Learn what is the Procedure of Photogrammetry

The photogrammetric procedure-

Project planning carries following steps:

• It Transforms project requirements to specifications concerning the area to be mapped imagined map scale and form interval. The purpose of these specifications depends on the necessary accuracy of the final map and cost constraints. More accurate maps are more expensive and take longer to collect it.
• Discover photogrammetric specifications concerning flight height, the number of images needed, the number of strips required, flight lines, estimated location for exposure sites, and equipment to use. Specifications must also develop for ground control, aerial triangulation, and compilation methodology.
• Develop a plan for aerial photography, fieldwork, and mapping compilation. The plan should coordinate with the several groups associated with the project. Crucial coordination is among the field team placing the targets and the aerial photography team. Goals should be set as close as possible to the time of photography. A project timetable with finish dates for different tasks and the estimated cost associated with them should develop as well.
• Determine the expected deliverables, including specifications on what features are to be mapped and their graphic representation.

Aerial Photography

 The steps aerial photography process consists are:

• Verification of the weather conditions that’s suitable for flying. Flying under conditions of low visibility or strong potential turbulence should be avoided. Bad climate conditions could produce not only unacceptable photographic effects but also risky for the flying crew.
• Mount the aerial camera according to the fixed procedure. Test the camera before using to ensure that it functions accurately.
• Fly the outlined routes and capture the photographs according to plans.
• Prepare the film according to specification to provide radiometrically and geometrically quality pictures.
• If required, print on the negatives the missing photo information (i.e., titles), like serial number, date, project information, etc.
• Prepare contact copies from the negatives. If needed, make enlargements that can use later, according to the requirements of the project.
• Inspect the pictures for image quality and coverage completeness. Confirm that each photograph has sufficient end laps to secure stereoscopic coverage of the whole project area. A comparable inspection should perform to confirm complete side lap coverage. Incomplete end and side lap coverage or the coverage gaps will void the complete aerial photography and need re-planning or re-flying. Another survey that should perform is recognizing the preset targets. Target inspection involves inspecting whether they are visible, appear in a stereo coverage and whether there are sufficient of them to assure reliable results. If any targets are dropping, or the whole project can’t target, points that can be recognized and surveyed on the ground should select and marked on paper copies. A copy of the prints and a summary of the chosen points should then submit to the surveying team for field measurements.
• Choose photographs that will be useful for data accumulation and develop diapositives for them.

Ground Control 

• Analyze project area for existing control. Existing control that can target and save time and money by avoiding unnecessary field surveys. Sometimes it is more cost effective to extend the aerial photography slightly exceeding the project area to combine existing control rather than to establish new control.
• Conduct field surveys as discussed above. Field surveys of selected points are necessary after the aerial photography gets completed.
• Compute and adjust the field data and establish coordinate values for the control points.
• Develop a report on the surveys and the results generated. Accuracy analysis of the results should also include in the report. The study should show the methodology applied to determine that the results are in agreement with the project’s specifications.

Aerial Triangulation

• Arrange the photographs as a continuous strip, or a block if the project includes more than one strip.
• Select and mark and draw points. Pass and tie points should mark and calculate on the paper prints.
• Mark false pass and tie points on the diapositives with a point transfer device. Points marked in stereo (tie points) should execute with utmost care.
• Measure and record pass and tie ends with a photogrammetric plotter (with digital workstations). At least an inner correction must perform before measuring pass so that image coordinates of these points can get obtained easily. Measure and mark ground control points. Ground control points get identified with the same stereo model setup.
• Compute and adjust the aerial triangulation measurements. Also check the results for possible analysis, marking, identification and control errors.
• Prepare a record of the aerial triangulation results. The record must include the photogrammetric base layout and also a diagram displaying the location and titles of all the points. The results of the computations and accuracy analysis of final adjustment concerning the project specifications should maintain in the document as well.

Stereo Compilation

The use of often CAD-based digital mapping software has analyzed the document preparation, editing and also fault checking of the stereo compilation process. The stereo compilation process is as follows:

• Select models for mapping. The selection should involve a layout of the areas for mapping from the stereo model. The operator should also instruct and focus on the limits of the stereo model for mapping.
• Fixed up the stereo models by performing interior and exterior adjustments.
• Compile the Planimetric points according to the project specifications. The specifications should also remain precise about what features are to mapped and their graphic representation concerning color, shape, symbol, and other attributes.
• Compile elevation points as contours or place elevation. Outlines should also compile according to the specified contour interval.
• Examine the map for completeness, compatibility, and also accuracy. The purpose of examining the map for completeness is to check that all the required features have mapped. Latest photogrammetric plotters have a capacity of superimposing the map on the graphic image so that both of them can inspect simultaneously with correct spatial registration. This inspection is necessary, primarily for features that are mapping from more than one stereo model.
• Edit the map and execute the required improvements.

Field Completion 

Photogrammetry can be useful for mapping only what is visible on the images. Thus, if essential features get covered by trees, human-made structures or abrupt topography, they can’t map it.

Hence, to map the missing features a field finish activity has to take place. The field completion phase of the project can use for accuracy testing of the map.

 Drafting

Drafting of photogrammetrically derived maps performs the task with CAD software. It consists the following:

• Sheet Layout
• Sheet Format
• Scale Change
• Edit and Final improvements

All of the above parameters should be part of the project specifications and should perform accordingly.

Quality Control

Here the final report on the quality and efficiency of the maps should also complete the submission of the final result. The report should examine the accuracy of the control, as described in the Ground control and also Aerial Triangulation. The procedure utilized to define the map’s spatial and also content efficiency should keep in the document as well. A statement, such as “this map matches the National Map Accuracy Standards” or “the project specifications,” is unacceptable. An actual test and analysis must complete any claim of efficiency or standard. The testing methodology applied and the decisions of its implementation must keep in the document in a final report.

Source: https://blog.nibt.education/2018/03/photogrammetry-procedure/