A model for environmental data extraction from multimedia and its evaluation against various chemical weather forecasting datasets

•Semi-automatic extraction of air quality and pollen data from heatmaps.•Integration of OCR and image processing for environmental data extraction.•Development of an annotation tool for template-based configuration of heatmaps.•Evaluation of environmental data extraction from heatmaps against real forecasts.

Environmental data analysis and information provision are considered of great importance for people, since environmental conditions are strongly related to health issues and directly affect a variety of everyday activities. Nowadays, there are several free web-based services that provide environmental information in several formats with map images being the most commonly used to present air quality and pollen forecasts. This format, despite being intuitive for humans, complicates the extraction and processing of the underlying data. Typical examples of this case are the chemical weather forecasts, which are usually encoded heatmaps (i.e. graphical representation of matrix data with colors), while the forecasted numerical pollutant concentrations are commonly unavailable. This work presents a model for the semi-automatic extraction of such information based on a template configuration tool, on methodologies for data reconstruction from images, as well as on text processing and Optical Character Recognition (OCR). The aforementioned modules are integrated in a standalone framework, which is extensively evaluated by comparing data extracted from a variety of chemical weather heat maps against the real numerical values produced by chemical weather forecasting models. The results demonstrate a satisfactory performance in terms of data recovery and positional accuracy.