Geographical factors and poor photographer skills.

Best Regards

Hi， Qayssar Ajaj

as a hobby GISer, associated my experience, photogrammetry can be applied to measure the length perimeter and area via the Remote Sensing without DIY, which makes geographic reasearch simper. However, the accuracy cannot be assured that in some particular condition, e.g. 3D space or even more dimensions.What's more, the climate factors, e.g. temperature, cloud, wind speed, solar radiation, must be taken into consideration.Hope it helps.

Broad question indeed. And imaging is not equal to photogrammetry.

I tend to agree with Dan Abudu on the focus of your questions i.e. remote vs on-site data collection and I would add that limitations can also come about in the equipment as well as the techniques used as a function of site geometry. You always assess method of approach on accessibility and site or project conditions then determine what equipment to use for a prescribed accuracy requirement. Another issue is the vehicle upon which the equipment is used i.e. are you working with a mobile or stationary platform? Terrestrial or airborne? How do you analyse the data upon collection? Do off-the-shelf software solutions exist for the task at hand if equipment used for data collection does not have an analysis package? Consider also time vs accuracy of final product depending on the size of area investigated. Climatic conditions may be an issue to adjust for as Chen Xiao Fish has mentioned. Lastly, all techniques and associated equipment for data collection and interpretation are borne out of human imagination and the desire to solve an existing problem, therefore the limitation is in our ability to imagine. Hope this helps.

I strongly agreed with the answer given by Chen Xiao Fish and Dan Abudu.

I will add to the other fine answers here to say that photography equipment and cameras are passive sensors, meaning that they do not generate light but collect reflected solar light. Where most field observations can be done any time of day under a variety of weather conditions, photogrammetry is better under sunny clear skies with the sun near its local zenith. If you want to collect repeat datasets for detecting change, collecting data under ideal sky conditions is even more important. Differences in daily solar energy and time of day can affect the amount and angle of reflected solar light and can introduce added uncertainty in surface charateristics or imagery band relationships.

The photogrammetry applications are limited when there are no sufficient illumination. In addition, where there are canopy covers, the accuracy of the measurement is limited due to light ray obstructions, and since it can not project its own light source.

It also depends of the context of application (aerial/ground acquisition, medical application). For example, in medic application the main issue is the invasive aspect of the method.

Limitations in Photogrammetry are:

(1) Visibility, the photograph records whatever is visible, and visible by the camera lens in the visible spectrum and near-infrared.

(2) There must be a proper overlap to ensure that whatever is to be mapped must be recorded in at least two photographs each taken from a different camera station with a good base to height ratio. The base is the distance between two successive exposure stations and height is the distance between the camera and the object photographed.

(3) The accuracy depends on the image scale and image scale depends on the camera lens focalength and on the distance from the subject. Therefore image scale must be appropriate to ensure the satisfaction of mapping accuracy specifications.

(4) The object to be mapped must have a minimum texture to facilitate the image correlation of overlapped images and identify the same ground point in two overlapped images.

(5) Flight planning must be properly performed to secure overlapped coverage, especially in rugged terrain.

The presence of a special aircraft and a photo camera, the choice of photogrammetric technology, the timing of aerial photography under appropriate weather conditions. the presence of phobogrammetric instruments and software, personnel, the cost of the final product for a given accuracy.

Hi

Photogrammetric constraints are discussed separately in the flat and three-dimensional models.

In preparing the map flatly, the main limitation of photogrammetry is the pixel dimensions of the image on the ground because it will determine the scale and quality of the map produced.

In preparing the map in 3D, the main limitation of photogrammetry, in addition to pixel dimensions, will be the ratio of the aerial shooting distance to the platform height. The closer this number is to 1, the better the ideal state for extracting altitude accuracy.

Hi Qayssar. Photogrammetry requires light to provide reliable information about physical objects in the environment. This poses challenges, for example, when clouds are formed, and during rainfall and snowfall. This renders some applications of this technology context-specific and weather dependant. Recently, it has also been regarded as being susceptible to hacking practices, as everything digital.

In my experience the biggest limitation is the user itself. You need to have good skills in photography (manual mode) and be very familiar with photogrammetry principles. You need experience of course also. I am talking more about terrestrial photogrammetry.

@Qayssar Ajaj

It is undeniable that photogrammetry is a very effective non-contact observation method. However, it also has some limitations:

It is undeniable that photogrammetry is a very effective non-contact observation method. However, it also has some limitations:are equipment, such as the image pixel quality of camera;

2. The matching algorithm of stereo image pairs, such as image batch matching algorithm and scale conversion, is difficult;

3. Photogrammetry does not have penetration ability for observation with occlusion, for example, canopy occlusion makes it difficult for photogrammetry to obtain tree factors above and below the canopy at the same time;

4. For terrestrial photogrammetry, the operator's photography skills are required.

5. In addition, photogrammetry also has certain mandatory requirements on the observation environment, such as illumination, rainfall, cloud and fog.