PHOTOGRAMMETRY VS LIDAR

The emergence of different airborne sensors for geospatial data capture has allowed working with different methodologies in cartographic production. For this reason, it is necessary to study the feasibility of the modern  technologies and their operative  development in order to achieve the optimized integration of  geospatial data.

   

 Every technological advance is an essential step to fulfill the needs of society, at the same time being important that the technicians responsible indicate the means of improving results in consideration of the different user capabilities. In this process the national cartographic institutions must give their professional advice and establish the working patterns normalizing the cartographic production criteria, so as to honour the purpose demanded by society. 

The current potential in cartographic production for information registration depends on the choice of passive sensors such as analogical cameras and matrix or linear array digital cameras; active sensors such as LIDAR and RADAR; information sources such as RGB, Panchromatic, near IR, intensity level, position (x, y) and height first echo ... last echo); sensor orientation through INS/GPS  and/or aerotriangulation; advantage out of the information (cartography, DTM, DSM, etc.) through photogrammetric techniques, LIDAR or RADAR.

In short, the production framework will depend on the available means and on the technical specifications set up for carrying out the work. We should take into account that the above-mentioned options – in addition to the traditional ones – allow the integration of information from the different sensors and its subsequent management in order to achieve the intended objective. This will be the subject of this paper along with decision taking and the pertinent quality control, as well as the exploitation of the information through the detection of changes and vectorization.

PHOTOGRAMMETRY VS LIDAR

	LIDAR	Photogrammetry
Energy source	Active	Passive
Geometry	Polar	Perspective
Sensor type	Punctual	Matrix or linear
Measurement of points	Direct without redundancy. Accuracy of information only depends on calibration of system components	Indirect with redundancy. Images with overlay provide the intersection of the homologous rays (HR)
Information type	Punctual. Reconstructed surface (type of material and observed structure) difficult to assess	May be punctual, lineal or superficial. Easy to interpret reconstructed model due to info source: the image
Sampling	Individual points	Full areas
Associated image	None or monochromatic image	High geometric and radiometric quality
Horizontal accuracy	2-5 x less than vertical accuracy	1-3 x better than vertical accuracy
Vertical accuracy	10-15 cm (~ 10 cm per 1,000 m on heights of 2,500 m)	Depends on flight altitude and focal length of the camera
Flight plan	More complete. Small passes. higher potential for data	Needs consideration of longitudinal and transverse coverage
Flight constraints	Less impact of time, daylight, night, season clouds	Daylight flying, clean atmosphere necessary
Production range	May be automated, thus a greater production	Higher need of editing control
Budget	25%-33% of budget: photogrammetric compilation
Production	Software: depends on qualified commercial & technical people	Software for the end-user: slow process of identification and manual extraction. Not reliable if automated, implies editing, especially at large scales.
Data acquisition limited by a largely contrasted area	Data can be acquired. Successfully used in coastal cartographic production	Difficult and expensive
Processing	Groups	Correlation
Feature extraction	Definition of zones or areas	Edge limits 2-D
Results	Edges or limits 3-D	Edges and zones 3-D