Tim Pruss UAS Blog

Introduction In this lab I integrate GCPs into the Pix4D process. This lab is very similar to the previous with the main difference being the addition of GCPs along with the extra steps that entails. GCPs or Ground Control Points are points of known coordinates in the area of interest. GCPs are essentially required when the absolute accuracy (position of the area of interest on the earth) of a project is important although this requirement can be waived if the images have geolocation. Images with geolocation utilize GPS data to record the position of an image when it is taken. Due to the innate inaccuracy of GPS, additional use of GCPs along with image geolocation can reduce the shift of the area from meters to centimeters. GCPs have an absolute minimum number requirement of 3 to be taken into account with each being present in at least 2 images. The recommended number is between 5-10 with additional GCPs having diminishing returns, even in large projects. If there are more GCPs th

Intro to the Pix4D software In this lab we used the Pix4D software to construct a point cloud data set, true orthomosaic, and a digital surface model without the use of GCPs. What is Pix4D? Pix4D is a very popular software company that is primarily known for it’s software products that utilize photogrammetry and computer vision algorithms to transform pictures (whether RGB, thermal, multispectral, or otherwise) into 3D maps and models. The software is easy to use and has many versatile features. What products does it generate? The program that we used, the “Pix4Dmapper”, can generate point clouds, orthomosaics, digital surface models, 3D textured meshes, contour line maps, reflectance maps, index maps, and thermal maps depending on what kind of data you input and what kinds of sensors you used. Why is it so integral to UAS data processing? Without Pix4Dmapper (or at least a functionally similar program) we would have no way of processing our UAS images and the images would be

Introduction What is photogrammetry? Photogrammetry, as stated in the ArcPro documentation, is "the science of obtaining reliable measurements from photographs and digital imagery." Aerial photogrammetry and close-range photogrammetry are the two types. We will primarily be working with aerial-photogrammetry which utilizes several overlapping photos taken from the air and pointed straight down.  What types of distortion does remotely sensed imagery have in its raw form? Before being processed, the raw imagery is distorted by multiple types of distortion.  Perspective distortion is caused by the fact that each image has it's own unique perspective geometry, which is to say that an object will look different depending on what angle you look at it from and with what kind of sensor.  Field of View distortion is dependent on the focal length, lens, and altitude of the sensor. The focal length is the distance between the lens rear nodal point and the focal plane. The