The most important advantage of widefield cameras is, precisely, the "widefield", since this offers the observers the possibility of obtaining vast amounts of data in a much shorter observing time. However, for a reliable data interpretation, it is necessary a proper data calibration. Concerning the flatfielding of images, many times it is required to obtain several integrations in blank regions (sky patches without bright sources) nearby to the science target areas. TESELA is a service developed to provide access to a catalogue of blank regions, based on the application of the Delaunay triangulation of the sky. The present implementation of TESELA uses as source for the star coordinates the Tycho-2 Catalogue (Hog et al. 2000). The system has been jointly developed by the Department of Astrophysics of the Universidad Complutense de Madrid and CAB (INTA-CSIC) and is maintained at CAB (INTA-CSIC). If you use TESELA in your research, please include the following acknowledgement in any resulting publications: "This publication makes use of TESELA, developed under the Spanish Virtual Observatory project supported from the Spanish MICINN through grant AyA2008-02156." "Partially funded by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD2006-00070: First Science with the GTC"
