Survey

An orthomosaic image, also sometimes known as an orthoimage, orthophoto, or orthophotograph, is a high-resolution aerial image taken by a UAV. When stitched together with specialized software using a process called orthorectification, these images can be used to create a highly detailed, distortion-free map and enhance the visibility of details that may not be visible using more common photogrammetry techniques. Orthorectification removes perspective from each individual image to create consistency across the entire map while keeping the same level of detail from the original image. 

Orthorectified imagery differs from standard aerial photographs in the way that it visualizes perspective. Orthophotos are corrected for perspective, camera tilt, and lens distortion. Doing so means that these photographs can be scaled accurately from image to image, making for surveying measurements you can trust for true distances. That being said you’ll still need to use standard drone land surveying techniques like ground control points and calculating ground sample distance. 

Orthomosaic maps offer several advantages over regular aerial photos, however, a super high-quality image may not be necessary for every surveying job, especially considering the potentially higher cost. Orthomosaic maps are valuable for surveyors because they lack distortion and aren’t impacted by factors like perspective. They’re also easy to turn into interactive 3D assets. For worksites that require scalable maps with consistent details throughout, the orthomosaic option is simply unmatched.   

Orthomosaic mapping does have its drawbacks. The modeling style requires far more close-up images, requiring you to fly your drone closer to the ground. This may take more time than other methods. In addition, the kind of image detail that is the trademark of orthomosaic mapping sometimes isn’t necessary. For example, if you are only trying to determine the boundary of a piece of land or only need detailed imaging of a specific area, an orthomosaic map will probably offer very little.  

Surveying isn’t the only sector that can benefit from the use of orthoimages. Some of the most common sectors making use of ortho maps include:  

• Farming: Taking multiple orthoimages over time can allow farmers to spot patterns in how their crops are growing over time. This is especially important for monitoring crop health. 
• Law enforcement: Police officers and firefighters use UAV mapping to map out busy areas and crime scenes. With their higher level of detail, an ortho map may be able to capture important details that would otherwise be missed. 
• Real estate: Orthomosaic maps of properties can be turned into interactive virtual tours. This feature was especially important during the height of the COVID-19 pandemic when in-person property tours were limited. 
• Environmental conservation: Conservationists can utilize an orthomosaic photo to spot endangered animals in a set land parameter or capture change over time.

Across the board orthoimages and maps are useful for both detailed imaging and topographic accuracy. Whether you’re looking to use orthomosaic imaging for land surveying or one of its other wide-ranging applications, DJI has the ideal drones.

LiDAR is short for ‘light detection and ranging’. LiDAR sensors work by emitting pulses of light and measuring the time it takes for them to reflect back off the ground, along with the intensity with which they do so.  

Although it’s been around for decades, it’s only in recent years that LiDAR technology has become compact enough to integrate onto a payload that a drone can carry (L1 on M300).  

The LiDAR sensor represents just one part of a complicated process. To gather the data needed to build a point cloud that accurately reflects terrain and its topography, LiDAR incorporates other high-accuracy systems: satellite positioning (GNSS data) and an inertial measurement unit (IMU).      

With a little bit of software magic, LiDAR flights can be used to build 3D point clouds and intensity maps - both of which need plenty of skill to interpret but provide invaluable data in mining, forestry, agriculture, and construction operations.

The most cited positive of using LiDAR for mapping is the technology’s accuracy. But as a standalone statement that doesn’t give us much to work with.   

First, it’s important to consider what accuracy means for you and your project. Are you prioritizing accuracy that’s relative or absolute? In other words, are you concerned about your end product being accurate in terms of its features in relation to each other, or its features in relation to their place in the world?   

LiDAR is the way to go for absolute accuracy and is typically the best choice when the aim is a realistic bare earth model. That’s because it’s the best method for accounting for elevation, vegetation, and the conditions at hand.   

LiDAR’s integration with GNSS data and the fact that it’s a direct measurement - firing out thousands of laser pulses from above - ensure your final digital terrain map has extreme vertical accuracy.    LiDAR Topographic Map GIF Topographical complications don’t only come in the form of terrain undulations. Vegetation can also block photo-based surveying methods from getting granular ground-level data.   

LiDAR’s light pulses penetrate the gaps between leaves and branches, reaching the ground below and improving the accuracy of measurements.   

LiDAR is also preferable if the light conditions of your worksite are inconsistent. If you want to carry out night-time surveys or low visibility missions, LiDAR can handle the task without needing an external source of light.   

Lastly, LiDAR allows you to capture details that are small in diameter. A great example of this is power cables. Thanks to high-density point sampling and the direct measurement approach, you can use LiDAR to accurately map cable catenary.