## 2 Materials and Methods  
### System's Design and Construction  
A low-cost, 1-DOF linear robotic camera system, named RoboPlantDect, targeting the systematic image acquisition of plants and facilitating future research endeavors like greenhouse growth plant monitoring procedures, was fully designed and constructed from scratch (Figure 1a-h). The initial idea originated from the need for an automated plant photography system for lettuce cultivation research purposes in our university's facilities, without having to sacrifice many human resources for field observations. The original purpose was to monitor, from above, lettuce seedlings, at the stage of four true leaves, growing in plastic pots and arranged in a single row inside an unheated saddle roof double-span greenhouse covered with polyethylene film. However, except from the thorough inspection and consideration of the usual design factors like the cost and the availability of the construction materials, the ease of assembly, and the maintenance costs, a few more prerequisites were defined early in the design process phase. More specifically, among others, these included the following:  
* The system should be able to automatically detect and accurately localize the spaced plants that are growing apart in plastic pots, positioned in a fully randomized design, in a 3 m long row;
* The system as a whole, should be lightweight and portable but also easily scalable if needed in order to facilitate its easy positioning for monitoring other rows inside the greenhouse too;
* To ensure that the linear robotic camera system can precisely reach each of the target plants, the actuator must exhibit sufficient precision in its movement. Upon reaching the target, the system should capture a high-resolution, color, top-view image with the plant ideally centered;
* With none or minor modifications and/or software adjustment settings, the linear robotic camera system could also be applicable for other plant species' monitoring research and investigation purposes in hydroponic systems (e.g., spinach, sweet peppers, herbs, and strawberries, to name a few);
* The system should not, in any manner, obstruct the plants' growth;
* Detected and localized plant images along with all the plant growth-related data measurements performed, together with the datalogging information, should be automatically stored locally, but also transmitted to a remote location and synched in a secure and transparent manner;
* No human intervention should be necessary at any stage of plant detection and monitoring. The implementation of the computer vision-guided system is divided into two parts, and more specifically, into the following: (a) the system's design and construction, which describe and present the hardware parts and the implementation details that comprise the whole system assembly and (b) the system's software programming and workflow, which describes the system's software building blocks and the complete pipeline. The detailed, full list of materials and parts that were designed, constructed, assembled, or purchased, is presented in Table 1 of Appendix A. In Figure 2, a simplified schematic diagram shows the complete system's pipeline. Figure 1: View and details of the constructed RoboplantDect 1-DOF linear robotic camera system. (**a**) Global system of coordinates, applied to the robotic camera system. Transformations and measurements involving the various coordinate systems of interest are performed in reference to this coordinate system, which belongs to the “right side” of the device. The camera is moving in the X-axis only.