Working in the UAV world isn’t always about the drone. In fact, the drone is only one piece of a single stage of an accurate high resolution mapping workflow. This blog will outline various stages of the GEO Jobe UAV process. It will then highlight one example of the final stages by focusing on extracting and identifying features derived from the data. Because it is the data from drone missions and all that can be done with them that truly have value – not the drone.
Most commercial grade drones these days capture geocoded images during their mapping missions. The GPS on drones have become quite accurate; most are equipped with IMUs to correct for the pitch, roll, and yaw of the drone, and flight applications require the highest degree of ground accuracy through some sort of geolocation correction. Setting ground control points and capturing their locations with high accuracy GPS units for use in the photogrammetric processing is one technique to improve accuracy. Correcting the image coordinates through other techniques, including real time kinematics (RTK) or post processing kinematics (PPK), are becoming more and more popular. Many end-use cases in the Architecture Engineering and Construction (AEC) industry rely on and require geographically accurate mapping products for grading, building, and delivering as-built drawings.
Drones make the data capture process much faster and safer than traditional methods. But being able to take and make measurements from the processed products is what creates the most value. There are several derived products available from the drone data. AEC professionals use topographic surfaces, planimetric features, and 3D point clouds for design, planning, and construction. In the survey arena, two very important by products of the drone workflow are digital terrain models for topographic modelling, i.e. contours, and hardscape physical features on the ground like pavement, curbs, sidewalks, culverts, headwalls, and stormwater intakes.
There are many ways and applications that combine the digital surface model and ortho to create virtual field shots to create a TIN.
Once the TIN is built, contours can be created. In order to extract hard visible features on a site from aerial imagery, one needs to locate and identify them. The remainder of this blog will be a quick study in using one product, Pix4DSurvey, for accurately extracting physical linework on a site depicted by aerial imagery.
The imagery in an ortho has none of the mathematical properties that end users need in order to calculate length, height, or volume, for example. The ortho is a raster image. What designers need is data in vector format. The data must have geographic or locational attributes associated with them. Pix4DSurvey allows users to create vector data from the raster images. Any CAD or GIS system can use the ortho as a base map to create features by tracing over features on the ortho. We choose to use the Pix application because of the increased accuracy it is capable of producing. That is what I intend to illustrate in this Blog.
Using just the ortho as a base and tracing from it in CAD or GIS can create a vector dataset. The ortho however is a compilation of all of the photos that captured a specific spot or location. The ortho then takes information from all those photos to accurately represent that spot. The ortho does not have the same resolution as the individual images. Drawing features from the ortho becomes an approximation.
The resolution of each image is much higher than the mosaic ortho. Using individual images to identify and capture features is a far more accurate representation because the feature’s location is based on higher resolution imagery.
As always the emphasis is on resolution in the aerial imagery field. So for feature extraction, use the highest resolution at your disposal and capture from the images and not the ortho. GEO Jobe UAV clients expect accurate high resolution digital mapping products. Our goal is to meet if not exceed those expectations.