 Okay, good morning everyone. As we have already made, I am Manjit Bhadakur, Assistant Professor, Department of Geography from Cotton University. So, today in the first session we are going to discuss the basis of GeoJC and Spatial Referencing System. So, this basis of GeoJC and Spatial Referencing System we are going to discuss. The learning objective will be to understand the complexities regarding the shape and size of the art. And to understand the different measurement framework to measure the art, its radius, circumference and all. And the different models, referencing models for our coordinate system. And to understand the use of coordinate system in GIS. So, shape and size of the art, the particular science which actually deals with the shape and size of the art is known as a GeoJC we all know. If you see that the, right from the Greek period, the philosophers, then Greek mathematicians, they try to understand their known art. And some of them, few of them, they had the opinion that the art is a perfect sphere. Prior to that, it was also thought that art was a flat, you know, dislike structure. But the simplest model, if you try to understand, geometrically, the simplest model of the art is a sphere. And which is also used for small scale mapping. Small scale mapping means, if we wish to map large areas. For instance, suppose we wish to map the huge continent or the Indian subcontinent or suppose America or this part of Africa. Then, small scale mapping, we can work with a spherical model of the art which is also known as a orthellic sphere. Why? I am going to explain in my subsequent slides. But the better approximation, we all know that art is not a, you know, perfect sphere. But it's an ellipsoidal shape where we have a polar flattening and the equatorial bulging, right? So, these were the philosophers particularly that ellipsoidal idea of the art, okay? Was given by Isaac Newton in, you know, in 17th century. And he, for the first time, said that this ellipsoid is an oblate ellipsoid. Oblate means where you have a north and south flattening and, you know, east and west bulging. So, this is the oblate sphere. Now, the question will be that whether sphere or ellipsoid, which we are going to consider in GIS. As I have already mentioned, if we are going to consider the spherical art for small scale mapping. Mapping the large areas. Then the average radius of the globe we are going to consider 6371 kilometer. Why it doesn't make any difference if we take a spherical art while mapping the large areas? Because in case of the large areas, that means the small scale mapping, the difference between the polar and equatorial radius is not going to affect our calculation. So, that's why if we wish to. But suppose we are interested to mapping a some part of a sum. Like for instance, this university can pass. Or for instance, suppose a small hamlet. Then the spherical model of the art is not going to be useful. Because in that case, we have to consider the curvature of the art. So, for that we have to go with this ellipsoidal model. Now if you see that here, a is your equatorial radius, b is your polar radius. And your equatorial radius, which is a is 6378.13 kilometer. Whereas your polar radius is 6356.75 kilometer. That means that there is a difference of almost 21.3 to be precise. Between the equatorial radius and polar radius. Because here we are considering the ellipsoidal model of the art. But for a larger use for geodetic survey. We are talking about in terms of mapping. GIS mapping. But if we wish to incorporate the geodetic map. That means the field survey map. Then ellipsoidal, geoidal model of the art is the perfect shape. Which is a very close approximation of the real world. Perfect means a close approximation of the real world. Now this ellipsoid is a reference surface here. If we are going to consider a ellipsoid. Because you see that why we are taking ellipsoid as a close approximation of the art shape. Because see that ellipsoid is also a perfect geometric figure. It has a smooth surface. And here we can do the calculation. But the art is not smooth. There are big mountains like Everest. There are deep trenches like the Mariana trenches. So there is ups and downs. The ellipsoidal model is not going to take care of these anomalies. In terms of the height of the art. But the geodetic model does. So that is why ellipsoidal model is largely used for horizontal positioning. Whereas the geodetic model is used for vertical positioning. Means the ellipsoid will be used for a latitudinal and longitudinal measurement. In the ellipsoidal and geoidal model of the art. Whereas geoid will be considered for your vertical. That means the elevation altitude. Where you are going to get the precise altitude measurements. So this is a perfect model. That means it is a close to the approximation of the art. As a sphere or ellipsoid. Now in case of the ellipsoid. We have to understand that this ellipsoid is actually obtained by rotating. A meridian ellipse about its minor axis. Now we all know that the art axis. Where it rotates actually. Is this one. This is the minor axis. And this axis is also your art spin axis. And this one this is known as a semi minor axis. So the equatorial one is known as a semi major axis. Or major axis if we consider the entire circumference. And this polar one is as a semi minor axis. Or a minor axis. So one part of it is known as a semi. Semi minor and semi major axis. Now this minor axis. Is coincide with the art spin axis. Because art is also spin. The major axis is actually swipe out the equatorial plane. As an ellipse is rotated. So basically this is the idea of Newton. As the art is rotating in its axis. So the basic idea is that due to the centrifugal forces. The east and west. That means the equatorial must be balls out. So this is the idea. Which is also correct. From that you know space observation and all we came to know that yes. This is a perfect or close approximation of the art model. Now moving forward. You see that this ellipsoidal model. Always I am trying to refer it as a ellipsoidal model. Why? Because there are n number of ellipsoids. The ellipsoid is definitely is going to be a global model. That means it is going to make the art. Trying to measure the art axis measurement. That means the semi major and semi minor axis. So if you clearly see that I have just mentioned here few of the official ellipsoids. Now here you clearly see that there are 1, 2, 3, 4, 5 ellipsoids. And if you try to understand that equatorial radius and polar radius. In each of this model. They differ slightly. Because these are modeling. So the most widely used ellipsoidal model of the art is world geologic system 84. WGS 84. And here the equatorial radius is 6378137. Polar one is 6356752. And the measurement for the flattening of the polar areas. Is known as a polar flattening. And how we can achieve it? The polar flattening which is also known as an oblate-ness. Because as I have already mentioned. That this sphere is a oblate sphere. So that oblate-ness can be measured by F. Is equal to A means the your equatorial radius. B means the polar radius and divided by A. Then we are going to get the polar flattening. And this polar flattening is always expressed as a ratio 1 by F. So here you can see these all these models. There is a difference in the polar flattening. Because they are different models based on their approximations. They were created. But most widely used ellipsoidal model is WGS 84. Why? It is a global reference system. And now it is in all our GPS, GNSS. They are using the WGS 84 reference. For arts measurement. Now next question is the data. This is a data means a reference. For measurement on the up surface. So this data is basically nothing but a coordinate system. Which actually provide us the basis for or reference for our measurement. Measuring x, y and z coordinate. That means latitude, longitude and altitude. So there are the data parameters. As I have already mentioned, it is going to deal with the art shape and size. So the major axis, minor axis, their orientation, rotation, you know translation and ellipsoidal height is going to be the reference for the datum. But here we have to see that there are two types of datum actually. One is your horizontal datum and another one is your vertical datum. As I have already mentioned, the horizontal measurements will give us the x and y coordinate. That means the latitude and longitude informations. And the vertical one is going to give us the heights. So this horizontal datum is basically is a collection of specific points on the art that have been identified according to their latitude and longitude. This is horizontal datum. So any datum point you are going to consider. If it is a horizontal datum, it will be based on the latitude and longitude measurements. The vertical datum is a bit tricky concept to understand. Why? Because it is a collection of specific point on the art surface with their known heights above and below mean sea level. Now here is a new concept, the mean sea level. Though we are using in our day to day life the MSL, MSL. But this idea of MSL is a very tricky idea. Because you see whenever I have to say about like mean sea level, suppose the coastal areas. So there the tidal heights we can consider for the mean sea level. But what about the areas where there is no sea? How you are going to get the mean sea level? So to solve that problem, the geodetic scientist has made an art model for us to get the mean sea level at any point on the art surface. And the concept in details can be understood through this particular video. So I would like to request you to please go through this video in YouTube. I have also provided the link here. So this is about the vertical datum which is a bit tricky concept to understand. Now there are another two things we have to deal in which is the geodetic datum and the local geodetic datum. There are two types, more two types of datum. One is geocentric and one is local geodetic datum. Now geocentric datum is actually if we have to say it is a global datum. Because in the geocentric datum it has considered the art center as its origin. So as we are using for instance the WJ-84, it is a global datum. So here we are going to consider the art center as the origin. But in a local datum is a best approximation of the size and shape of a particular part of the art or I mean land or sea surface. So this local datum is actually based on some local measurements. Because you see as I have already mentioned your global datum is not suitable to help you for large scale mapping. That means for the small areas because there we will not be able to understand or get the measurements for the vertical differences that altitudes. Because here the global datum will give you a general that means average elevation globally. But when if you are interested for a small scale mapping where your height meters for suppose a road project or railway project. Where you have to go for art cutting or land filling. In that case 1 meter, 2 meter difference will be a huge difference. For that reason we need these local georetic datum. There are few examples of these local georetic datum like NAID 27, not American datum or European datum or Indian georetic datum. As a Kalyanpur in central India as the point of reference. Kalyanpur datum, it is also known as a popularly Kalyanpur datum. The great trigonometric survey actually use that datum for mapping the Indian subcontinent. So this is the Indian georetic datum for the measurement in the Indian subcontinent. Here if you wish to go for a small scale mapping you only have to understand that you have to get the height information. That means the vertical measurements on the basis of this local datum. For your horizontal measurements it is okay if you are dealing with that global datum. That is WGS 84 will give you also a close approximation. Next after this shape and size, the next concept to understand is a coordinate system. We all are familiar with this coordinate system. This coordinate system is a reference used for representing the location on the geographic features. Basically it is a framework of latitude and longitude. Here the unit of measurement is used for global geographic coordinate system for latitude and longitude. Basically coordinate systems we have two types of coordinate system. One is your geographic and another one is your projected coordinate system. Now we have to deal with this geographic one. Now the geographic coordinate system is a reference system for identifying locations on the curved surface of the earth. This is a geographic coordinate system. Here the location on the earth surface are measured in angular units from the center of the earth relative to the two planes. There are two planes basically while doing the measurements in a geographic coordinate system. Geographic and projected I am dealing with. In case of geographic coordinate system we are talking about two planes for the angular measurements. You see we have two planes. For the measurements we know that latitude and longitude are going to be the x, y coordinates. For the latitudes that means the parallels our plane will be the equatorial plane. The angle formed by a particular line drawing from the center of the earth to the equator any point on the equator. And another line from the center of the earth to any point on the parallel. That angle will be the angular measurement for the parallel. That means as we say the 10 degree north, 10 degree south. That means that particular parallel is forming a 10 degree angle at the center of the earth. So here the plane will be the equator. Now in a second case where for our longitudinal measurements. There our plane will be the prime meridian. So two planes basically we are talking about. So the angle between the prime meridian and the respective longitude will be the angular measurement for longitude measurements. So two planes basically we are dealing with the two planes because these are angular measurements. So this is about the geographic coordinate system. Now what about the projected coordinate system? You see why do we need the projected coordinate system? First question because as I have already mentioned this geographic coordinate system is actually the curvature of the earth. It has taken consideration of the curvature of the earth. But for our day to day measurements, planning, surveying we are going to deal with the two dimensional surface. Now this projected coordinate system actually converted the geographic coordinate system into a two dimensional surface. So that's why we need this. So here the coordinate system will be defined on a flat two dimensional surface. And here the coordinate system has a constant like length, angle, area. So area measurement, length measurement for that we need this two dimensional projection system which is known as a projected coordinate system. The basis is obviously the geographic coordinate system but here we are going to do the calculations. That's why we have converted into a two dimensional surface. Most popular one here is the universal transverse marketers projection, UTM projection. Conformal projection where we can do the measurements accurately. Universal transverse marketers projection and the entire world is divided into some zones. The details is there in your text resource. Please go through it, the universal transverse marketers projection. Now the third one here we have to going to discuss is a planar coordinate system. Basically this is a part of projected coordinate system only. Why it is known as a planar coordinate system? Because here we are going to project the earth on a plane. That means on a two dimensional surface. Now whenever we are trying to project the earth on a two dimensional surface we know that two dimensional surface can touch a single point on the earth surface. Now if the two dimensional surface is touching the polar areas then our planar coordinate system will be polar. If it is touching the equatorial area then it is going to be the equatorial or it can also touch any parallels in between. This particular projection planar coordinate system specifically is also known as azimuthel or zenithel projection. Now if you are suppose in the first figure we know the plane of projection is touching the north pole. Now then this particular projection will be known as polar zenithel projection or polar azimuthel projection. If it is touching the equator then it is going to be a zenithel projection equatorial case or zenithel projection oblique case. If it is touching any parallels in between the equator and the north pole or south pole. Now here another important point is this that this particular projection is normally obtained by using source of light. Whenever you are using the source of light it is based on your perspective that is known as a perspective projection. Now if we have to suppose there is a network of reticles here and we want to project the network of reticles on this particular plane surface. Now light can be placed in different positions. Suppose that this particular surface is a light sensitive surface and we are allowing the shadows to fall on that particular surface and it is taking the imprint and in that way we are going to get the coordinate systems, the network of coordinates. Now there are three possibilities for perspective. The first possibility is that that you can place the light at the center or you can place the light opposite to the plane of projection. So it can be placed at the center or just opposite if it is in a north pole then the light will be placed on the south pole. Or if it is placed equatorial case the opposite side of the equator plane this is one possibility or the light can be placed anywhere in the infinity away. So there are three possibilities. So on the basis of these three possibilities if we place the light at the center that means if our perspective is at center then that particular projection will be nomenical. Then it will be polar zenithal nomenical projection. Now if we are placing the light at opposite of the plane of projection then it will be polar zenithal. This group is known as stereographic then it is going to be stereographic. And last one is your orthographic where we are going to place the light at infinity. So you see on the basis of the placement of the light that means the perspective your projection is going to be different. This is a polar case that's why your parallels are coming as concentric circles and meridians as a straight line. So in case of your poles if it is like this place center or opposite or at infinity all the parallels will be projected as a concentric circle. And the meridians will be straight line radiating from the center. So see on the basis of your perspective the projection is going to be different. Why do we need them? For different use like for stereographic or nomenic there are different use of this group of projection. So that's why we place the perspective at different places. Thank you.