Surveying Prof. Bharat Lohani Department of Civil Engineering Indian Institute of Technology, Kanpur Lecture Module No -02 - 02 Basic Concepts of Surveying okayhellosoweareagain in theanother lecture onbasic surveying andthissis thelecture number two (Refer Slide Time: 00:00:24 min) ofmodule tvvo ourrnodule twoisonbasic concepts ofsurveying (Refer Slide Time: 00:00:30 min) let us go back to the entire structure of the video lecture we have alreadydone our module one we are at the momenttgtalking about module number IWO {Refer Slide Time: 00:00:43 min) in module number two we have already discussedthis particular part in our last lecture so what we were talking in our last lecture lets just recapitulate that we defined the surveying and also we said that how surveying is you know of concerned to the engineers may be mining may be civil any and basically our aim is to measurethe ((geo)) (00:01 :07) information now we saw many examples we started from the building constructions the town planning example of Euro tunnel example of a build example of a road or route alignment and using all those examples we understood that how surveying is useful for an engineer we cannot do surveying or other we cannot do any project without surveying because we need to bring the ground into the laboratory this is what we saw yesterday then only we can work on that ground working is the planning the designing all those effects once the design is complete then what we do we take that design to the ground so again measurementsare involved soweneedto dothatthingsowesawit yesterday thewherethesurveying yis-required then there aretwotypes ofsurveying oneisthesurveying andtheothertaioneypisiii thelaying out surveying isbringing theground intothelaboratory doing theme there inthe groundmakingthemapdoingsomeotherkindsof measurement ofiigeoicinformation andthen bringing it in the laboratory thenonceit isinthelaboratory wehaveworked upon ioiuridesign andplanning otherthings wetakeit outsothatpartwascalled layingoutthenect1what wediscussed wediscussed that surveying is basically aboutthemeasurementsfania iweicannot measure withoutanyreference i gave youalso anexample ofachild pone: earlichild and hisfather was telling methat his childis of thisheight thenhetold:a heforgot heforgot toputtheother hand the reference because child one year icanfti beofthisheight sothereference isrequired wellheis this height he is this tall so the referenceis ve" pmportantin any measurementand we saw that how referenceis important for mea lithe geoinformation we needreference for measuring thegeo information nowwhatis heyyreference reference isamathematically definable system the geo information is on the surface of the earth can we use the geo information as such or rather can we use the earth surface as a reference it is not possible becauseearth surface is not definable we do not know the characteristic of the earth surface we cant put any equation for that so we cannot use the earth surface as such so what was the other thing the other thing was we thought of a surface which is physically adjusting that is equipotential surface or a surface which is always perpendicular to the direction of gravity this surface is also called the level surface or geoid and the physical surface which is the geoid is the mean sea level or the surface of the water body becauseall over the water body there will be equipotential everywhere the potential will be same so the surface of the water body ((makes)) (00:04:16) a surface which we say geoid now we can make use of this geoid again as a reference but we had a problem the problem was the geoid is also not definable mathematically because geoid is basically controlled by the distribution of mass within the surface of within the earth because the mass distribution within earth controls the way the gravity ((factor)) (00:04:41) in all over the earth or the gravity forces becausethe mass distribution within the earth is not constant its not uniform so our geoid surface is again mathematically not definable nevertheless oneimportantthingthatwe sawyesterday thatwasabouttheheightor the elevation in surveying orin anyengineering wemean byheightwelsay apointishigher than theother point provided thewater willflowfrom this point tothispoint sowhen wearetalking ofthegeoid orthelevelsurface aspoint which isonhigher level surface andapointwhich isonlower levelsurface thewater fromthehigher levelsurface will always flow to the lower level surface sowecanmake useofgeoid formeasuringithe height sowhatwedidahlasttime (Refer Slide Time: 00:05:35 min) so i am going to draw the surface of the earth here and the geoid in this let us say like this here in this part it is the surface of the sea may be so what we can do now we can refer the height of point from the geoid so thats the direction of gravity similarly here for this point we can refer the height of this point from the geoid also same thing here ((like that)) (00:06:15) now what we what we are talking we are talking that there is another level surface here equipotential surface there is one more equipotential surface passing through this and i will see that if we put a water droplet here it will ow in this direction becausethis level surface is higher than this level surface so what we say we say this point is higher than this point by this amount so the two points are separated or the difference in elevation between two points is the separation of level surfaces which are passing through those two points so in any engineeringsurveywe usethe geoid for measuringthe elevation well when weare talking about the geoid how about the Xand Ypp 0 yes wecan use ageoid formeasuring the elevation butwhat aboutthe andYthe positions sowhatwedidforthatweconsidered thatforourearth 9 0 0 00 {Refer Slide Time: 00:07:32 min) if we can fit an Ellipsoid this is the an Ellipsoid which is fitting best to the surface of the earth now this is an Ellipsoid for which we knew the mathematical equation and what we can do we can project our points on the Ellipsoid so now the distance between these two points is actually the distance (( )) (00:07:56) in the Ellipsoid we know the equation of the Ellipsoid so we know the characteristics of the Ellipsoid so we can use the Ellipsoid for measuring X and Y now another thing why we need a reference as you know that the Mount Everest is the highest mountain in the world how come why not the Alps becauseboth of these have been measured using the same reference if both of these are measured using different references we cannot compare these two so the Mount Everest is somewhere in one part of the world while the Alps are in other part of the world so in order to in order to compare these two we need one single reference which is passing through both of them and then only we can compare the elevations of these two or the heights of these two so for this purpose we need one reference system well we aretalking that our referencesystemis Ellipsoid ((is)) (00:09:00)here and anytwodistances thatwearemeasuring between points Aand forexample: point Bhere isthedistance along thecurvature butof course thedistance between thepointA andB should bemeasured considering thecurvature oftheearth because how physically they arebutthisistrueonlyif wearetalking about avery large eiitentiilarge area thisisnottrueif the area is very small so for our engineeringsurveysbecausein case"of the engineeringsurveysour area ((marginally)) (00:09:34) is smaller youknow anengineering project forexample letus see (Refer Slide Time: 00:09:41 min) if it is in twenty kilometre by twenty kilometre then the separation of geoid or the Ellipsoid or the curvature of the earth form an horizontal plane plane in twenty kilometre is only ten mm i am sorry not this way but this this represents means the distance in the length of the chord and the length of the arc is only for twenty kilometre the difference is only ten mm what is the meaning of this the meaning of this is when we are doing using surveying or when we are doing the surveying for a small area we need not to consider the curvature why should we measurealong the curvature we can rather even if you are measuring along the curvature becausethe distance which we are measuring on the ground we can measure the distance by making a line which is horizontal and we measure this distance along the horizontal what we are doing we are not consideringthe curvatureof the earthratherthe other way we are consideringour earthto be flat so for small areas like this we can consider our earth to be at and we can easily carry out the surveying so at means in that caseour reference plane (Refer Slide Time: 00:11:13 min) for X and Y will be like this X and Y while the Z are being measured from geoid i will give one more example (Refer Slide Time: 00:11:29 min} here istheearth asyousee (())(00:11:35) surface oftheearth and thissurface here isthe geoid andhere istheoodplane which istangential tothegeoids atthisplane nowin thisexample whatweareseeing if weplotourpointletssayor ratherwemeasure the height of the point there isapoint Aandapoint Bfromdeflect plane; orthehorizontal plane byprojecting these points here wemeasure thisheight asatthemoment whatwehave seen these twovalues sowhat weseeinthis case theheight ofAismore than height ofBfrom the datum what isthemeaningof thisthemeaning ofthisisinthiscase thewater should flow from Afrom AtoBbecause weareconsidering theearth tobeflatwearenotmeasuring elevations from geoid; rather wearemeasuring theelevations from aflatplane orahorizontal plane in thatcasethe water should flowfromA toB wellletslookatthegeoid orthelower surfaces equipotential surfaces the equipotential surfaces in this case passing from A will be again parallel to the geoid so we can draw it like this and also from B passing from B will be like this well what we observe onething very interesting if you are looking at the equipotential surfaces in that case the equipotential surface or the level surface which is passing through B is higher than the equipotential surface from A what is the meaning of that the meaning of this is the water will actually flow from B to A not from A to B what is the case here so {wha} (00:14:09) what do we mean by this we mean by this is if we are taking horizontal plane for measuring elevation our elevations will be wrong it might happen that we are giving the elevation to a point as here in this case A more than to a point B this height the water owing from B to A so we must always measure the elevations from the geoid not from the horizontal plane it is said that in all our engineering surveys we can consider our earth (Refer Slide Time: 00:14:47 min) flatforXand YbutforZwemust measure: from geoid sothisisanimportant concernrwe should keep thatinmindsothisiswhatcalled wehave discussed lasttimethese arespimportant concept thatswhyi wanted torepeat these what welldotoday wellstartourdiscussion withsome principles ofsurveying (Refer Slide Time: 00:15:13 min) nowwhat isthemeaning ofthistheprinciples ofsurveying imeansithere aresome things whichweshould keepin ourmindalways whenever we doingsurveying andin orderto explain allthose things whati willdoi willgiveyouangexample andwellstartwiththat example the example is let us say (Refer Slide Time: 00:15:40 min) there is a field an area a terrain and in this terrain it may be of any size there in the ground there are some rivers here okay there are some houses lets say there are some houses here there are some route as Well okay we have got some more trees this is any you know any terrain could be like this while here is the river or a small rivulet you can just think of any area in your surrounding just think of that area our job is we want to make a map for this area so while we are going through this process of making map for this area well go through many things which are very important and very basic for the surveying now what those things are well number one when this job is given to you i ask you okay go to the field and make a map and i give you let us say a tape tape means something with which you can measureand the length of this is thirty metre okay a tapehavingthirty metrelength i give you that tapeand i ask you to makeafmapof this area againto simplify the matterlet us saythis areais of aroundhundredmetreby sixty metre in height okay soit tellsyouabouttheextend nowyoucanvisualize anyarea anygarden in your surrounding andyouaregiven atape andyouareasked tomakfe amap what willyoudo nowthenumber onething which youwould liketodoyouliketogotothatarea observe it rather you justhave anidea okay what kind ofmyarea isorshould what kind oftechniques should i useformysurveying cani useVery goodinstrument should i useverygood instrument that kind ofstuff and can i reachteach andevery point inmyarea isevery point accessible or not so that part the very first part {Refer Slide Time: 00: 18:0p2smin) which we do is called reconnaissance reconnaissance survey and sometimes that is also referred as Recy so so you go into the area you do this Recy by doing this Recy what you try to do well you try to have an idea of the area now once you have done the Recy the second thing that comes into picture is you establish a control network well talk about it what the control network is okay what is the meaning of control network here control network means something which will control your entire survey now ill i will tell you how we will do it here in this case let us say for the same area i am drawing it here (( )) (00:19:01) again you[Noise] sorry youdecide thatbecause youhave given youaregivenonly aitape ofthirty metre length andyouhave tomake amapofthisarea it isnotthat startfrommeasuring individual tree okay the distance between two trees the distance between two hous or example in this area how will you make the map it isnotthatyoustartmeasuring thedifferences lik th between thetrees between therivers between these trees from tree to the riyver-fro tree to the boundarytheseindividual measurements nofirstyouhavetoestablish;ntrolnetwork wellthecontrol network could belet srrosayithat youestablish acontrol network hereanother pointhere another pointhere ;:point here onemore pointhere i amconsidering herethat" sible for us to measure distance across the river using the tapejustasmallriver acan doit okay now what bydo t t what youhave done your network willlooklikeanetwork oftriangle will explainti letussaynatuallnetwork youwillunderstand verysoon theutilityofthisyoudecide about it this network is also decided at this stage of reconnaissance you decide about those points which will become your control point now why we want to do it we want to do it becauseby establishing these some points and measuring the distance between these points very accurately what we can do we can take this skeleton of the area in the laboratory now what is the meaning of that once you have you have gone into the ground you can do this measurementseasily isnt becauseyou have got the tape you spread the tape and measure these distances the only thing is keep your tape horizontal because we consider our earth to be a small area to be at so by keeping the tape horizontally between these two points i can measureall these distances L one L two L three and similarly so all these measurementsare known to you well bringing the skeleton of the area into the laboratory how do we do it how do we plot that well we do it let us say we have a sheet of paper here and we want to make our map (Refer Slide Time: 00:21 :38 min) inthissheet allright wewill letssaywhatA ourVery firstpoint theVery firstpoint forexample 0 sowhat wedoinour:i;sheetwell locate this Ajustarbitrarily A now from Apweiknowiitas wehad observed inthe ground that wehave lines going this way okay so what we do we draw a line L three and L two and again from this point we take an are from A ((thats)) (00:22:17) the Very first line is drawn here Lone we can measure the angle also i am not talking about the angle now and from here we can take the arc of ((just)) (00:22:33) two length so this point is fix similarly as per the triangulation figure there well draw the rest of the triangulation figure what you have done just by the measurementsof these lengths there in the field you are able to draw the skeleton on to the sheet okay so the skeleton of the ground is here on the sheet is on the map so what what we learned from this we learned one thing one principle here that is establishing control network okay so in the caseof the principle (Refer Slide Time: 00:23: 17 min) theprinciplewhatwe learnedhereis controlnetworkalwaysbeforewe beginour surveywe should establish acontrol network andthecontrol network controls oursurvey wewill seein a moment how nowin ourareawhatwewanttodowewantto measure theindividual thingssoto measure theindividual things whati candonowfromanytreei candropaperpendicular here isnt sowhat i know along thislength acertain X thedistance ofatreeisYokay sowhati willdoiwilldoithesame thingherealong thisatacertain length X wehave the distance Y andatithat Ywehave atreesowhat wehave done wehave nowplotted onetree similarly i can{plottheothertreesalsofor example letssayfor thishouse i takethe measurements of thishouse fromthislinebydrawing aperpendicular i measure thisX i measure this Y by measuring this X and by measuring this Y what i can do in my map there is the X and here is the Y and we know there is a house here so what i have done i have plotted the house also so now you will start realising the significance of the control network now some principles which we must follow and we must keep in our mind always one principle we will see is working from whole to part it is very important principle working from whole to part what is the meaning of this the meaning is as we saw also here what we did first we map the skeleton of the area the meaning is first we map these distances we didnt go to the individual features we didnt start measurementsfrom individual features individual trees rather we mapped our area first in a big way we measured these distances very accurately the L one L two L three L four L five all these we measured them very very accurately and then we plotted them here we brought the skeleton of the ground here on our map okay so this is you know what we did we are working first in the whole the skeleton of the area we are bringing at here we are not botheredat that stageaboutthe featuresbut in the secondstagenow working from wholetopartnowwemake useofthecontrol network these triangulationwfigures andthenwe start plotting each and every detail now what is the advantageof this why should we do it now forthisprinciple ofworking from whole topartiifadvantage isaccuracy why now you youtakeit likethisseeourfirstcontrol network yjelltriangulation figure wemeasured that veryaccurately andwemade useofthatinord forfplotting soourthese stations or these survey stationsypyvilrarelbcgtransferred hereveryaccurately because we tookatmost care inmeasurement o le _ now after that even if we are s he:-eleft in measuringthis Y it doesntmatterbecauseit ' iiofthishouse because these twoaretwodifferent things soplotofthehouse or ybeplotofany other tree here if weareplotting bymeasuring the distance here an;:fth1s=d_1srtance sowecansayX here andYhere lo thistreeagainthisoneindependent plot sothisparticular plot it doesnt affectatalltheefseacicuracy of thisplot so by this we made this (( )) (00:27:50) wrong in measuring this so it is not going to affect the entire you know the rest of the map so our errors are not going to accumulate they are not going to add up while if i start doing the mapping lets say i start doing from part to whole in doing it from part to whole what is the meaning i measure the distance between these two trees i measure the distance between these two trees now i measurethe distance from here to the river from here to the river you know what i am doing any little error which i introduce in measuring the distance will be accumulated in all the measurementswhich i follow later on okay so in working from whole to part we maintain the accuracy we restrict our surveys with the certain accuracy so this is very important thing i can give you some more examples of this working from whole to part and this examples are from our daily life now one example could be lets see the timetable it doesnt have to do anything with the surveying but to understand the concept of working from whole to part thetimetable means letussayforthislecture i wasgiven atimeofonehour _ i sowhati havebeengiveni havebeengivenokayyouhave got: me;gir1of onehoursixty minutes and i have to plan my lecture in this sixty minutes sowhati dowelli havegotsixtyminutes nowi planm ' artiofthelecture second part of thelecture thirdpartof thelecture i planwithinthisisixtlminutes onlyit is notthati am goingto youknowgooverthesixtyminutesybe; §G:.*i knowmyboundaries i knowthe wholehadit been theotherwise i havenotbeen iiany timewhati woulddo third partfourth partwithout i willplan myfirstpart ofthelecture of thelecture knowing my boundariesi might sp' sothatstheidea thatsthe many things wedowhere uknowweshould understand because inourlifealso thisprinciple ofworking from whole topart if key [avetalked about oneprinciple thatisveryimportant andthe control networkis atp t ofthatthatisworking fromwhole topart wediscussediolne more principle thatisthereconnaissance observing thearea before hand thenextprinciple nowhereitselfif oneof because whatwehavedonewehavetakenutmost care and we measuredthese length what if some of this length are measuredwith errors what will happen in that caselet us say this L three when we measuredit on the ground we measuredit with some errors what will it do if you measure it with some errors it will distorted my skeleton of the area all the measurementslater on which i carried out will have some error now my map will be distorted so what should we do how can we avoid this kind of thing to avoid this kind of thing there are IWOways number one (Refer Slide Time: 00:31:03 min) wesayredundancy inmeasurement whatisthemeaning ofthat'the__meaning ofthatisif you aremeasuring a length L threeweshould measure it a"numberof timesyoumeasure this lengthfrom hereto herenumberonetime secondtime,maybe from this way maybe third time fourth time sowhat youaredoing youaretaking numberlofyiiimeasurements forthesame length why because maybeoneof themeasurement iswrong theothermeasurement istheredundant measurement but i am surethat your finalvalue whichwill get asthe averageof sigmal3i andnumberof themeasurements Whatnumberof measurements youhavedone so if you are taking the averageof all thesemeasurements which you have carried out for measuring L threeyourlvalue is moreaccurate youaremoreconfident aboutyourvalues thantakinga singlemeasurement soweshould always keepinourmindthatweshould haveredundancy in ourmeasurement Whenever We are doing the surveying whenever we are doing any measurement the second one (Refer Slide Time: 00:32:22 min) thesecond oneisnowhere onlywecarried outallthese lengthwe plotted them here is thereanyotherwayonewayis theredundancy weintroducge redundancy butis thereany other way of checkingthe accuracyof this systemVatit - ~ wellonemoremethod ispossible andthatmethod iswesaycheck line now what isthischeck linehere inthisdiagram hadiwe also measured there intheground let ussaythisline if if whatwearedoing wearenot thislinewhich i saycapital L forplotting my triangulation figure unless using it forthepurpose i amusing thischeck linelater on once i have plotted mynetworkihere okay allthese points areplotted then i check the distance between thispoint and thispoint inthenetwork and i compare itwiththecheck line which i hadmeasured thefieldif mysurvey iscorrect if myskeleton iscorrect accurate thenthemeasured linehereinthemapshould besame asthelinewhich wasmeasured inthe fieldif it is notsothenwesuspect thereis someerrorin ourskeleton so always we can have either one or more number of control check lines in our survey so we should always go for the check line so now you understand what is the purpose of the check line so that we can check the accuracy of our work later on okay now having said this now we will talk about some more principles which we should keep in mind whenever we are doing in the surveying well next next thing comes to our mind is about plotting of the survey becauseso far we were just saying that we have made a map but there are some things some important points which are involved which you should keep in mind whenever you are doing the plotting what those things are here in this plot before you make the plot see the ground look at the ground file it was hundred metre by sixty metre huge area and what you are trying to do you are trying to bring that into a sheet in the in the (( )) (00:34:59) drawing sheets okay its very very small than the actual ground so how to bring that ground into the sheet well you know the answer i believe you have to talk abouta thing called scalea scalemeanswe want to convertthe distanceswhichare large than the ground into the smaller distances for here in the map nowaboutthisscaling whatarethescales whataretheirtypesinumber onewayof representing the scale is (Refer Slide Time: 00:35:35 min) by representative fractionwhatis thiswewritethisrepresentative fractionalsoit is referred as RF as one is to n also many times you can write it as one by n what is the meaning of this the meaning of this is one unit on map is equal to 11units on ground well let us ((say it)) (00:36:18) if our map scale is one is to one thousand the meaning is one centimetre on the map is equal to one thousand centimetres on the ground so a distance which is one thousand centimetres there in the ground we are representing here in our map by one centimetre so this is how {we W} (00:36:43) we represent the scale there is one more way of representing the scale which is called (Refer Slide Time: 00:36:49 min) engineers scale what is this in case of the engineersscale we represent it as such for example let us saywe write one centimetreis equalto fifty metre what isthemeaning ofthis this istheanother vvay ofwriting thescale itsthesame thing in factitsthesame thing aswerepresented butthisistheanother way wewrite it down i if now here inthis case again the if isfiftymetre there intheground isequivalent toone centimetre here onthepvvshatiyou can doyoucan easily findtherepresentative fraction forthis one bynand compute what willbethe value ofnhow can you compute you justC0I1V¬1"t thissiéiilsdiiiiincentimetre one centimetre isequal tofiftymetre okay multiplied by letssayi write incentimetre hundred centimetre soone isequal tofivezero zero zero tothe valueof an five thousandhere so we can convert the scales like this we can convert the RF into the engineers scale and vice versa there is one more way of writing this scale (Refer Slide Time: 00:38:17 min) that iscalled thegraphical scale wellwhat isthegraphical scale graphical scale isif youare making amap likethisthisisthemap and inthismap wehave plotted some details whatever these things areokay ii sothere onthemapitselfwhatwedoweplotourgraphical scale nowwhatisthemeaning of thisthemeaning ishere inourmap wesay okayhp iii wemake alineand onthislinewewriteifor example zero here hundred metre zero metre again hundred metre twohundredand three hundred metre further wedivide thisfirst oneintenparts soeach ofthisistenmetre nowwhat isthemeaning ofthiswhat weare doing wearewriting onascaleaon ourmap nowanydistance between these twopoints if i can measure thisdistance what i candoi canbring thisdistance here if i keep thedistance here forexample thisway-isnt whati havedonei havebrought thisdistance andkeptit here soyoucanmeasure thedistance between thistwotob onehundred metre plusonetwothree four five hundred fifty metre see graphical scale is nothing but a graphical way of showing your scale becausehere in this case the distance is two centimetre so what we have done two centimetre is equal to hundred metre so we can write the corresponding engineers scale also we can write the corresponding RF also so the only difference in this case is that we are showing the scale by drawing a line on the map itself now what are the advantagesof this one very big advantage of this is for example let us say an engineers scale is given to you for this map and there is no graphical scale it is just their map without having any graphical scale and the scale of the map is given only by engineers scale well after some time the map is made today and after lets say ten years twenty years or so the map has got shrunk or maybe it has expanded because ((its a)) (00:41:20) paper or whatever the material there may be with moisture weak time and all that it may shrunk or expand if it is so what will happen if this map has shrunk the distance betweenythese two points which wasearlier atnowbecause it hasshrunk willnotremain anymoreTiX rather it willbe minus delta X now if that is the caseandnow if you useyour engineerssee in orderto determinethe distance between these twopoints thereintheground using so whatyou will do you will usenot X you will mea reghe distancebetweenthesetwo pointsatX minusdeltaX youwill applytheengineers;leor therepresentative fractionon this distance sowhatwillhappen youwillcompute a iiancgygp whichiswrong because there intheground thedistance is notX minusdelta minusdeltaX multipliedby scaleno ?her;the distance is X multiplied by thescalenotX is not this is wrongthis is correctbut we will do it likethisbecause what wearemeasuriing onthemap isonlyX minus delta X wedidnotknow whatwastheX unless we wellif youhave ya x there now points we heamount of theshrinkage gal scale onthemap what what iswhat isgoing what ishappening is*the amount oftheshrinkage which hasoccurred between these two thesame shrinkage istaking place inthegraphical scale also sointhegraphical scale it also shrink bythesame amount sowhat wecan doeven if youare measuring X minus delta X well measure it here because this scale has also shrunk by the same amount the distance which will compute between these two points there in the ground will be the same distance is equal to this so that is one big advantage of the graphical scale well some more aspects when we are talking about this map plotting of the map there is one more important thing that comes into the picture and that is we say plotting accuracy (Refer Slide Time: 00:43:45 min) what isthemeaning ofthisinyour map thebest thatyoucan M (Refer Slide Time: 00:44:00 min) is lets say a dot and the size of the dot generally if you are going to be very very careful the size of the dot is zero point two five millimetre using the best possible plotting pen you can draw a dot of zero point two five mm diameter or even if we can say a line the thickness of the line is zero point two five mm what is the meaning of this does it convey anything yes well when we are talking about the plotting accuracy there is a dot and the size of this dot is zero point two five mm on the map what it is equivalent to there in the ground well it will it will be equivalent to if you are writing the scale S one by n let us say okay the n could be any number for example (( )) (00:45:04) one by hundred what is the meaning of this a dot of this size there in the ground will be equivalent to zero point two five mm millimetre multiplied by hundred isnt so what is this what is the meaning of this there in the ground if there are two objects let me tell you one object here in the ground and then another object if the distance between these two objects in the ground is let suggest particular value is we write it as A and the distance between these two is B if B is less than A what is the meaning of this if B is less than A even if we are measuringthis B in the groundcanwe plot thesetwo objectsseparatelyon one map once i amplotting themap i plotmyfirstobject where i plotmynext plot mynext object i cannot gohere because thedistance between these twoiswithrithiS1ii}1iine itself somynext object willbealso plotted likethistogether isnt soivwhat imean tosay i mean to saytheplotting accuracy isveryimportant it depend depends typo scale depending upon thescale there willbeacertain value there intheground particular value depending what the scale is this particular value will change here sowhatever isthismultiplication theA valu are smaller than the size we cannot sho pin theground if theobject orthefeature v1;hem5¥here in themapokayor if theseparation between twoobjects aswesawherei"slessg hantheplotting accuracy hereintheground we cannot show these twoobjects separathere inthemap soweshould always keep inou adthat towhat extent weshould goand map thisisvery important this plottingveaaccuerac should be measured very accurately in the ground as in the previous examples " (Refer Slide Time: 00:47:33 min) (())(00:47:35) wemeasure these twoobjects thedistance iSiB~schould wemeasure these two objects ascaptured object there intheground orvshouldiwe measure them asonewellthe decision is to betakenbyyourplottingaccuracy?vi- what your plotting accuracy what your scaleis because what youdoyoucompute multiplied byyour scale and any distance any object separations there intheground which isless than thisValue should notbemeasuredt because wearenotable toplotit wewillbeable to plotthethings which are morethanonly sothisisvery important weishould always keep inourmind that what information weshould measure inthisfieldvthatisevgcvoentrolled bythescale okay having seen allthese you know what wehave wehave seen sofarwehave seen some principles ofsurveying forexample in anymapping exercise wemustdothereconnaissance number onenumber twoweshould establish a controlnetwork because wewantto work always from whole to part and then we fix the control network in our area first we i gave you the way we can do it by triangulation well see it later on that we can do it by many methods we establish the control network we measured it very accurately so what its skeleton is fixed we bring this skeleton into the laboratory plot it now you work in part we measurethe individual object okay and then while we are doing the plotting we need to see about the scale what a scale is to be chosen well one more question here how to decide about the scale can you think of some point well the scale will be decided by number one (Refer Slide Time: 00:49:27 min) size ofthearea if there isanarea forexample tenkilometre bytenkilometre and you have plotting sheet ofletussay fiftycentimetrerby centimetre istheplotting area sowhat willbethescale you know yyouycaiinffiind thescale butthis isnotthe only criteria by which wedecide itsize oftheareamanyttimes itssignificance what isthe meaning ofsignificanceiof work when you want togoforhigher scale when you want togoforlower scale sometimes youwant togoforhigher scale youwant toplotit one istohundred sometimes youwanttoplotit oneistohundred thousand when youwantsegtotyploti it oneistohundred thousand themeaning isyouwanttoplotamapof entire state ofentire country okay for example fortheentireUttarPradesh youwantto showin onemapsowellgofor a scale like this because plotting at ((this)) (00:50:38) scale we can bring the entire state in our plotting area plotting area is generally a drawing sheet or may be slightly larger than that so the entire state come in that and here in this case if we are talking about this scale what we are interested in we are interested in a synoptic view of the area not in the details becauseyou dont expect to see individual houses individual roads individual trees at this scale but if you want to have a very very detailed map you want to see the individual tree individual building their room everything you need to go for a scale like this now out of these to this scale is called large while this scale is called small we must keep in mind the value of because (( )) (00:51:32) we are writing the scale the scale is written as {Refer Slide Time: 00:51 :36 min) Sone bynsodepending thisvalue of,S scale issaid tobeeither large orsmall if Sis large it islarge if Sissmall it is,.ys_maly1iiso weshould know thatwhen wesaythescale tobe large when wesay thescale tobesmall inlarge scale and inthesmall scale theamount ofthe information willbedifferentokayi A now something aboutebecausie {ifwe} (00:52:08) ifweare doing some kind ofrepetition you know after talking the scale wetalked about theplotting accuracy how plottingVpiii{iaccu (00:52:14) accuracy isimportant because wecan decide what level of information is to be capturedin the groundis to be measuredtherein the groundit is decided by the plotting accuracy or its scale so we should know this thing we should be aware then the other thing whenever we are doing any measurementswe must do the measurements by some redundancy we should have redundant measurements then the other thing we should always have the check line because we want to ensure after doing our work we can extract our work the accuracy of our work so we must have the check lines in our work so these are all important principles of surveying we should always keep in our mind whenever we are doing any job now finally how we plot the details some little bit about it this is Very simple (Refer Slide Time: 00:53:02 min) plotting of details howdoweplotthedetailsaswearedoinginijthelmap alsowesawit herein (( )) (00:53:15) we plotted some of the details what wedidinthatcase forexample forthistree wemeasured thedistance from thispoint to thispointX andthenfromhere _,we drewa perpendicular andwemeasured alongthe perpendicular thedistance making useofthese twowecanplotthescale similarly therearemanyfways inwhichwecanplotthedetails nowwhatwhatthese ways areforexample letussayif wehave alineweknowthistwo pointsA andB)ajthirdpointC canbeplotted bydropping aperpendicular andmeasuring this X aswedidintheearliercasesothisis calledanoffset while the X offset is Y while the X is called chainage we will talk about it later also so at this stage we have an offset of Y and at that point we have a tree this is how we can plot the tree well the other one now on the same point A and B we can plot a third point now by many ways you can measureeither both the angles this point will ((fix)) (00:54:40) we can measureone angle and one length this point will (( )) (00:54:45) okay we can measure both the length this length and as well as this length this point will (( )) (00:54:49) or we can go in the polar way for example from this point you can plot many points now by measuring all these lengths and all these angles so all these details can be safe so you can you can just know that how can we make use of simple geometry for plotting the things in the field we will talk about these things more later on finally a little bit about {Refer Slide Time: 00:55:21 min) classification ofsurvey youshould look inyour book about thisbecause thisisnothing very important about howweclassify theippisurveiy wehaveseen already plane when we(( )) (00:55:41) reect or Geodetic the another classification is as per the areafor whatkind of areawe aredoingthe classification is thisa townviisgithiis a villageanagriculture areasowedotheclassification based on area alsowecandotheclassification based onequipments whatequipment weareusing areweusing tapechain compass Chevrolet totalstations GPS as well see later on so we can classify our survey this way also then we can classify using the methods the techniques the meaning is are we using triangulation or we are using this traverse we will talk about all these things later on or we are using any other methods for {classi} (00:56:47) for doing our surveying so our surveying can be classified by all these various categories and one more classification is possible which we say by the function or the use who is using the survey who is doing it is this a military survey is this an agricultural survey is this an hydra graphic survey you know who is the organisation who is doing that survey and what is the purpose for the survey may be some mining survey or is this a survey for any geographers so depending those the functionality for which we are doing the survey so we can classify our survey this is not very important not very important concept is involved in this so i would i would like you to go through your book the textbook and read about it so i will finish my this video lecture here and will continue our discussions in the next video lecture thank you very much