Vertical Aerial Photographs

From OpenStreetMap Wiki
Jump to: navigation, search
Available languages
Deutsch English

Vertical aerial photographs are valuable sources of data for OpenStreetMap. While surveying by collecting GPS tracks is the primary way for collecting data, tracing features from an overhead photograph makes inputting vast amounts of data quicker to be filled in and verified later via on-the-ground surveying. A couple of prominent examples of OSM data initiated via tracing from photos are the Gaza Strip and Baghdad.

These photographs are usually taken from satellites. Companies like DigitalGlobe and GeoEye and U.S. Government projects like Landsat provide satellite imagery for free or for a licensing fee.

Aerial photographs can also be obtained from airplanes equipped with cameras or even balloons, or even any airborne device fitted with a camera.

Sources already in use

See Aerial Imagery for a directory of sources that can be readily used in OSM editors.

Bing

Bing (Microsoft) gave us special permission to use their imagery to create our maps. This happened relatively recently (November 2010). It is supported in Potlatch 2 and JOSM. See the Bing page for details.

Possible sources

No copyright

http://www.gesource.ac.uk/worldguide/satellite.html

OpenAerialMap

Project dormant but proposed for revival. Check their wiki at wiki.openaerialmap.org/OpenStreetMap

Organisation / Heritage / History

Sources that are governmental, historical or otherwise assumed not for profit.

The interface is easy, but you may be confused because there's no actual photos online - it's just a catalogue of the photos, which then have to be bought from the University. They started taking photos in 1947, so I assume some are out of copyright by now. They're also mostly of open countryside, and have a restricted field of view, as far as I can tell, so may not be much use anyway.
The interface has been replaced with a new slippy map viewer (and an OSM background) using code cloned from CycleStreets! Photographs not viewable on the site - see the info page for updates. - Martin (I work at Geography)

USGS

Costs money

Homebrew

There are many documented examples of homebrew vertical aerial photography using Balloons, Kites, UAVs etc. This potentially offers an approach for obtaining open licensed imagery cheaply and on-demand in particular area. Typically it's fairly easy to get very high resolution imagery, but difficult to cover a significant area, due to the limited height.

The limits can be both of technical and legal nature. There are legal restrictions on flight altitude which differ per country and within countries are most strict over big cities. Flights of every kind of airship (including kite) are additionally restricted in proximity of airports. It is important to know the local airspace regulations relevant to a given kind of airship. In the light of law balloons, kites, model aircraft and UAVs are each a separate category and different restrictions may apply. It is often possible to obtain a permit to make a given flight from an airspace controlling body but request may need to be submitted with advance. In some situations it is a good idea to notify the body even if a permit is not strictly required.

Open-source software for rectification (not so much for georeferencing) of the imagery is scarce, some work is ongoing. Georeferencing is an easier task and can be done with programs such as QuantumGIS or the Map Warper website using the GDAL library, including some basic deformations of the images. Quality rectification of imagery is more difficult however because it needs software that can understand the camera optics. It is also possible to rectify an image using just a huge number of control points in programs like QGIS or a simple graphics editor (Gimp, Photoshop) but it is very time consuming and results can leave a lot to be desired. Additionally the area must either be very well mapped or reference imagery must be available for adding control points. Some possibile solutions are: (links needed)

  • Hugin (See HOWTO) - primarily a panorama stitching program with advanced optics, can be used for quite precise rectification
  • Mapknitter - easy to use, a lot of information available on the site including a video tutorial (best suitable for almost-vertical images made with rectilinear lenses)
  • potentially useful: ILWIS, OSSIM - professional and quite heavy GIS / Remote Sensing suites that originally were closed-source but have become Free Software later. ILWIS, while opensource, is Windows-only. OSSIM is built on the Octopus library that seems to have been co-developed by the French government.

Balloons

The Public laboratory for Open Technology and Science maintains a series of kits and how-tos on balloon and kite mapping techniques, as well as the browser-based Mapknitter for stitching over satellite imagery. Mapknitter synchs with Open Aerial Map to enable easy OSM tracing.

Kites

OSMer User:Balrog has been experimenting with kite mapping

User:Balrog's kite Osmcopter-split-screen.jpg

He has managed to create some tiled rectified imagery using a process involving Hugin: http://ooc.openstreetmap.pl/kap-warsaw.xhtml (firefox)

User:Mikel has a funny video somewhere of crashing a kite in Palestine. link?

DIY kite mapping on the UCL blog

Others


Summary: Kite equipment may be a little more expensive than hand-made balloon, but helium is not used up such as with helium balloons which need to be refilled often. Transportation is also easy because the "Sutton flowform"-type kites are fully foldable to small size packets (laptop size). "Sled" kites (PowerSled and similar) can also be used. They normally have a plastic frame but can also be flown without the frame. As with balloons, weather conditions are also very important and it may be impossible to make a flight in one location for long periods of time. In cities considerable space is needed for a start so it may be impossible to photograph some densely built-up areas at a good angle.

Model aircraft

The bigger RC helicopter and airplane models can provide enough lift to lift a quality compact camera (100 - 150g) without problems, and some can lift a SLR camera. Reaching useful altitudes (500m - 1000m) may be difficult with standard radio control due to high levels of interference in the cities, and battery life.

Model airplanes have the disadvantage of requiring some space for landing. They can possibly cover bigger areas than RC helicopters because very little battery power is used for horizontal movement if the model has a good gliding ratio. Julio Costa from the Chile OSM community has been experimenting with an RC airplane, seemingly without much success yet (flickr stream link). RC airplanes are probably cheaper to use than quadcopters because of mass production. Some of the cheaper models capable of lifting a 150g camera cost EUR150 to EUR200 in Europe.

RC helicopters should be much better adapted to city environment and are still a little cheaper than quadcopters. They are however difficult to steer and need a lot of training before a successful flight (not followed by costly repairs). The cheaper 6-channel models (such as the E-sky Belt CP series) capable of lifting a compact camera are EUR150 to EUR200 in Europe. RC helicopters are very sensitive to added start weight and control is even more difficult with the camera attached. There are reports of someone lifting over 1.3kg with a Belt CP helicopter (but it became almost uncontrollable). 3-channel RC helicopters of the same size are much cheaper (EUR50 to EUR100) but it's not confirmed that they can be used for lifting a 150g camera. User:Balrog is experimenting with some 6-channel E-sky helicopters.

Quadcopters

The OSMers behind OpenStreetPhoto were developing a quadcopter (2009). Currently the blog seems to indicate they decided on a ritewing RC airplane instead, blog is in Dutch though.

According to their wiki, their max. budget for a single quadcopter unit was EURO2500. As quadcopters come into more mass-production they will be becoming cheaper, similarly to RC models of helicopters and planes, which are currently much cheaper despite sometimes higher level of complexity. There are already companies building toy or just-a-little-too-big-for-a-toy quadcopters, operating since 2010. For example the Gaui 330 is an interesting model. Though definitely too small to lift a SLR camera, it can possibly lift a compact hi-res Canon (some 14MP models weight in the range of just 130 grams). They are already much cheaper (EUR299 basic model) than microcopter.de self-made quadcopters or the commercial aerial-imagery platform offerings.

Quadcopters may have the same problems with battery life as model aircraft.

They can however fly autonomously if programmed before the flight so the radio range may be less of a problem. Due to the possibility of autonomous flight a quadcopter counts as an UAV and not a model aircraft in some jurisdictions (at least in Poland) and may in theory require airworthiness certification in controlled airspace, unlike model aircraft.

Unmanned gliders

Outside of UK

Africa

Australia

Austria

France

  • Brest métropole océane This is covered by the by-nc-sa creative commons license.
  • Raw aerial photos by IGN which can be downloaded here are under the licence "public information that is freely reusable". ATTENTION this is very different from the orthophoto which is visible in Géoportail: that one is not free and under copyright. The difference is the georeferencing: the raw aerial photos must be rotated and displaced to fit with existing data, whereas the orthophoto is ready to use.

Germany

A list of WMS-sources and links for integration JOSM and potlatch can be found here:[3] and here WikiProject_Germany/Luftbilder

Italy

The national portal of cartography, operated by the ministry for environment, offers good aerial imagery to trace from covering the whole country (2006) and newer ones for the regions of Lazio and Umbria (2008). More information in Italian here: WikiProject_Italy/PCN. The links to enter in JOSM are:

  • 2006, all of Italy:
http://wms.pcn.minambiente.it/cgi-bin/mapserv.exe?map=/ms_ogc/service/ortofoto_colore_06.map&LAYERS=ortofoto_colore_06_32,ortofoto_colore_06_33&REQUEST=GetMap&VERSION=1.1.1&FORMAT=image%2Fjpeg&FORMAT=image%2Fpng&
  • 2008, Lazio and Umbria:
http://wms.pcn.minambiente.it/cgi-bin/mapserv.exe?map=/ms_ogc/service/ortofoto_colore_08.map&LAYERS=ortofoto_colore&REQUEST=GetMap&VERSION=1.1.1&FORMAT=image%2Fpng&

Glossary

Oblique 
Oblique aerial photos are photos that are taken from the air but are not vertical. I assume these ones won't be much use for the image base.
Vertical 
Vertical (or near vertical) are what we need for the image base.