7
Instrument level
Tolerance category
Half-measurement regression zero difference
Change range of 2C
Poor in each measurement return in the same direction| |tt||Triangular misclosure
DJ2
12\
18
12
15\
DJ
24 * | When retesting, the same starting direction should be measured jointly. When the zero return difference, the 2C variation range of the starting direction exceeds the limit, or the number of remeasured directions in a measurement round exceeds 1/3 of the total number of directions, the measurement round will be retested. When the number of retested rounds exceeds 1/2 of the total number of measured rounds or retesting occurs due to the closure error exceeding the limit, all measurement stations should be retested. 3.1.4.4 When the eccentricity of the measuring station and aiming point is greater than 1/80000 of the distance from the measuring station to the nearest observation point, centering correction should be performed in the horizontal direction. When measuring the centering element, the eccentricity should be measured to millimeters and the eccentricity angle should be measured to 15'. The length of the side of an error triangle projected in three directions or the diagonal length of an error quadrilateral projected twice in two directions should not be greater than 5 mm. 3.1.4.5 The adjustment calculation and positioning shall be carried out according to the provisions of Table 8. Table 8
Observation direction value
1\
Correction number of each item
1
Logarithm or function
6 digits|| tt||Coordinate calculation
m
0.001
3.1.4.6 The following limits should be checked and calculated for field observation data: a.
b.|| tt||c.
The angle measurement error m of small triangulation measurement is calculated according to the following formula: mg=±[W]/3n
The angle measurement error m of wire (network) measurement? According to Calculate with the following formula: mg二人
ffei
LN. N
The formula for calculating the square of the azimuth conditional closure W and the polar condition closure W: W#≤10\n
Last coordinates
0. 01
Coordinates Azimuth angle
1
(2)
(3)
·(4)
where: w.
n-
Triangle closure error, (\);
GB7931--87
10\
The number of triangles or the number of transferred azimuth angles; f. Azimuth angle closure of an attached wire or closed loop, (\); N. - Calculate the number of measuring stations for f;
N - the number of attached wires and closed loops; 8 find the logarithmic second difference of the sine of the distance angle one by one (in the 6th logarithmic digit). 3.2 Elevation control survey
3.2.1 Contour leveling
As the basic control survey, the contour line should start from the national grade leveling point. 3.2.1.1 Out-of-class leveling generally adopts the single-pass observation method. The branch line level should be measured by round-trip observation or one-way double measurement. (5)
3.2.1.2 The measurement accuracy and specifications of external leveling measurements shall be in accordance with the provisions of Table 9. When mapping at a height of more than 1m is used on flat or hilly land, the total route length can be appropriately lengthened.
Table 9
Route length, km
Terrain category
Adhesion
Flat hilly land
Mountain land
12 | | tt | | 20 | Branch line
3
6
According to the route or closed
Route elevation closure difference
mm
30
45
Distance from instrument to scale
m
100
3.2.1.3 The observation work of external leveling measurement should generally be done intermittently on fixed marks. If this is not possible, it should be done intermittently on three wooden stakes driven into the ground. When the height difference between the two intermittent points before and after the interval is not greater than 6mm, you can continue to observe forward. 3.2.1.4 The observation tolerance for out-of-class leveling measurements should be less than the requirements in Table 10. Table 10
Same scale black and red
Difference in surface height difference
mm
4
3.2.2 Triangular elevation route measurement
Two heights at the same station
Difference of difference
mm
6
Before and after one station
Sight distance Difference
20
Sight distance before and after
Sum of difference
m
100
Sight away
Obstacles|| tt||m
0.2
According to the actual situation, the triangular elevation measurement method can be used to determine the 5-second level basic control point elevation in hilly and mountainous areas. The starting and closing points of the triangular elevation route should be elevation points not lower than the joint measurement of the contour level. 3.2.2.1 The accuracy and specifications of triangular elevation route measurement shall be in accordance with Table 11. Average side length
km
0.5
1.0
2.0
Item
Number of sides, bars
Contour distance
m
1.0
30
15
4
Contour
m
2.0
40
30
15
GB7931-—87
Table 11
Route full length and height
Cheng closed Difference
m
0. 05ESSj
Note: S is the route length, km; if it is less than 1km, it will be counted as 1km. Round trip height measurement
Poor difference
m
0.1s
3.2.2.2 If the route is laid in the form of nodes, the requirements are the same as those in 3.1.2.3. Number of vertical angle measurement rounds
(Medium wire method)
DJ2
2
DJ
4
Vertical angle of each measurement round|| tt||Poor and same test
Poor site index difference
DJ2
15
DJ.
25*
3.2 .2.3 The sighting positions when observing in all directions should be recorded in the handbook. When observing the same point from different directions, you should aim at the same position. If you encounter special circumstances, you can choose another aiming position, but you must have a diagram in your hand to illustrate it. 3.2.2.4 The elevation and instrument height shall be measured twice with a steel ruler and read to 5mm. The difference shall not be greater than 1cm. When the standard is high, the difference shall not be greater than 2cm. 3.2.2.5 Vertical angle observations should generally be carried out when the target is clear and the atmosphere is stable. When there are many directions, they can be grouped for observation. When the visibility conditions are poor, continuous observation can also be carried out in each direction. 3.2.3 Photoelectric ranging elevation wire measurement
Photoelectric ranging elevation wire can replace the external level measurement. 3.2.3.1 Layout form of photoelectric ranging elevation conductors: Photoelectric ranging elevation conductors can be laid out in the form of attached conductors, node conductors or conductor networks. The photoelectric ranging elevation conductor can be measured alone or simultaneously with the photoelectric ranging plane conductor. 3.2.3.2 The measurement accuracy and specifications of the photoelectric ranging elevation conductor should comply with the provisions of Table 12. 3.2.3.3 Operational requirements for photoelectric ranging elevation conductor measurement: In addition to completing the distance measurement work according to the requirements of 3.1.2.5, when measuring the photoelectric ranging elevation conductor, the following provisions should also be implemented: a.||tt| |b.
upper;
c.
d.
positive.
The vertical angle must be straight back to the gauge;
It is best to choose the line of sight in the same area with the ground cover to avoid passing over the thermal body, and it should be 1.3m away from the ground or obstacles to the height of the instrument and the gauge elevation Measure to millimeters;
If using DJ. When measuring the zenith distance (or vertical angle) with an instrument, the vertical dial eccentricity should be measured first and modified in the observation results. Table 12
Item
Average side length
300| |tt||500
1000
Contour distance
0.5m
18
12
Note: ①s is the side length, km.
②n is the number of sides.
Number of sides, strips
Contour distance
1.0m
40
20
8
Contour distance
2.0m
60
30
20
round-trip height measurement of the full length of the route
closure difference
mm
24/n
30n
70n
Poor difference
m
0.2S
Number of vertical angle measurements
(Medium wire method)
DJ
DJs
4
Vertical angle of each measurement round
Poor and the same direction|| tt||Poor indicator spread
DJ2
15″
DJs
25″
5m
18
12
Note: ①s is the side length, km.
②n is the number of sides.
Number of sides, strips
Contour distance
1.0m
40
20
8
Contour distance
2.0m
60
30
20
round-trip height measurement of the full length of the route
closure difference
mm
24/n
30n
70n
Poor difference
m
0.2S
Number of vertical angle measurements
(Medium wire method)
DJ
DJs
4
Vertical angle of each measurement round
Poor and the same direction|| tt||Poor indicator spread
DJ2
15″
DJs
25″
5m
18
12
Note: ①s is the side length, km.
②n is the number of sides.
Number of sides, stripwwW.bzxz.Net
Contour interval
1.0m
40
20
8
Contour interval
2.0m
60
30
20
Round trip height measurement of the entire route
Closure difference
mm
24/n
30n
70n
The difference is poor
m
0.2S
Number of vertical angle measurement rounds
(middle wire method)
DJ
DJs
4
The vertical angle of each measurement round
is poor and the index difference in the same direction
DJ2
15″
DJs
25″
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