If you have not done so already check out our Guidelines of a Quality Orthomosaic article that will cover some of the basic rules for producing 2 Dimension maps. All of the topics mentioned in that article apply to collecting data for 3D outputs.


Planning a survey for the purposes of 3 Dimensional outputs will change the basic workflow of how you capture the field. In order to build 3 Dimensional features from aerial imagery, more redundancy is needed across your source imagery. To find a precise vertical measure of a building or other feature in your survey it is necessary to capture this feature from several different angles. This allows the software to triangulate that feature and come up with a accurate Vertical value for the 3D outputs. Below we will discuss the various flight methods that you can use to ensure quality 3D measurements in your final products. 



What are 3D outputs? 

3 Dimensional outputs are any product supplied by PrecisionMapper that contains some vertical measurement of the subject matter below. Below are the PrecisionMapper output files that have a 3 Dimensional measurements included. If you are specifically interested in any of these output files be sure to follow the flight processes noted further along in this article. 

  • Digital Surface Model (DSM)

  • Triangle Mesh

  • Point Cloud

  • 3D Model

  • Contours

  • DXF


Vertical measurements in our 3D outputs are represented in terms of Relative elevation and not Absolute above Mean Sea Level elevation. This means that elevation measurements are relative to the takeoff location of the drone, here the elevation is set as 0 meters and all elevation values in the survey are relative to this. 




Flying your Grid

The first step in collecting your source data is to plan a grid flight plan over your area of interest. A grid flight is a simple lawn mower path across your survey area at a constant altitude. Throughout the flight nadir images are collected, this means that the sensor is looking directly down on the ground when capturing images.To plan accordingly for this part of your flight be sure to check out our Guidelines of a Quality Orthomosaic article. One thing that will differ between a Grid flight for 2D outputs and a Grid flight for 3D outputs is the overlap values that you will use. Below you will find recommended flight altitudes and overlap values specific to the collection of 3 Dimensional outputs.


Recommended Flight Altitude and Overlap for 3D outputs- Grid Flight


Zenmuse x3
80 m
85% Forward 80% Side
Zenmuse x4s
50 m
85% Forward 80% Side
Zenmuse x5 15mm
75 m
85% Forward 75% Side
Zenmuse x5s 15mm
75 m
85% Forward 75% Side
Zenmuse XT

3D outputs unavailable for Thermal Imagery 


Phantom 4 Pro
50 m
85% Forward 80% Side
Sequoia
50 m
85% Forward 80% Side

                                


Flying your Orbits

Following the grid flight over your area of interest you should also fly an orbital pattern around the main feature you are interested in mapping in 3 Dimensions. During the orbital pattern Oblique images are captured, this means that they camera angle is looking in on the ground at a angle as opposed to Nadir imagery looking directly at the ground. Atleast one orbit is necessary in producing a good output, multiple orbits may be considered for further redundancy and more detail on the side walls of the 3D feature. For full detail on the flight process for Orbital flights check out our Orbital Flight Modes article of the knowledge base. 


Below are some of the main rules you should be familiar with to produce a successful 3D product from orbital flights. 

  • Be sure to set the camera angle for your orbit so that the horizon or sky line is not captured in the image. This has been known to cause issues in the stitching of your data. 

  • To pickup details in your 3D model for overhanging features like the edge of a roof orbits should be flown at lower altitudes and a shallower angle.

  • Make sure to capture the orbital pattern after your Grid flight. There is no need to clear your camera card between these flights. Let them build on one SD card and treat them as a single upload to PrecisionMapper.