How can 3D maps be made with ordinary photographs? by Adam Steer

An ordinary photograph is really a two-dimensional model of a three-dimensional world. We can also reverse the process - and figure out where an object in an ordinary photograph was positioned in the real world.

To do this we need to know a few things about the camera - we need to know how it made the two-dimensional model.

If we know about the camera and have two or more photographs that overlap, we use the camera information, image properties and matching objects in each photograph to figure out where each camera, matching object and potentially every pixel is in three-dimensional space.

So it is a big circle! A camera makes a two dimensional model out of three dimensional things. These two-dimensional models can then be combined to reconstruct a three dimensional model – which can be used for surveying tasks which are not so easy with the ‘real’ things.

Adam Steer

Every wonder how Google Maps knows where/when there is traffic? by Walter McGee

Data is collected from various sources, dependent upon: 1) how urbanized the area is and 2) the nature of the street (ie, hwy, surface road, etc.).

Real-time Traffic Sources:

-Pole mounted radar

-Surface/Ground sensors

-Video cameras

-Cell phone GPS

These are usually found in urban or on high traffic throughways and often feed a city's traffic management system. This is provided or sold to a reseller (like NavTeq) and then to Google Maps.

Cell companies can pull velocity from your phone's GPS and/or cellular tower triangulation. Nearly all streets in the US are digitized and have defined speed limits. Cell phone data is generalized, the avg. velocity is calculated, and correlated to the speed limit on that road segment. Once a threshold is met (say 60% of the speed limit) for a certain amount of time, a line changes colour and is fed to any number of online mapping systems.

Walter McGee, Operations Planning Coordinator, GeoDigital International Inc.

LiDAR by Jim Roby

LIDAR is similar to a radar but sends out a packet of light at a specific wave length. In the case of a wind finding LIDAR, the wavelength is 1.5 to 2.0 microns which is a very short. A certain portion of the light is reflected back to a special "telescope" which is sensitive to the wavelength of the emitted light. i.e 1.5 to 2.0 micons. If the emitted light encounters any object, (in wind finding the objects are small particles of naturally occurring aerosols,) the time and magnitude of the reflected light is received via the telescope by very special detectors. After the return signal is processed, the results can be the velocity of the aerosols which is also the velocity of the wind moving either away from or toward the telescope. Using time, we then know the distance of the computed wind vector. Thus we have a Doppler LIDAR that in concept is exactly like the RADAR. If the light is emitted via a two axis scanner, we can measure the wind velocity and direction surrounding the LIDAR.

By Jim Roby

LiDAR by Jethendra P N

LIDAR (which stands for light detection and ranging), like radar, is and active remote sensing technique. The use of lidar for accurate determination of terrain elevations began in the late of 1970s. Initial systems were profiling devices that obtained elevation data only directly under the path of the aircraft. This technology involves the use of pulses of laser light directed towards the ground and measuring the time of pulse return. The return time for each pulse back to the sensor is processed to calculate the variable distance between the sensor and the various surfaces present on (or above) the ground. Advantages of these LIDAR systems afford the opportunity to collect terrain data about steep slopes and shadowed areas and inaccessible areas ]Modern LIDAR acquisition begins with a “photogram metric aircraft “ equipped with air bone GPS (for x,y,z sensor location),an Inertial Measuring unit (for measuring the angular orientation of the sensor with respect to the ground ), a rapidly pulsing (15,000- pulses/sec)laser , a highly accurate clock , substantial onboard computer support, reliable electronics, and robust data storage . modern system are able to record up to five return per pulse. Which demonstration the ability of the lidar to discriminate not only such feature as a forest canopy and bare ground but also surface in between (such as the intermediate forest structure and under story ). Flight planning is crucial, so that data are collected for the entire project without missing areas, causing gaps between flight lines. The distance between sampling points is derived from the altitude and speed of the aircraft, the scanning angle, and rate. As with any airborne GPS actively, the LIDAR system require a surveyed ground base location to be established in the project are as differential post processing correction. In addition, a calibrated alignment process for the GPS position of the sensor and the orientation parameter is required to assure and verify the accuracy of the lidar data sets. These lidar applications are particularly well suited for generation of digital DEMs, topographic contouring, and automatic feature extraction. The whole lidar technology uses laser beam to scan the earth surface. Laser scanner mounted in aircraft emits laser beams with high frequency and receives the reflected beam. Time difference between emission of laser beam and reception of the reflected laser signal is recorded to get the distance (range). High frequency rotating mirror placed in front of the laser converts this laser into a laser scanner. GPS data recorded in air and on ground (DGPS base stations for every 25 kms) determine aircraft position. IMU record attitude variations (pitch, roll and yaw) of the platform for carrying out attitude corrections for the laser beam.

By Jethendra P N

What term GIS means? by Chris Rohe

Have you ever heard the term GIS? 
GIS stands for Geographical Information Systems, and what does that mean? 
It’s basically smart maps. Digital maps that have associated data that is open to analysis. When you open a road map on paper, the map reveals a great deal of information but this information is stagnant in that it can’t be queried. 
With GIS we can ask the map questions by querying the databases associated with the map. Every feature or object we see in the GIS map has attributes that are stored in a computer database. The database is information about the features you see on the map. This provides a powerful tool compared to an ordinary map. It allows the GIS user to analyze and create new information about the map they are looking at. 
Hence the term GIS (Geographical Information Systems).

Chris Rohe, Owner/Contractor, Grid Line Mapping, Sierra Vista, AZ

Aerial LiDAR Sensor by Scott Lehr

Imagine your standard Laser pointer flicking on and off; now imagine that pointing down from a helicopter flickering at a 100 000 times a second.  With an accurate stopwatch measuring the time from pressing the ON button to the time the dot hits the ground, and knowing the speed of light, you can calculate the distance from the ground.  Now imagine that laser hitting a spinning mirror like a grocery-store bar code scanner and you could keep track of the mirror angle of each flicker.  You are now spraying the ground with LiDAR.

Knowing the angle and time information you can create a point in space with a three dimensional coordinate. To create a point cloud (Millions of Points in Space) you add finely tuned GPS data and compensate for aircraft pitch, roll, and yaw.

Scott Lehr, BA, ADiGISA, GeoDigital Acquisition Group

LiDAR by Mukesh Vyas, GISP

Human eye is similar to the sensor which fires pulses and senses color, intensity, texture, etc., in 3D. 
Human brain is the processor which calculates and stores information like location, position, etc., of each point captured by the eye. 
Eye captures millions of points and collectively those points become a cloud (of points). 
In other words, eye detects light and brain calculates range of the object from where light is reflected...that is why LiDAR is known as Light Ditection And Ranging.

Mukesh Vyas, GISP

LiDAR is like an invisible rain! by Gurudatta K.N.

LiDAR is an advanced form of field survey, resulting in a cloud of points simulating the field.

To understand LiDAR, just look through the window on a rainy day. Observe how the rain drops from the cloud and hits the ground. On its way, a particular rain drop can hit a tree and then can further hit a roof and finally reach the ground. There will be millions of such rain drops.

In a LiDAR, the cloud is the emitter, the rain drops are the Laser beams invisible to naked eye, only difference is the laser beam after hitting its target, returns to its source. The various target hits are called echoes and are millions in count. These echoes convey their geographic location and elevation above ground. This type of LiDAR is known as Airborne LiDAR.

A garden water sprinkler represents Terrestrial LiDAR and when it’s on moving vehicle, it becomes Mobile Terrestrial LiDAR.

Gurudatta K.N., Project Manager - LiDAR, Egis Geoplan Pvt. LTD

Geophysical Exploration by Chris M. Rohe

Geophysical exploration is the use of instrumentation to create an image of the underlying ground.  

Have you ever wondered how they know where to drill for oil or create new mines?  

Geophysical exploration is a means that is used to accomplish these tasks.  
The term geophysical refers to the physics of the earth.  There are natural forces that flow through the earth, such as magnetics and electrical currents.  These forces can be used to determine the makeup of the ground beneath us.  
Computers and equipment have been developed over many years that can record these forces and give us an understanding of the substructure under our feet.  

So, when you hear the term geophysical exploration remember, it is a means by which scientists can use technology to determine the geology that is beneath the earth’s surface.


Chris Rohe, Owner/Contractor, Grid Line Mapping, Sierra Vista, AZ

LiDAR is basically just a digital 3D camera by Ted Knaak

Everyone has a digital camera. 
It's pretty common knowledge a digital image is a flat array of pixels. 
Each pixel has a combination of red, green and blue to recreate the captured color at that point. 
Now imagine that in addition to color, you could capture the location of each pixel in space. 
Now the pixels aren't flat anymore. 
Collectively they are a "cloud" of points which represent the scene in three dimensions. 
LiDAR produces this "point cloud" and is basically just a digital 3D camera. 

Ted Knaak President at Certainty 3D, Orlando, Florida

What is Bathymetric LiDAR? by Peter Hobson

Bathymetric LiDAR is an adaption of terrestrial (land) LiDAR which uses the focussed, coherent, light pulse to penetrate below water in shallow, clear, rivers, lakes, and seas. Bathymetric LiDAR Systems use pulses of 2 wavelengths of light, one (Green) penetrates the water column, and the other (Red - standard terrestrial LiDAR wavelength) is reflected from the water surface. 
The difference in range between the 2 co-axial pulses gives the raw (uncorrected for Tide and Waves) depth. 
Combination of returns generates a digital terrain model of the sea bed, and further information about the nature of the seabed and the water column can be derived from analysis of the returned pulses. 
Bathymetric LiDAR Systems have economic advantages over conventional survey methods along coastlines, and in areas which are difficult and expensive for vessel based survey systems to operate. 
They are limited by the turbidity (clarity) of water columns, and thus not efficient everywhere.

Peter Hobson is founder and Director of Waywiser Hydrographic Consultants Limited, based in Plymouth, UK. Over the last 12 years he set up 2 Bathy LiDAR companies - Admiralty Coastal Surveys AB and PELYDRYN Limited.

What is LiDAR? (example)

LiDAR is similar to radar in that it is an active remote sensing system that sends out a signal and records the time for that signal to return.
In the case of LiDAR the signal is a laser beam which can be used to determine the location and shape of objects in three dimensions.
The LiDAR sensor can be mounted on many platforms including stationary tripods, moving vehicles and helicopters.
The active design, versus the passive nature of a camera allows LiDAR to overcome many of the limitations of aerial photography.
This combined with the relatively high vertical accuracy of the technology makes LiDAR the sensor of choice for vegetation and corridor management.