What is orthophotography and Lidar?

Good Question! What is orthophotography and Lidar?.  In today's post we shall delve into the meanings of these terms a little more and hopefully gain a better understanding.  First of all lets start with aerial surveying, since that is what a lot of people percieve this profession to be.  Aerial surveying in the broad sense of terms can use multiple methods to accurately get the picture.  There is as we know aerial surveying to be, which would be the classic photo gained from flying the mission using the flight plan, photo control points, and a fixed film or digital camera such as a leica ads80.  The resulting photos can have different traits attributed to them as well.  These traits differ based on the customer's needs and usually range from whether they are in color or in black and white even to the resolution needed.

So what is orthophotography then?  Well exactly defined orthophotography is a "Photograph having the properties of an orthographic projection. It is derived from a conventional perspective photograph by simple or differential rectification so that image displacements caused by camera tilt and terrain relief are removed."  for a list of definitions on this matter visit http://www.maps-gps-info.com/maps-gps-glossary-o.html.  To get a better idea of one looks like I have posted a picture to the right for your viewing pleasure.

Lets talk about Lidar shortly.  Lidar is how we get topographic maps.  Imagine if you wanted to know what the Grand Canyon looked like; to find this out you would look at contours on a map.  Imagine that you had to draw everyone of these contours.  Instead of having to draw multiple contours, there are sensors that can do this for us.  By attaching a sensor to an aircraft, and flying the mission, it is possible to figure out these contours by basically scanning the canyon without actually having to go into it, just by using a laser.  Simply explained that is lidar.  I highly recommend the article The uses of LiDAR technology.

Basically in brief that is orthophotography and LiDAR.  These are both a form or aerial survey.  Without the aircraft and the sensors, finding out what our physical earth actually looked like would take longer.  In all the technology is there and it works.  Without this technology, we would be surveying contours every 50 feet and would not even have a way to see it from the top.  Although there is nothing wrong with this, it give those such as engineers, land managers, and GIS databases among others a valuable tool.

What Is It Used For

Aerial surveys and remote sensing techniques can be applied to many different applications.  Often aerial surveys offer county assessors, city planners, developer, engineers and others a way to look at a high quality, high resolution photo to be able to make informed decisions.  This can also be used by industries such as forestry to track changes in tree growth, or animal migrations.  There are even ways through remote sensing that a soil analysis can be conducted, ways to map archeological sites or find illicit drugs such as the example in the link for the article Hidden Villa marijuana raid nets 32,000 plants.  My favorite use is definetely aerial survey, just for the fact that surveying is one of the oldest professions known to man, and just by the fact that we live in a beautiful world.  For a more in depth look at this topic, click the link below.

http://www.schoolsintheusa.com/careerprofiles_details.cfm?carid=334

How are Aerial Surveys Gathered?

There are many ways to gather aerial surveys and historically in the past, even pigeons have been used.  Typically aerial surveys are gathered through the use of an aircraft such as the one shown (operated by Keystone Aerial Surveys Inc.) in the picture in this post.  You will notice it is necessary to cut a hole in the aircraft to mount the camera.  This type of platform will give you high resolution photos, which can be used in many various applications.  These applications include everything from engineering to forestry and even more.

For a more detailed explanation check out the article called "Remote Sensing Survey Strategy" at  http://www.searchmesh.net/default.aspx?page=1726.