Start by setting the boundary of your project. This is dependent on the terrain and size of the mapping project. What is most important before flying to collect data is remembering that your flight boundary must be set beyond that of your project.
We recommend you set the flight boundary at least 100 feet beyond your selected processing boundary to ensure you have an adequate artifact distortion buffer. This will also ensure the geospatial integrity of the model.
If flight includes the use of LiDAR sensors, flight boundary should include 1/2 swath distance.
The flight grid that you select for your data collection stage will vary greatly depending on the profile of the site you are flying, and things like vegetation density and structures or buildings will affect the camera settings required for accurate data collection.
All projects should be collected at 90 degrees/nadir for the main grid. You can add extra passes with 45-60 degree obliques to make the buildings & vertical structures look better in a 3D model but it doesn’t apply to the work AirWorks is doing nor will it provide the data quality we need to provide an accurate CAD deliverable. A double grid with perpendicular flight lines is recommended for all LiDAR collections.
|Site Profile||Recommended Camera Angle||Recommended Flight Grid|
|Dense, urban setting with many vertical structures||60 degrees, oblique||Double Grid|
|Dense, urban setting without vertical structures||90 degrees||Single or Double Grid|
|Suburban setting with vegetation||90 degrees, oblique and nadir||Single or Double Grid|
|Rural, open setting without vegetation||90 degrees, nadir||Single Grid|
|Homogenous areas (ex: snowcapped fields, woods or forests, large bodies of water, etc.)||In this case, it is best to increase flight altitude in order to add more differentiated details in the images you collect, which will also make data processing and photogrammetry|
The altitude of your flight will depend on the type of aircraft you select, and the sensor quality it possesses. In general, for aerial imagery, we recommend a flight altitude of 150 ft along with a 20-megapixel camera resolution and 0.5-inch ground sampling distance (GSD). For aerial LiDAR, it is dependent on the number of returns and beam divergence. If your sensor has multiple returns and low beam divergence, you can fly around 250-300′ and collect a point cloud with low noise/distortion and a high level of detail; as you have fewer returns or more beam divergence over a shorter distance, you need to reduce flight altitude to be closer to 150′.
That being said, your flight altitude can be higher or lower depending on the accuracy requirements of your specific project. Accuracy is also dependent on the number and distribution of ground control points, the control collection methods, and processing techniques.
Size of Flight
Number of Images
The biggest factor in deciding the number of images you should collect during your flight will depend on your choice of photogrammetry software, as each one will have different requirements, as well as limits. A general rule of thumb to follow is to not try to process projects with more than 5,000 images per flight, but collecting more images will always render better results than attempting to process small datasets with limited images.
If you do have a flight with more than 5000 images, we recommend breaking up the project into multiple flights and processing them as separate datasets during the photogrammetry stage, then combining them into one single dataset in post-processing.
Point Cloud Density
If you have a point cloud that is over 3 GB in size, we recommend breaking up the project into multiple las files. If you have a flight with a point cloud density greater than 5000 points per square meter (ppsm), we recommend thinning the point cloud to reduce the density of points.