Lecture 06

[Music] welcome back uh so in this lecture uh uh we are uh going to quickly look at uh what is stereoscopy and why it is important and uh we will also look at uh uh the type of cameras uh which are used uh in uh collecting the stereo photographs and as well as the about one or two cameras which are been used uh um and how actually the data has been collected through the satellite uh so stereoscopy as uh I have mentioned a bit uh in the previous lecture that uh this helps us in getting the uh 3D prospective view of the terrain so let us look at that word exactly is the stereo the stereo word originates from Greek and means relative to space actually okay so earlier uh usually we were using this word and this is commonly used as for the uh stereo sound and all that so we uh when we talk about the stereo we usually refer to stereophonic sound uh so originally the term was associated with stereoscopic pictures okay uh which were either drawn or photographed so in order to avoid the confusion with the stereophonic sound we often talks about the 3D picture so instead of calling the uh the 3D picture um as like and having the confusion between the stereophonic and stereoscopic pictures it is usually we started using 3D um uh uh pictures okay and and uh in like last one decade or maybe more than that uh there were uh television screens which used to come when uh we say that okay we can view the picture in 3D films actually mainly so uh we used to have the the goggles of the different uh uh color um IPS and then that can be used to have the 3D uh films to be viewed and so B basically this is the the word which is using we are using the stereoscopy is uh it stands for three dimension so uh uh further if we look at uh the more details about that uh so basically what we are doing is that we are uh viewing the uh the image okay on the photograph which are taken uh uh before and by forward and after uh uh cameras uh by either by the satellite or even if you try to uh look at like using uh uh the uavs that also uh shows so this is for example this is your right eye and this is Left Eye so what you are viewing is that this object here which are taken by uh uh um either by the same camera but at different angle covering the similar area and as we have discussed in the in the in the last lecture that uh uh while uh if you're having the uh the flight okay then you have uh like uh 60% of overlap over here okay so this should be your 60% of overlap so that will give you and uh uh uh advantage to view the terrain in three dimension okay so what we are be doing that we are not uh viewing the uh so if uh with the right eye you view the Right image and with the left ey you you the left image okay then and then what you will see is that you will be getting the pseudo stereo uh scopic model in and in your brain and that will give you an idea so the a pair of stereoscopic photographs or images can be viewed stereoscopically by looking at the left image with the left eye and the Right image with the right eye and uh this is this you can do using the stereoscope also or you you can use the uh What uh uh we can say the different uh color uh glasses so that will help you in viewing the this okay so this is what we call the stereoscopy so the I base at so this is your I base actually okay so this will be your I base so I base and the the photo base must be parallel in order to view the stereoscopic model so that should be there so that that that one can do even so as I told that you can use the stereoscope that I'm I'm going to come to the next slide in that or you can also use your normaliz to view this okay but that need practice okay so basically what we are doing is that the L lens of the human eyes project two slightly different picture onto the retinas which are then transformed by the brain in a seal representation and this um actually uh is what we are talking about the getting in stereoscopic image okay so the actual stereographic seal observation is a result of this perception through both the eyes so you need to have if you you just close down your one eye and then try to see the Right image and then the same you can do for the left and then open both you'll be able to see the 3D using uh stereoscope okay so for example this is an um if you have an practice and uh if you have uh like uh uh good practice in viewing this you can view this image again in three dimension okay but at at least you need uh like two photographs of the same object taken at different angle so for example this is the terrain again this is your uh uh low angle uh low oblique aial photograph and uh this is again the same okay but uh of capturing the same area Okay so if you you have an overlap here and this is mostly almost major overlap we can see because you have uh this portion which has been seen here and this hill is seen over here okay so this I'm having more than uh 70 to 80% uh overlab but this was been taken uh using with the digital camera and through the aircraft but that this can again help because both the photographs have been taken by the same camera but at at a different angle that is your view angle what we are talking about so that can give you again the three-dimension view of the terrain now advantages of stereoscopy if you take um has an ability to extract three dimension information example classification between the elevation difference tall trees or low trees you are having terrestrial features such as height of the teres these are all fluvial U landforms which we are going to talk in uh uh next lectures okay uh coming lectures with what what are the different landforms and all that okay so you will be able and even you can have uh talk about the slope gradient you can extract the slope gradient if you're having but Bas but with the with the help of uh the stereo photos you will have to plus plus the DM or you can say DSM that is digital elevation model and digital surface model and this will help you in generating or extracting I would say extraction of uh topographic information as well as you can do uh like uh a mapping of landforms with different elevation see this you can you can do very easily if you are having the mainly the stereo or you can say the 3D image and as I told that this is all going to be now in digital platform so you can extract this even DM in digital form okay then as I told that uh along with the the landforms here this again related to the rever landforms you can prepare a detail geomorphic map so extraction of topographic information mapping of landforms this will be like what you're are going to talk about uh the mapping of the morphology of the uh surface and that what we call geomorphology you can also if you have the almost like vertical photographs you can um map uh uh the strike and dip of the uh the stet is also exposed in in in on Surface now type of uh uh stereoscopes if you take uh this is there it is this this one is pocket stereoscope usually what we call and the pocket stereoscope will have uh uh just two lenses okay that uh so uh you can adjust this this this can these are adjustable and this is and you can fix this uh adjustment can be like you can move out and in there is depending on the uh your uh I base so depending on the ibase you can do that and then you can put the photographs here so one photograph has been kept here another has been kept here and we can view the the 3D and this okay so this is one that is what we call uh uh spocket seros scope so what we have here is this is this is the Plano convex lenses okay so these are all uh the lenses what we are having at the Plano um Plano convex lenses uh mounted so it is very uh like commonly used uh uh pocket stereoscope so usually if you are having uh these stereo photographs you can carry it in the field and then try to view the terrain in three dimension and then uh we have another one is is the mirror stereoscope okay so what it has here is that you have the uh two fixed mirrors so on this side these are having the mirrors actually here so you have uh the two mirrors here one is is this one and this another one so so it consist of two mirror fix at an angle of 45° okay so this is the angle what we are having is 45° Okay so this is another mirror here and that and those are supported by the four LS and at the high piece two prism okay so over here in this um two prism or small mirrors are fixed at an angle again at 42° 45° okay so the advantage is that one can view the terrain the phot in The Wider perspective so mainly you can have more area you can view more area when you're using the miror stereoscope you can also change like the ipce uh resolution and you can have like uh 2x or 3x something like that okay so you can have so that will help you in magnification okay that can help you in magnifying or magnifying the the the area of Interest checking that you can do even this what you have you can see here uh the the calibrating Rod has been shown here so this is also uh been used to uh do uh appropriate measurements in terms of the distance in terms of calculating the height of the object and all that can be done okay so this is an advantage of having the mirror stereoscope okay and Al also the last point which has been shown here the this one that you can what you can do is you can put uh uh the tracing sheet on one of the photograph and then trace your features okay very easily so you can side by side manually you can prepare your Maps depending on what information you want to extract out of this so this is uh uh the difference between the pocket and the mirror stereoscope now procedure for aial Photograph interpretation is the the most important is that you need to have the overlapping aial photograph and unless and until you are not having this you will not be able to uh view the 3D and then to identify or locate the principal Point okay on each photograph okay and draw the straight line passing through each of the principal points okay so if you have for example you have one photograph here okay and this we have uh discussed in the in the previous one also I'll just uh uh try to explain quickly so if suppose you are having uh uh one photograph and Then followed by another one and of course you have like what we were talking about that you are having like 60% of overlap over here okay this is one one very important point and this goes over here okay but the other part was that we were talking about in the previous lecture about the ficial mark ficial AIS and all that so if you if you draw the uh the ficial axis y and x y and x here okay you get a point here this is your principal point so this is say this is your photograph P or uh any any number you can give okay so for example like A1 I'm giving here and this is A2 here okay so this will be your principal point one and this will be your principal point two okay so when you when you connect this actually then that will give you the line of light okay and also the place uh place the photograph on the desk this is this I we will we have talked about this but the other point is is leftt out is place the photograph on the desk one overlapping the other with about 2 inch between the corresponding image using a straight edge or the scale edges a center line to Common line this is because if you adjust this properly this two points and all that so that will help you you in getting the 3D suppose your line of light is coming something like this okay then in that direction you will have to adjust your photographs okay but the in this case since it is all both the points are in the center so this will be your line of light here okay so for 3D also otherwise if if it is slightly like tilted then maybe you we will have to put your photograph something like this okay both the photographs and then you have to view the photographs okay so this can be done easily when you are using the stereoscope but as I told that nowadays we have an advantage of putting everything on digital platform and can be used okay so if stereoscope vision is not obtained slowly slide uh one of the photograph and try to it oriented at least um align the established line that is your um uh line of FL okay so that alignment is very much important okay otherwise you will not be able to see uh the 3D image and one can also try to align uh the uh the object okay so you can you can uh fix up one of the like uh try to focus on uh one of the object and try to match that object in other photographs also that can be easily done okay now coming to the principal point which I have explained over there okay so you have X and Y AIS and if you connect the ficial marks that uh will give you the intersection will give you the point and that point is your ficial mark So or sorry ISR uh principal Point okay so for this you have the the principal point is this one for this image and this image the principal point is this one okay now uh sometime it has also been filled that you need to have the the conjugate points to have an better alignment and understanding or you can uh say that identifying the line of light okay so for example for pro uh uh image one this is your uh principle point for image two this is your principal Point okay and then when you yeah like you you can you can do one thing you can trace out this point here and then uh with the uh maybe at the same time what you can do is you can just mark one of the the object here or the landform and with the same you can uh with the you can move your uh sheet or tracing sheet on the other uh image and then you will you will see that the the principal point of the second photograph will not match the principal point of the first photograph okay because there is an difference while taking the uh the photograph okay they are taken by at a different uh time at different angle okay but viewing the similar area or the I would say the same area so that when you when you do that so this point May lie somewhere over here and that will be your conjugate Point okay so that this is the conjugate Point similarly you can do it for the other photograph also so this is the conjugate point of the photograph 2 which has been transferred to your your transferred to your first photograph and similarly the conjugate principal point of is transferred to the next photograph will be your conjugate uh point so this is your uh conjugate Point uh of the first photograph which has been transferred here and this is the conjugate point of second photograph which is transferred here and this is pp2 this principal Point here and this one is pp1 okay so that how you can do and this helps in identifying so when you connect this this will help you in identifying the line of light okay and that what I was talking about so if you if you have put the photograph straight and you are trying to view like this you will not be able to view the 3D okay so unless and until you have not oriented your photograph to this okay so line of light will help you at least in understanding that what is the the sequence in which you are your uh photographs will been taken by the flying object okay this is one exercise which you can do uh and holding your like two fingers and uh bringing close to them uh to towards each other and at one point of time without touching the finger okay you will find that there is an image which has been formed in the center and that is floating and that is your what you are looking at the three-dimensional image okay so this you can you can practice okay so what you can this is what has been shown here so you you start bringing your fingers like you start bringing your fingers towards each other and the time will come that you will find that this is this portion of the finger is floating in the center and you haven't touched both the fingers okay so this is what the exercise helps you in uh uh practicing for the for the 3D image or you can view the studo pair and try to see the 3D perspective of the image okay now coming to other part is that camera films what we are having so usually uh uh those who are uh aware about the cameras so we have lens shutter and aperture okay so lens can be characterized by focal length and that what uh we can easily find out with the what type of lens and what uh and shutter speed and aperture and all that but the other point which I'm trying to explain you that there are C cameras and that is what we call frame cameras which will collect the data like in like portion wise okay it will not be continuous data here so it will keep on clicking uh the different images uh in in particular frame okay then you have another what we call the continuous uh strip uh cameras okay so this was frame cameras so you have one frame here second here three here like that okay but this one is continuous okay so continuous strip will keep on uh recording your data okay and then you are having panoromic okay so panoromic will definitely what you we we we were discussing but we have we'll have Distortion in uh uh so so the the data which will be collected will be um something like over here so you will have you will keep having the the strips uh going on on in this direction okay but uh so I'll try to put it a little better in a better way so you're having the film here and this is the area which has been and then second one will come somewhere over here like this but this so so this will be basically uh collected in in and strips again but in taking the panoramic view of the region okay and and another one is mostly used for that what we were talking about the stereo photos so this is what you have the forward uh camera and you are having the after camera so forward camera is taking the photograph of this area okay so you have the the gra of this area where is the so has been taken by this one forward and after you are taking this one okay so this is uh basically the the camera used to collect the corona photographs which I was talking okay so as you move further keep uh moving further then you keep on taking the uh the photographs of the the same area which has been taken by forward and then here what is been taken so already this area was been taken by the forward image and then it was taken by the after image okay so if you the the fly keep uh the satellite keep on flying like this and you keep collecting the data over here okay so this is the the part of the the corona photograph now Corona photograph resolution is it like the data comes in some something like this okay so you are having this strips here uh collected by the forward and after camera and they come uh in negative and you can you can have the uh the you can enlarge it and print it okay so what we do is that after knowing the line of light and all that so at least what we do so in in previous one it has been if I'm not wrong it is right now yeah it has been shown here so this is this is your another Point here okay so you have along away from the another will be some Distortion okay so so for example this is the another here and this one is another so this will perfectly will be almost vertical here okay so what we do is that to have uh at least uh the the uh 3D image so we try to uh like uh develop the the photograph covering the same area and uh we obtain the paper print okay and that can be viewed in your like uh uh like hard copies you can use that okay so you will have again that that you can do okay with so the area uh the size of the the negatives are 5.5 cm to 75 cm so so this is uh 5.5 and this one covers here almost like uh 75 cm you have okay and the area covered along the width okay that is along the width is along 7 19 km by and total if you say then that is around 230 km um of the area has been covered here okay then this is this is what we are having the corona image which is developed okay from the negative so you can have very high resolution um image of the and this is what we have uh Mosaic uh number of images and uh and to view the terrain and overall see this is this is what we are looking is a 2d actually 2D image but if you have the similar uh like after and forward photographs of the same area you can view this in three dimension also so this is what uh uh one can use okay this is we can so the distance here uh if I'm not wrong is this has been enlarged photograph but uh the distance between um if you have to quickly view this so distance between this two like points for example if I take okay same points then that that should be around 6 in or so so that can be done so when those who are having in good practice of viewing the 3D image or or viewing the stereo images uh with naked ey then uh this distance is fine okay so then one can view this in three dimension okay easily or even you can use the stereoscope pocket stos scope and try to view this in three dimensional for Publications also we try to use this so once this uh image you see in three dimension then you will be able to map this very easily okay either on the digital platform or you can use it by using the tracing sheets and all that okay so this is the co the stereo pair of Corona photograph now the data which we are using now okay and which is very much uh uh like uh uh I would say that it is robust and uh in terms of uh the data quality um and very high resolution and available so the uh in on digital platform okay so this uh of course what you are able to see is slightly um reddish color also in this this is exactly what we have prepared is anaglyph okay we'll come to this and this there is one lab which we have planned and which will uh share the data with you and we will ask you to uh do that um if uh you are having those softwares but at least you will be able to learn that how we are generating this now simply in this image uh you can use the uh the filter glasses and that can help you in generating the uh like 3D on your screen okay so Corona this is the previous one was a Corona and this is CTO set one uh you can buy this uh from nrsc Hyderabad so per scene uh it varies from after and uh the for um after and uh forward and after image um so uh the area which has been covered in one scene uh is around 26 to 30 square kilm resolution is around 2.5 M it has it comes with the studo vision capability and the the photographs which are available orthorectified so these are all advantages what we are having with the uh ctoa data okay and mostly we'll will uh use CET data as well as we will show you some uh um data which is collected by the uh uavs okay so with this uh I end here and uh see you in next next lecture where we will talk about the relief displacement and how we can calculate the um height if we are having um from the single photograph and we are having the principal point and all that so we'll talk in the next lecture okay I hope you enjoyed thank you so [Music] [Music] much [Music]