A method for determining a height of an object or object's subparts above a horizontal plane from a single image recorded by an imaging device comprised by an aerial vehicle, wherein the imaging device is configured to record an image in an image space from an object space, the method comprising the steps of: - Flying with the aerial vehicle above the horizontal plane, - Recording a single image with the imaging device, wherein the object is comprised by the image, - Acquiring imaging device parameters, wherein the imaging device parameters comprise information on an orientation (θx, θy, θz) of the imaging device in relation to a world coordinate system and a focal length (f) as well as an information comprising the pixel pitch of the imaging device, - Determining an information on the elevation of the imaging device above at least one point of contact at which the object is in contact with the horizontal plane in the object space, - Determining the height of the object or the object's subpart above the horizontal plane in the object space by means of a projection model that relates coordinates in the object space with coordinates in the image space using the recorded image, the imaging device parameters and the information on the elevation of imaging device, characterized in that the method further comprises the step of: - Recording in the image a ruler object in the object space, wherein the ruler object has a known extent along at least one direction in the horizontal plane in the object space, wherein the elevation of the imaging device is determined from the imaging device parameters and the extent of the ruler object in the horizontal plane. - Flying with the aerial vehicle above the horizontal plane, - Recording a single image with the imaging device, wherein the object is comprised by the image, - Acquiring imaging device parameters, wherein the imaging device parameters comprise information on an orientation (θx, θy, θz) of the imaging device in relation to a world coordinate system and a focal length (f) as well as an information comprising the pixel pitch of the imaging device, - Determining an information on the elevation of the imaging device above at least one point of contact at which the object is in contact with the horizontal plane in the object space, - Determining the height of the object or the object's subpart above the horizontal plane in the object space by means of a projection model that relates coordinates in the object space with coordinates in the image space using the recorded image, the imaging device parameters and the information on the elevation of imaging device, characterized in that the method further comprises the step of: - Recording in the image a ruler object in the object space, wherein the ruler object has a known extent along at least one direction in the horizontal plane in the object space, wherein the elevation of the imaging device is determined from the imaging device parameters and the extent of the ruler object in the horizontal plane. - Recording in the image a ruler object in the object space, wherein the ruler object has a known extent along at least one direction in the horizontal plane in the object space, wherein the elevation of the imaging device is determined from the imaging device parameters and the extent of the ruler object in the horizontal plane.