5.8　Aerial Triangulation

5.8.1　Aerial triangulation shall be performed using a digital photogrammetric system.

5.8.2　For aerial triangulation，the following data should be obtained before densification:

1　Technical specifications and assessment of aerial camera；

2　Aerial photographing technical and quality inspection report；

3　Negatives or image files；

4　Index to photographs；

5　Mosaic map of flight strips；

6　Information about photo control points；

7　Information about photograph annotation；

8　Topographic maps and relevant control results data about the surveyed areas.

5.8.3　All the obtained data shall be checked and analyzed，and can only be used after being confirmed to satisfy the requirements of densification and mapping during office work.

5.8.4　The positions of densification points of each photo should be arranged according to Figure 5.8.4，the densification points shall not be less than two，and the upper and lower rows of points shall be arranged evenly.The point positions shall be selected in accordance with the provisions below:

1　The densification points shall be selected at the target points in the photograph for which the images in this photograph and its adjacent ones are clear，obvious and can be easily measured，rather than at the locations under shadow or with excessive deformation.

2　The point positions shall be in the line that passes through the principal point of photograph and is perpendicular to the heading line，with deviation on the right or left side being no more than 1.5cm.The upper and lower point should be close to the heading line.The point positions should not deviate from the standard location by more than 1cm and the elevation difference between points should not be excessive.

3　Where the lateral overlap is small，different points shall be arranged on two flight lines，provided that the sum of distances from the two points to the center line of overlap is no more than 2cm.Where the lateral overlap is so large that the selected densification points are less than 2cm apart from the heading line，different points shall be arranged on two adjacent flight lines and surveyed against each other.

4　Densification points shall be located close to the connection line of photo control points，with the perpendicular distance to the connection line being no more than 1cm.

5.8.5　For the measurement and survey of photo points，automatic match and manual adjustment should be used.

5.8.6　Where an optical camera is used for aerial photographing，photograph orientation shall be performed by means of analytic orientation of fiducial marks.Where a digital camera is used for aerial photographing，corner mark shall be used for photograph orientation.

5.8.7　The field control points shall be surveyed based on the point location sketches，point location descriptions，and positions of pin-prick holes on field control photographs.

5.8.8　The densification procedures of aerial triangulation shall have functions such as data management，flight strip networking，block pre-processing，integral adjustment，gross error detection and systematic error correction.The initial data，residual error of orientation and adjustment results shall be reflected on the printed documents.

5.8.9　The system error of photograph point coordinates may be corrected point by point with the following formulas:

Where:

x′，y′——theoretical coordinate values of fiducial marks of aerial camera，mm；

x，y——theoretical coordinate values of fiducial marks on survey photograph；

a1，a2，a3，b1，b2，b3——conversion parameters.

5.8.10　The residual vertical parallax of relative orientation and the discrepancy of model bridging shall comply with the provisions in Table 5.8.10.

Note:Δq——residual vertical parallax，mm；

Δs——discrepancy of horizontal position，m；

Δz——elevation discrepancy，m；

M——denominator of photograph scale；

f——principal distance of aerial camera，mm；

b——length of photograph baseline，mm.

5.8.11　Absolute orientation shall comply with the provisions in Table 5.8.11:

5.8.12　If the tolerances of aerial triangulation densification exceed the limits，the personnel shall conscientiously use all available data to analyze and process the calculation results of relative orientation and absolute orientation by taking into account the laws of occurrence of various errors and the magnitudes and directions of limit-exceeding error.

5.8.13　The RMSE of densification points shall be calculated using the following formula:

Where:

mcontrol——RMSE of control point，m；

mcommon——RMSE of common point，m；

Δ——discrepancy of redundant field control points，m；

d——discrepancy of common points of neighboring flight lines，m；

n——number of points for precision evaluation.