IN THIS ARTICLE
Introduction to processing options
Weather conditions during capture
Limit orthomosaic size
Rig relatives calibration tool
Radiometric correction in PIX4Dfields
PIX4Dfields is intended for fast and accurate photogrammetric processing of aerial agricultural imagery. This article describes the Processing options for generating orthomosaics. These features are accessible after images have been imported and before the start of processing.
Processing options menu.
Fast Processing is the default processing option as it gives rapid results with minimal compromise in the accuracy of outputs. Fast processing has had several improvements over the years such as GPU acceleration, RTK positioning, rig relatives calibration tool, and radiometric improvements. Fast processing still offers the best option for generating an orthomosaic, index maps, and DSM with sufficient resolution for most farming applications.
Accurate processing was introduced in PIX4Dfields 1.11. This option generates a highly detailed height model along with a more accurate orthomosaic. However, the more complex processing algorithm will increase processing times. This is ideal for trial plots, spot application, and terrain analysis.
Weather and sun are significant factors that influence multispectral imagery. Cloud cover and solar position should be accounted for in order to minimize the effect of measurement errors caused by changes in ambient light. PIX4Dfields allows specifying Weather conditions during capture with either overcast or clear sky options. In addition, if the camera is equipped with a sunshine sensor a sun angle correction will be performed under any weather conditions.
The file size of the orthomosaic can be predetermined by either defining the Ground Sample Distance (GSD) and/or the Maximum total megapixels:
- The GSD is the length of a pixel in distance units (usually cm or inches) as measured on the ground. A smaller GSD implies a higher resolution with more pixels and more detail. However, the increase in pixels will also result in a larger file size. Conversely, a larger GSD will result in a lower resolution and smaller file size.
- The Maximum total megapixels refers to the maximum size in pixels of the GeoTIFF. The default setting is 50MP. However, this should be unchecked in order to achieve maximum resolution.
A detailed guide is provided in Orthomosaic GSD.
Advanced settings was introduced in PIX4Dfields 1.11, and gives additional options for processing depending on the type of dataset. Rig relative calibration and Radiometric correction are available for multispectral imagery. Full blending and GPU acceleration are available for RGB imagery.
Advanced settings menu.
Full blending can improve color transitions and reduce "honeycomb" effects. When enabled the GPU acceleration is automatically disabled.
Rig relative calibration reduces the "rainbow" effect caused by misaligned color bands. This option will be automatically enabled for cameras that have multiple sensors, such as the Parrot Sequoia or the MicaSense RedEdge-P. A detailed guide is provided in rig relatives calibration tool.
Radiometric correction is required to be able to compare images taken at different points in time under different weather conditions. A radiometric correction is required in order to compute reliable index values. PIX4Dfields comes equipped with our latest radiometry module which calibrates multispectral images, and includes support for automatic detection of reflectance targets. A detailed guide is provided in radiometric correction.
GPU acceleration utilizes a computer's GPU to reduce processing times for RGB imagery. This option is not available for multispectral imagery. If the GPU acceleration is enabled, the most suitable GPU is automatically selected (independent of the settings in the operating system). If the GPU acceleration is disabled, processing will default to the CPU.
See the table below for a comparison of processing times for RGB imagery: