The idea of using a drone for mapping work is nothing very new but technology is moving so quickly that very soon you'll be able to use a DJI Inspire 1
(from £2381) or Phantom 3
(from £899) for professional quality missions. In fact a beta version of one of the most popular capture apps has been released for the two aircraft this week. Geospatial mapping involves taking a large number of overlapping, GPS tagged images while flying a pre-planned route over a location with a multi-rotor or fixed wing drone. Once you're sure you have enough accurate data it's a question of handing it all over to your computer and one of the many pieces of specialist software that are out there. The word geospatial is used to indicate that any form of data that has a geographic component to it. This means that the records in a dataset have locational information tied to them such as coordinates, addresses or postcodes. In the case of photos or scans from remotely piloted aircraft, they will be tagged with GPS information which will contain location and time markers. The applications are many and varied but include site surveys for the construction industry, environmental work, agriculture, archaeology, mining and quarrying. [caption id="attachment_1705" align="aligncenter" width="555"]
A photographic map of farmland[/caption] Of course the images don't have to be confined to normal photographs. Infra-red, near infra-red, and multi-spectral sensors can be employed. Lasers and LED sources can be used to collect LiDAR or LEDDAR data too. [caption id="attachment_1706" align="aligncenter" width="555"]
A laser scanned point cloud image of a forest[/caption] The advantages of using a drone over conventional aircraft and especially satellites is that the image quality will be much more detailed. A satellite image will probably be accurate to more than a metre while an image from a low altitude UAV can be accurate to less than a centimetre - a huge improvement. On some UAVs the GPS tagging may not be as accurate as is necessary, especially if the aircraft is moving quickly, as in the case of a fixed wing drone. Not all systems are capable of tagging down to the nearest millisecond so that could produce a significant margin for error. One way to make your map more accurate is to use Ground Control Points. GCPs are markers with accurately recorded GPS coordinates that will be visible from the air. This will help to align the captured images with the site that's being surveyed. [caption id="attachment_1718" align="aligncenter" width="555"]
Example of a ground control point[/caption] Where drones are needed to provide pin point accurate positioning for highly detailed missions, then after market options are available to replace or augment what is often consumer grade GPS system. Florida based Micro Aerial Projects, for example, have developed their V-Map system to provide centimetre scale accuracy. They say they have designed "a hardware configuration that integrates dual frequency GPS post-processed positioning capabilities with event marking, thus enabling precise positioning of cameras at the moment of exposure". [caption id="attachment_1709" align="aligncenter" width="555"]
Micro Aerial Projects' V-Map unit on top of a UAV[/caption] The cost savings over a conventional, fixed wing aircraft are considerable too, especially if companies hire in professional UAV pilots when they're needed rather than buying their own drones and employing full-time crew. In theory one or two people can deploy a drone on site and get the data down to a computer or up to the cloud in a matter of minutes. Some professionals in the surveying industry might be worried about the de-skilling of the whole operation but professionals would still be needed to ensure there are accurate ground control points on the site and they will certainly be needed to interpret the masses of the data that will be produced. In an article for the Land Alliance, authors Dr Janina Mera and Kevin Barthel had this to say: "Revolutionary technological advances frequently face the most resistance from the very people in the technical fields that stand the most to gain from the advance. Change generates uncertainty and fear. Fear the “machines” will supplant the practitioners. It is no surprise, therefore, to see hesitation and reluctance by surveyors and traditional aerial mapping specialists in light of the rapidly increasing use of Unmanned Aerial Vehicle (UAV) technology for geospatial data collection. "The fear is that with the UAV and the perceived largely automated process, the role of these traditional geospatial professionals will be diminished. This concern is unwarranted." Once the data is in your computer it's all down to the software. A quick Google search will reveal a plethora of options. The two packages that you'll probably see more often than others are Pix4D and Agisoft Photoscan. The appeal of Pix4D for DJI pilots is that the Pix4D app is already available for the Phantom 2 Vision and Phantom 2 Vision+ and, according to their website, a version of the app for the DJI Inspire 1
and Phantom 3
Advanced and Professional will be available very soon. A beta of the Android version was released this week. This is the app that allows you to plan and execute a photo-mapping mission. It's not a full autopilot so you'll still have to make sure your drone avoids obstacles and manoeuvres safely.
For the data crunching and the final visualisation of your aerial map you'll need Pix4D Mapper on your computer. You can take it for a test drive by downloading the Discovery version. After that you options to rent it monthly or annually or you can buy it outright. Rental charges are around £214 a month or £2140 per year so it's not cheap for the small operator. If you buy it outright the bill rises to £5280. You're covered for 2 computers - the theory being that you'll have one onsite for checking and another back at base for processing. In practice it's probably best to hand over the data gathered by the Pix4D app to the company that needs it because they'll have the financial and computer resources to deal with it. Pix4D's Krista Montgomery says "With the coming release of Pix4Dmapper Capture App 2.0, we're excited to offer Phantom 3 and Inspire 1 compatibility. We've gotten lots of requests for this and can't wait to see how our users react. The app enables users to get professional-grade mapping results with consumer-grade drones, and compatibility with DJI hardware opens doors to a larger audience." [caption id="attachment_1708" align="aligncenter" width="555"]
An orthomosaic map of a jungle area.[/caption] Agisoft's Photoscan is one of the other major players. Photoscan is available in standard (£114) and professional versions (£2240) and both can be tested as a demo version or a 30 day trial. The standard edition can perform photogrammetric triangulation, dense point cloud generation and editing, 3D model generation and texturing and spherical panorama stitching. Geospatial mapping is a huge area to cover in just one article so it's something we are bound to come back to in the future.