The present invention relates to providing a projection data for providing a guidance image. In order to provide an enhanced guiding image technique for generating a guidance image of the patient's anatomy to be projected on the body surface of the patient, such that a at least a basis for a corrected guidance image for a better correlation to the patient's current motion can be provided, in particular to the patient's current breathing motion state, a device (10) for providing a projection data set is provided that comprises a storage means (12), an input interface (14), a processing unit (16) and an output interface (18). The storage means is configured to store a pre-determined basis data set representing a 3D tomographic image of a subject (20). The input interface is configured to receive reference data representing a current spatial depiction at least of a target region (22) of the subject. The processing unit is configured to register the reference data on the pre-determined basis data set. The processing unit is further configured to transform, based on the reference data and the result of the registration, the pre-determined basis data set resulting in a working data set representing a transformed 3D tomographic image indicating the current spatial anatomy relation at least for the target region of the subject. The processing unit is also configured to segment the working data set resulting in a projection data set representing the target region of the subject. Still further, output interface is configured to provide the projection data set for a further purpose.