As my interest in mapping has grown I have put together this post to help me and remind me of certain things I hope it can also help you. Please leave a comment good or bad as this can help me to further develop the skills needed.
When I first left my higher education (college) I was employed by MDL-measurement devices ltd based in Aberdeen they specialised in laser measurement devices and the job involved putting the laser systems together I moved on from that roll to the oil & gas industry to further my career but now I have an interest in drone mapping I have circled round and come back to learn more. MDL have now been acquired by Renishaw.
So when you start your drone business or even before you may see a lot of software online and offline who help you provide 2D and 3D modelling using various methods, sensors (lasers/cameras/Survey grade equipment) and software the information you can provide is helping various Industries:
- Land Survey,
- Real Estate, Inspection,
What they may use the information for includes: site surveys/layouts which can be added to progress reports, inspections of the work site for hazards seen from a bird’s eye view, analytics of the work site by measuring stockpiles, CAD or 3D drawings I am sure the list goes on.
You can use software combined with your drone to provide the relevant information but make I needed to understand what the client wanted and if I felt comfortable to provide it, knowing what to do with these files before handing them over. E.g. a surveyor or architect will most likely require different file types. I have collected my notes to help anyone looking for a basic rundown of the mapping software I found and the acronyms which helped to further understand this subject.
Two Dimensional & Three Dimensional
2D will often refer to a two-dimensional space where there are two axis mathematically represented as the X&Y axis, with regards to geometry this would be the equivalent to a triangle, rectangle, square etc. Basically when a shape is drawn it would be flat on a piece of paper or could be displayed as a map without contour lines.
3D will often refer to a three-dimensional space where there are three axis mathematically represented as the X,Y & Z, with regards to geometry this would be the equivalent of a cube, sphere, pyramid etc.
As I mentioned above you have 2D and 3D, but it gets furthermore complicated when you throw in all the acronyms, phrases and file types. For example the earth its self is a sphere or to make things more complicated and ellipsoid, laying out a sphere or ellipsoid flat on paper as a 2D map will lead to some distortion the outcome is the same when displayed on a computer monitor and will need some sort of map projection correction. The standard for web mapping applications such as Google Maps is (EPSG: 3857) and Google earth uses (EPSG:4326).
Ellipsoid- An ellipsoid is when you take a Sphere (ball) and push down to distort what once was a perfect sphere, there are many different reference ellipsoids, the precise latitude and longitude of a point on the surface of earth is not unique unless the coordinate reference system is known this is especially important for accurate applications, like a Global Positioning System (GPS). ISO standard quote “without the full specification of the coordinate reference system, coordinates (that is latitude and longitude) are ambiguous at best and meaningless at worst”.
EPSG – European Petroleum Survey Group – “The International Association of Oil & Gas Producers” EPSG Geodetic Parameter Dataset is a collection of definitions of coordinate reference systems and coordinate transformations which may be global, regional, national or local in application.” The EPSG Geodetic Parameter Dataset is maintained by the Geodesy Subcommittee of IOGP’s Geomatics Committee. http://www.epsg.org & https://www.epsg-registry.org
Now we know that we have 2 & 3 dimensions, how do we know at what point we are located on the earth’s surface?
Latitude and Longitude are used together to pin point a location on earth’s surface. GPS
World Geodetic System– Is a standard used by GPS and it comprises of:
- Geographic coordinate system – defines three-dimensional coordinates based on the Earth’s surface e.g. Latitude, longitude and elevation.
- Spheroid reference – Datum (WGS84)
- Geoid – Involves the use of earths gravitational force and would be better to read on reference: https://en.wikipedia.org/wiki/Geoid
Global Positioning System – Originally created for use by the American military, the system comprises of roughly 30 satellites orbiting earth if your GPS receiver makes contact with a minimum of three through Trilateration your position will be known. Other countries systems include Russia’s (GLONASS), European Union Galileo positioning system (GNSS) , China’s BeiDou Navigation Satellite System (BDS) and India’s (NAVIC). Most drones are fitted with GPS, but extra systems have been developed to improve your accuracy when mapping.
Global Navigation Satellite System (GNSS) – receivers use the GPS, GLONASS, Galileo or BeiDou system and survey grade receivers can be used to position GCPs.
NOTE: As I am not a surveyor and in no way advertise I am I thought it best to have a better understanding to at least be able to understand what information they may require from my drone data.E.g. if you provide a map to the owner of the land, they may just want a layout so placement of houses etc can be decided. But imagine the information is passed to a developer/architect who starts to plan more detailed drawings based on your map (contours etc) he then hires a surveyor to quantify your results only to find the original map is inaccurate, this is passed to the land owner who is now upset as he thinks what you have provided is unprofessional and inaccurate waste of time and money. Questions you could be asked like was GCP’s used? What RTK sensor was fitted to the drone or was it PPK? Not great for business!
Adding Accuracy to your Map
RTK Real Time Kinematic –RTK positioning uses a base station placed at a known point (bench mark) and points are then taken with reference the base station. This may be used to quantify your GCP’s for relative accuracy; absolute accuracy is only as accurate as your base station. RTK receivers on board a drone can mitigate the need for GCPs.
Most drones are fitted with GPS, but extra systems have been developed to improve your accuracy when mapping.Check out the DJI system here D-RTK!
GCP Ground control points – Large marked targets which can easily be seen from your flight altitude are placed on the ground at strategically known points. These points are precise and the centre point is measured using extremely accurate equipment. These points should be spread out strategically throughout your map, often between 3 to10 points are used.
PPK Post Processed Kinetic – Similar to RTK but the positioning data is from the drone and base station are combined after the flight, the benefits being no loss of data link out in the field due to communication issue’s allowing the drone to fly further from the base station. Data can be processed multiple times to give more comprehensive results.
Relative Accuracy – Two points on you map can be measure via software and these will be accurate to the physical points measured.
Absolute Accuracy – A point is taken from your map and correlated against a point in the real world, the size and shape of objects will also be correct for absolute accuracy. Very important when overlaying your geo-referenced map onto a site plan.
Output files and storage Databases
GIS Geographic Information system – This is another hugely complicated subject and something you could study for a few years but from what I can understand what you need to know is that this is a computer system which holds/stores, retrieves, checks, manages and displays the data relating to the earth’s surface and various free software options exist. GIS systems tend to encode the raster pixels with pixel locations.
GeoTag – Before your image can be overlaid on the likes of google maps your camera should be able to perform Geotagging to the photographs metadata so your images are Georeferenced on a map the reason for this is so the software knows at what point in the world they relate too. This is normally done by adding the GPS- global positioning system points to the metadata it is not seen in the picture itself but instead in the .EXIF or. xmp file. Output picture files include .jpeg .TIFF .RAW.
Photogrammetry – involves taking measurements from photos and is as old as photography itself.
Orthomosaic or Ortho – This tends to mean a lot of pictures that have been stitched together and “orthorectified” and overlayed on a map to produce a very detailed picture which can be referenced for true distances as lens distortion, camera tilt and topographic relief have been removed.This is a map I created and overlayed onto an image taken from google earth, you can clearly see the difference in detail between the old satellite image and the newly created image. Output files include GeoTIFF, KML file, Google Maps HTML file
KML Keyhole markup language Files – based on XML standard. Tags are associated inside the file allowing the file to pinpoint locations or overlay images on Google Earth a great way to provide a more detailed image compared to the satellite image provided by Google.
Point Cloud – Can be collected using a laser scanner or converted from photographs (photogrammetry). The point is located in a space and is taken from on a physical object. Many points together will produce 3D representations (X, Y&Z) of the physical object. These can then be edited and computer generated or even 3D printed. Output files include.las, .laz, .xtz .ply (Auto desk.)
3D model – is a model from which a physical object is converted into a mathematical representation, this is done via special computer software. Output files include .OBJ .3DS .STL .FBX .DAE
3D Mesh – this is a textured representation of a model that can be overlaid to a point cloud, it includes the verticals, edges and faces.
3D video animation – Once the 3D model has been created you create walk or fly throughs of your 3D animations to better display and inform. Output files include .mp4 .mkv .avi
Laser Scanning or LIDAR – Is using laser beams in a controlled manor to take distance measurements from various angles and combing them to create a 3D model. So when do you choose LIDAR or Photogrammetry? Price and accuracy often have a huge part to play and also who is going to interpret the data. Engineers may lean more towards the LIDAR where as a site manager or customer might prefer the photogrammetry as the pictures are a lot easier to understand. As time progresses drones are looking to combine sensors and save on multiple flights and time.
Topographical – Topography is the study of the shape and features of the surface of the Earth, essentially “getting the lay of the land”, the topography of an area could refer to the surface shapes and features themselves, or a description especially their depiction in maps (contour lines). Detailed information about terrain and surface features like streams, rivers, forests etc is essential for the planning and construction of many projects.
Contour lines – Lines joined together to indicate terrain at the same level. Output files include shp .pdf .dxf
Raster & Vector Image files – Can be confusing but as I use these software packages I tend to relate best and remember Photoshop or GIMP edits raster images and InkScape edits vector images. But in mapping terms that’s not much use,
Vector = Points, Lines and Areas
Raster = Made up of pixels (grid cell) normally red, green or blue in colour. Each pixel has its own value e.g. a certain height or position.
BIM / Building information modelling/Model – is a digital file which represents an actual physical place and is created to help from the construction to delivery phase of various construction projects A BIM tends to include more than just a Length, Width & Height (3D) drawing it can include the time, cost, geographical data etc. The aim of a BIM file is to be handed over at each phase of a project from design, manufacture and operations/maintenance. Each phase would have specific data added and only one large file worked on to stop lost data throughout the stages. Output files include .IFC .DXF .RVT .DWG .NWD
The regulation/Specification for BIM is: PAS-1192-2-2013 (Incorporating corrigendum No1)
Digital Surface Model (DSM) – a model of the area mapped without colour information. Output files include grid DSM & raster DSM
Digital Terrain Model (DTM) – a digital terrain model is similar to the digital surface model but only as the name suggests terrain e.g. buildings filtered out. Output files include DTM, raster DTM.
Here is another map that was produced with 70 images stitched together using drone deploy, the flight was also controlled using their app.
Drone mapping software & applications
- Drone deploy – The reason I mention them first is they really hit the market about the time I started my own business and provide free webinars to sign up for which was great for learning more about mapping and why it could help so many industries.
- Pix4D – The leader and probably one of the mostly used software/app. (Quite expensive)
- Raptor Maps
- Precision Hawk’s Precision Mapper
- 3D Robotics
- Sense Fly
- Maps Made Easy- offer a pay as you map service which is very handy if you want to offer this as a service but do not have a regular need.
- Auto desk ReCap pro is a photo to Point-Cloud
Final Thought: Most of the apps allow the drone flight to be autonomous which can be very scary the first time you plan your flight and watch the drone fly off into the distance. Be very wary of your surroundings and complete a very detailed sight survey watch out for that telephone wire and always keep your drone in view. I am sure the software will also continue to improve and help keep commercial drone pilots in touch with the industries, who will require the need for the information. I have played around with two drone deploy more than any of the others it is a paid services but they do offer a free trial. They can benefit the smaller businesses as they offer the opportunity to have projects completed via the cloud saving investment in large amounts of computing power they would otherwise need. Read My review of DroneDeploy.