GB/T 12898-2009Specifications for the third and fourth order leveling (English PDF)

4.3 Layout principles

4.3.1 Third and fourth order leveling networks are further densified on the basis of the first and second order leveling networks. If necessary, annexed lines, loops or node networks are laid in the higher order leveling network, to directly provide elevation control points as necessary for the topographic maps and various engineering constructions.

4.4 Benchmark layout density On the third and fourth order leveling lines, it shall bury one common benchmark stone every 4 km ~ 8 km; in densely populated and economically developed areas, it can be shortened to 2 km ~ 4 km; in desert areas, the leveling branch lines can be increased to about 10 km.

4.6 Connection of new line and surveyed line

4.6.1 The starting point and end point of the newly established leveling line shall be the benchmarks of the surveyed higher or equivalent order leveling line.

4.6.2 When the newly established third and fourth order leveling line is within 4 km away from each surveyed equivalent benchmark, it shall be subject to connect leveling or adjoining leveling. In case of adjoining leveling, it shall check the surveyed benchmarks in accordance with the provisions of clause 7.8.

4.7 Technical design of leveling network

4.7.1 Prior to the deployment of the 3rd and 4th order leveling networks, surveys shall be conducted to collect geological, hydrological, meteorological and road data. The technical design is based on the existing different grades of leveling lines.

5.1 Point selection

5.1.1 Selection of leveling line Leveling line shall be laid along highways, roads and small-gradient country roads that are conducive to survey. Leveling lines shall avoid as far as possible crossing obstacles such as rivers, lakes and marshes above 500 m.

5.1.2 Selection of benchmark The benchmarks shall be selected at locations where the soil is solid, safe and secluded, convenient to observe and conducive to long-term preservation. The following points shall not be selected for benchmarks.

5.2 Stone burial

5.2.1 Mark stone types See Table 2 for the type of mark stone used in the third and fourth order benchmarks and their applicable area.

5.2.5 Land occupation and hosting of mark stones

5.2.6 Data submitted after stone burial The data that shall be submitted after stone burial includes.

7.1 Observation methods

7.1.1 The third order leveling uses the central wire reading method for round trip measurement. When using level gauges with optical micrometers and line- type invar leveling scales, one-trip double-turn point observations can also be performed.

7.2 Survey station setting requirements

7.2.1 The third and fourth order leveling uses the scale for turning point, the scale mass is not less than 1 kg. The observation shall be performed when the scale division imaging is clear and stable; if the imaging is not good, it shall appropriately shorten the length of the line of sight, until the imaging is clear and stable.

7.3.1 Optical level observation

7.3.2.3 The operating procedure for a station is as follows (taking a third order leveling as an example).

7.4 Interval and detection

7.4.1 In case of interval of observations, it is best to end the observation at the benchmark. Otherwise, it shall select two fixed points which are stable and reliable, smooth and projected, and easy to place scale from the last survey station as the interval point. If there is no fixed point, it may drive the capped wood stakes at the turn points of the last two survey stations before the interval as the interval point.

7.5 Survey station observation tolerance, digits of reading, and settings

7.5.1 The survey station observation tolerances shall be implemented as specified in Table 7.

7.6.5 The scale stake (platform) shall not be placed in a pit in order to increase the reading of the scale.

7.6.6 The number of survey stations for the direct observation and reversed observation for each leveling section shall be an even-number. When changing from direct observation to reversed observation, the places of the two scales shall be switched, and the instrument shall be reset.

7.7 Observation of nodes

7.7.1 When observing to the nodes of the leveling network, it shall make detailed records of the adjoining leveling in the observation handbook, the node adjoining leveling is in accordance with A.3.

7.7.2 Nodes located in the ground deformation area shall be subject to adjoining leveling with the local deformation observation network.

8.2 Provisions for leveling methods and tolerances

8.2.1 When using the direct rule reading method, optical micrometry, theodolite inclination method and distance measuring triangle elevation method to carry out cross-river leveling, the scope of application, and the number of observations and tolerances are to be implemented in accordance with Table

10.When the length of the sight line across the river exceeds the provisions in the above table, the methods and requirements adopted shall be specially designed in accordance with the conditions of the leveling area.

8.4 Cross-river leveling observation requirements The following requirements shall be observed in cross-river leveling observations.

8.5 Direct rule reading method

8.6 Leveling on ice Leveling for the areas in northern regions crossing rivers, swamps, water meadows, etc. can be made on the ice during winter seasons, and observe the following requirements.

9.3 Height difference calculation

9.3.1 Observational slant distance shall be subject to addition constants and multiplying constants and meteorological corrections.