How do I request a topographic survey service with drones?

If what you are looking to carry out is a topographic survey, it is very important that you tell your supplier which deliverables you want and what you need them for, since depending on the size and precision you require as well as the conditions of the terrain and its vegetation it will be an optimal topographic survey with drone.

The topographic surveys can be applied to a construction or development project. To generate a topographic map in construction project you can a defined topographic survey process. In construction projects can be generated data with contour lines from topographic surveying and accurate data plus land contours in topographic maps.

When you're contemplating a topographical survey for your project can generate a boundary survey to obtain more accuracy in a topographic data. Although one of the natural features of a topographic survey is accuracy, it is good practice to perform procedures to limit the areas of existing maps.

To request a topographic survey service with drones you should consider the following factors:

• Job size
• Relative precision (submeter or metric)
• Absolute precision (georeferenced or in local system)
• Speed ​​with which you require the work (for when you require your deliverables)
• Vegetation density
• Job location
  

It should be noted that the drone is the vehicle or means that carries the sensor with which the survey is going to be carried out depending on whether it is a photogrammetry survey or a LIDAR survey, the drone is not the one that measures or performs the topographic survey.

So let's establish the pros and cons of each option.

Photogrammetric survey

• The photogrammetry survey is a result of taking photographs or Stereo pairs with a certain inclination to be able to obtain the depth from the angle from the focus.
• It is an indirect method of measurement and depends on the light since it is based on information captured by photographs
• One of the very attractive results generated by the land survey is the orthomosaic or rectified aerial photography, that is, to make the union of different photographs taken with an oblique lens in a flat projection.

Advantages

• In general the cost of the camera is cheaper than that of a LIDAR sensor
• It is ideal for areas with minimal vegetation
• Serves to cover large areas
• It is a cheaper system to measure mounds since they generally do not have vegetation
• The Orthomosaic gives the user great contextual information

Disadvantages

• As it is an indirect measurement method, it is not recommended in areas with vegetation.
• In general, its precision in Z is less than his LIDAR
• It lacks an Intensity value that facilitates better information filtering.

LIDAR topographic survey

Also known as LIDAR flight, it is the result of mounting a LIDAR sensor on a drone.

The LIDAR system is mainly made up of the following components:

• LIDAR sensor is the one that generates the laser beams that bounce off the natural terrain.
• IMU is the inertial motion system that measures the variations in the three axes.
• GNSS is the global positioning system that allows to know the location of the system on the earth.
• Photographic camera in case you want to add color to the points.
• The LIDAR system is a direct measurement method and depending on the sensor allows measurements in areas of dense vegetation

Advantages

• The LIDAR system can traverse the vegetation allowing natural terrain surveys to be carried out in areas where photogrammetry cannot, such as jungles and forests.
• Serves to cover large areas.
• Information discrimination is more accurate as it has a more intense variable in addition to the color and coordinate variables.
• Because it is a direct measurement system, it is more accurate in Z.
• It gives us the exact value of the natural terrain.

Disadvantages

• It is more expensive
• Not ideal for generating an orthomosaic during LiDAR data acquisition

In general, the two systems never have a great added value when it comes to measuring large areas and when they are mounted on a drone they have a cost-benefit limitation up to an approximate size of 3500 ha where they already begin to compete with manned flights both for photogrammetry studies as for LIDAR flights.

For both cases, the requested deliverables are usually:

• Level Curves
• Shaft sections and profiles
• Digital Terrain Model
• Point cloud

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