A computer program comprising computer instructions which, when loaded in a processor, cause the processor to operate a system for providing visual information about a location of a tumour under a body surface of a human or animal body, to: interact, by a tumour sensor tracking system, with at least one electromagnetic tumour sensor to determine an individual location of the tumour sensor in space; determine a digital volumetric tumour model representative of the tumour using information obtained from an imaging process; map each tumour sensor location to the tumour model; interact, by a surgical tool sensor tracking system, with at least one surgical tool sensor of a surgical tool to determine an individual location of the surgical tool sensor in space, wherein the surgical tool sensor tracking system is calibrated to provide locations in a first coordinate system, and wherein the tumour sensor tracking system is calibrated to provide locations in a second coordinate system; determining a digital surgical tool model representative of the surgical tool; map each surgical tool sensor location to the surgical tool model; receiving information, obtained by scanning the human or animal body, about at least one anatomical structure in the human or animal body in a vicinity of the tumour; interact, by a reference sensor tracking system, with at least one reference sensor located on a surface of the human or animal body to determine an individual location of the reference sensor in space, wherein the reference sensor tracking system is calibrated to provide locations in a third coordinate system; map each reference sensor location to the at least one anatomical structure in the scanned human or animal body; determine the location of each tumour sensor in space; determine the location of each surgical tool sensor in space; determine the location of each reference sensor in space; assemble, based on the first and second coordinate systems, a virtual image showing the tumour model, as located with the at least one tumour sensor, in a spatial relationship to the surgical tool model, as located with the at least one surgical tool sensor, wherein the first, second, and third coordinate systems are all the same or are registered to each other; assemble, based on the third coordinate system, the virtual image further to show the at least one anatomical structure, as located with the at least one reference sensor, in a spatial relationship to the tumour model, as located with the at least one tumour sensor, and in a spatial relationship to the surgical tool model, as located with the at least one surgical tool sensor; and display, by a displaying component, the virtual image on a display device. interact, by a tumour sensor tracking system, with at least one electromagnetic tumour sensor to determine an individual location of the tumour sensor in space; determine a digital volumetric tumour model representative of the tumour using information obtained from an imaging process; map each tumour sensor location to the tumour model; interact, by a surgical tool sensor tracking system, with at least one surgical tool sensor of a surgical tool to determine an individual location of the surgical tool sensor in space, wherein the surgical tool sensor tracking system is calibrated to provide locations in a first coordinate system, and wherein the tumour sensor tracking system is calibrated to provide locations in a second coordinate system; determining a digital surgical tool model representative of the surgical tool; map each surgical tool sensor location to the surgical tool model; receiving information, obtained by scanning the human or animal body, about at least one anatomical structure in the human or animal body in a vicinity of the tumour; interact, by a reference sensor tracking system, with at least one reference sensor located on a surface of the human or animal body to determine an individual location of the reference sensor in space, wherein the reference sensor tracking system is calibrated to provide locations in a third coordinate system; map each reference sensor location to the at least one anatomical structure in the scanned human or animal body; determine the location of each tumour sensor in space; determine the location of each surgical tool sensor in space; determine the location of each reference sensor in space; assemble, based on the first and second coordinate systems, a virtual image showing the tumour model, as located with the at least one tumour sensor, in a spatial relationship to the surgical tool model, as located with the at least one surgical tool sensor, wherein the first, second, and third coordinate systems are all the same or are registered to each other; assemble, based on the third coordinate system, the virtual image further to show the at least one anatomical structure, as located with the at least one reference sensor, in a spatial relationship to the tumour model, as located with the at least one tumour sensor, and in a spatial relationship to the surgical tool model, as located with the at least one surgical tool sensor; and display, by a displaying component, the virtual image on a display device.