THIS REPORT is a personal account of the ISPRS Hannover Workshop, held at the Institute for Photogrammetry and GeoInformation (IPI) at Leibniz Universit€ at Hannover (or Hanover, if you prefer the rather unnecessary English spelling) in June 2017. The workshop was a joint meeting of: High-Resolution Earth Imaging for Geospatial Information (HRIGI17); City Models, Roads and Traffic (CMRT17); Image Sequence Analysis (ISA17); and the European Calibration and Orientation Workshop (EuroCOW). That is a rather difficult list to remember, so everyone refers to it simply as the Hannover Workshop (although this proved difficult last time round in 2015, when it was held in Munich).
TopicsAs this was a meeting of several different sub-groups, the topics varied across multiple disciplines, from sensor calibration of aerial cameras to the identification of windows in building fac ßades. A total of 40 oral presentations were made, in sessions loosely themed to match the topics of the sub-groups involved in the workshop. One of the nice things about this workshop, compared to the much larger ISPRS Congress, is that there are no parallel sessionsif you wanted to attend a particular talk, you could do so without fearing that you would miss anything important in another session. The organisers reported that 209 people attended the workshop, from a total of 31 countries. Although the majority of people were from Europe there was a significant contingent from further afield, including Australia, Canada, USA and Iran.
SensorsIn previous Hannover Workshops, satellite imagery and new satellite sensors have been significant subjects of discussion. This time the emphasis was more on airborne and terrestrial sensors: platforms including conventional aircraft, unmanned aerial vehicles (UAVs) and road vehicles. There was also work on the extraction of data from CCTV and fixed-position cameras, for surveillance and counterterrorist activities.Conventional aerial cameras, taking images from a nadir perspective, are now so prevalent that few people mention them at meetings such as this one. There is much more interest in newer technologies, especially oblique camera systems such as the Vexcel Osprey Prime, the IGI Urban Mapper and the Leica City Mapper. Vexcel and IGI have designed their systems to be, effectively, a conventional large field-of-view nadir camera surrounded by four oblique cameras pointing fore, aft, left and right. The exact degree of offset of the oblique cameras was a subject of debate, with 45°being the usual angle, but not everyone agreeing that it was the best. Another difference between the systems is the relative pixel size (ground sample distance (GSD)) between the nadir and the oblique sensors (measured at the centre of the frame). The IGI oblique cameras have a central GSD of 1Á4 times the