Photogrammetry is specifically a method to carry out surveys and prepare maps using photographs. It is an art, science, and technology of gathering reliable data concerning any entity. This method involves a method of record-keeping, measuring, and evaluating terrestrial and aerial images. Photogrammetry, in other words, is the methodology to make measurements with the help of photographs.
Photogrammetry is a combination of three different words; Photo – light, Gram – drawing, and Metry – measurement. So, photogrammetry means merely light, pictures and measurements. The technology proves to be useful in creating maps. The user designs maps with the help of photographs clicked with the use of drone cameras.
1. Terrestrial Photogrammetry
Terrestrial photogrammetry is the one that consists of performing measurements by taking photographs from some specified positions on the earth’s surface. This category of photogrammetry uses photos taken with regular camera and theodolite.
2. Aerial Photogrammetry
Photogrammetry uses drone cameras or cameras mounted on aircraft. Aerial photogrammetry not only has higher precision but also has higher accuracy than the terrestrial photogrammetry.
Lidar (Light Detection and Ranging) is the method of remote sensing which uses light pulses in the form of a laser, and the receiver senses the reflected pulses. To take the measurement of the time required by the pulse to return to the receiver, the distance calculation takes place. Once the light pulses are merged with other essential data gathered with the use of aircraft, the user correspondingly gets the properties regarding its surface, together with some three-dimensional data regarding the earth’s shape.
A LiDAR mod mounted on the planes comprise mainly of a laser emitting device, a scanner, and one GPS receiver. The aircraft (airplane or helicopter) installed with the mod transmits the pulses to the ground.
1. Topographic LiDAR
This type of LiDAR implements aircraft with a device that continuously transmits infrared signals for mapping the land. In this, an airplane or a helicopter floats in the air over the ground to be mapped, and furthermore, it continuously emits the infrared pulses to the field.
2. Bathymetric LiDAR
Bathymetric LiDAR is the one which uses green light that penetrates into the water bodies and determines the elevations of seabed and riverbeds. This LiDAR system is suitable for creating shoreline maps and prepare the elevation models in digital forms.
LiDAR has rather proven to be delivering useful grades of accurate data. On the other hand, the technology is quite flexible for the scientists.
When it comes to comparison between two different techniques for the same thing, in particular, accuracy is the primary thing that a user might consider before using any one of them. LiDAR, of course, gives you the best accuracy than photogrammetry. However, both the technologies are widely used as per the users’ feasibility. Specifically, they are ideal for carrying out different tasks.
To sum up, photogrammetry is easier than LiDAR, but LiDAR is ultimately the best one out of the two.
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