Class Note for RNR 417 at UA
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Date Created: 02/06/15
Under standing Data Conversion Another source of spatial infirmation INTRODUCTION A diseussion ofdata sources foi 618 would be incomplete without addressing existing digital data that ean be convened foi use in a GIS sottwaie environment Data that has been previously automated from analog sources inelude avanety of le formats and structures A large body ofthese digital spatial data formats inelude those known as Federal Geographic Data Products and include fonnats such as VPF DLG TIGER and so on These products are otten available in anational coverage and are automated from relatively small seales DLG data was onginally automated from maps at a seale of 1100k At the loeal and site level it is also eommon to have spatial data available in other formats suitable foi use in CAD computer aided diamng systems These sottwaie applications are especially useful in the development and manipulation ofinformation displayed as electronic diawings They aie quite eommon in the architecture engineen39ng and product design elds Many times information that would be useful in a GIS environment can be obtained from these CAD diawing les This information ineludes location andidenti cation at aminimum The use ofinformation from CAD can require its conversion into a format that can be processed using GIS sottwaie g DEFINTIONS In our discussion of forms of data processing we have focusing on coordinate data transform atlaVlS These ti39ansformations can be involved in simple activities like calibrating a digitizer tablet or more complex projective transformations Data ti39ansformations are defined as a change ofeoordinates in which a function ofnew eoordinates is substituted for eaeh original eoordinate These processes can inelude those that convert eoordinates from one eoordinate system to another through translation scaling skewing and rotation These are ealled affine transformations and they oeeur when a digitizer tablet is ealihrated 821an PoLman A er PoLman Our current topic data eonversion differs in that it involves the translation ofdata from one format to another Simply put it is the eonversion from one my of encoding data to another way Data eonversion ean be eonsidered in two broad categories structure eonversion and format eonversion Struetural eonversion is demonstrated by the forward and backward eonversion from raster to veetor stxuctures Conversion from Vector to raster structure is termed rastenzatxan Conversion from the raster structure to veetors is termed Vectanzazxan Geographic data is otten eonverted between these two structural formats to normalize their representation Seanned map data for example starts out as digital raster and ean end up being veetorized into a feature class Conversion also can be Balm Gnuva MlerGRlDPOlV used to refer to the process of changing features ofa r t s 3 3 z s L gwenstmcture fromone I a I 3 5 t 3 filetypetoanother This 2 2 2 2 t 3 2 t I processrssorneurnes 5 i i r 2 2 2 accomplishedbyimponing 5 5 i r 4 i 2 2 aforeign leformatintoa s s s t 4 t 4 a nativeGISformat Moving s e s l I l 3 a l l a features from a CAD format to a GIS format is a svn eovrut eommon example ofthis type of le format eonversion The process of file format eonversion moves desired features and attributes from one file type to another As sueh it can be anirnportant souree of data for use in a GIS In both format and structure conversion there is no coordinate transformation feature coordinates are preserved in the process Obviously losing coordinate information when converting from one le format to another would be undesirable CASE STUDY THE CONVERSION OF DATA FROM CAD TO GIS As mentioned earlier geographic features stored in a CAD data format can be an important source of digital data for use in a GIS Although the concept is simple enough convert from one le format to another while preserving coordinate information39 the process can involve multiple steps There are several issues that need to be considered when undertaking this type of transformation The rst is to understand the Hm difference in the vector data storage and representation between these two formats CAD and GIS share the use of vector objects but came from different origins at different times CAD data is structured to represent an electronic drawing in a way thatis similar to traditional drafting This is so that the process of dra ing could be emulated in digital environment Practices such as using Mylar overlays to represent different layers of a composite drawing have direct digital analogs in the structure of CAD data Lines text and patterns are stored in the CAD le as elements having visual properties such as line width color and layer From a le structure standpoint the CAD data can best be understood in one ofits many le formats the ASCII exchange format In this format displayed below it can be seen that the vector object geometry coordinates and feature representation are contained in one data record The le is strueturedrn allnear manner wrth the format ofa flag eode then a value For example m the le below the flag 10quot means xrcoordlnate to followquot the ag 20quot means yr eoordnate to followquot and so on Note that there are eodes for the symbolrzaaon ofthe element sueh as eolor and lrnetype Noaee also that thrs type ofrnformaaon ls repeated p2 vertex not per llne 8 Layer ag Layout layer name Layout 6 entlty type ag solld W solld 66 entlty Color ag 1 Color 1quot black 10 399959 ag 34 1 9 69 20 3 1 29 45 3 0 0 0 0 end entlty record Vertex next Vertex To eonyert the elements hnes polygons ete m the CAD flle rnto features m a feature elass wlll requlre an understandmg ofthe strueture of the CAD data It mrght be assumed that the proeess ofeonyerang from CAD to GIS ls a slmple onerstep onercommand proeess 1n faetthe proeess lnvolves yanable numbers of steps dependmg on how mueh ofthe layer and symbolrzatron propemes of the CAD data are to be retatnedrn the GIS feature elass These addaonal steps mrght be neeessary to meet the datamode requrrements m a GIS database The frrst ofthe two gures below ls a sereen grab of CAD data m ths ease belng dlsplayedln rts natrye formatrn AreMap The drawrng has been enlarged to show the detatl ofthe hues and text Both the llnes andthe text are treated as drawlng elements and are storedrn the CAD le wrth therr symbolrzatron parameters In thrs ease the text ls an lndex to the numberedbulldlngs shown m the drawlng The seeondrmage ls the same CAD elements after eonyersron rnto afeature elass Note that the llnes are present andln properrelatron to eaeh other The texthas been redueedto rts geometry an rnseraon pornt Note also m the Table of Contents m the seeond AreMap rmage the presenee of some addtronal tables These tables hold among other thrngs the yrsuahzatron parameters for the llnes andthe stxmgs for the text rnseraon pornts unnued mum mmlmn AEIAI EJJE EdJJ LJew Jnseu SeJechmJ 1sz mm er mqu J x Jt39v Task aaveHewFaamve J J Jmmw EH2EJEBWJEEJ JTnuumvl Juz amJL Jt a J J DHHQJJLEaEXJnm t v amommjgwgv kmamvngm amaz gqMJMOMgiJ JLEJEJr M w mum E g EDH wllh MD Faalma Class E g X may E R5 znnnsERJEs J own I ZEIEIEISERJES J DWE Annma E D ZEIEIEISERJES J DWE F mm AS ANJMAL SHELTER a I mama J own mm 2000 JRRJGATJON WELL 4 20m MACHJNE STORAGE a m ZDDEISEFHES J owe F nJygm 2002 FUELSTORAGE III 2003 DOMESTJC WELL 5 a gtltcJan2nnnsEFJJEs UmpOHUKDr 2004 JU DGJNG RAVJLJONSTORAGE a as 2 2005 MEAT RROGESSJNG LAB 2mg STORAGE 2007 CATTLE EARN 2008 MACHJNE SHOR zany TRAcTOR SHELTER 20m JRRJGATJON LAB 2 EEEO STORANJMALHOLOJNGSHEO 2ng VET SCJENCE LAS 2mm MACHJNE STORAGE 2014 JNGJNERATOR 2015 MACHJNE SHOR 2016A TRAJLER 20168 TRAJLER 2m7 MEAT LAS 2mg ARENA 2mm 2mm JRRJGATJON WELL 2an 2n22 m2 El S 4 D U rwanp m o 00sz 2 anNaAVTTaaAJw mm m2 Szuz quotT DJ pJay Source 82 1 3J53 73 2mg 39 Unknnwn uquot JEJLI e m LEW JnsevJ Jechnn in J Ema v J gt Jim Task Wm JEWJJEED JBBWJ EJEEJWWI mmimmwwf wzu D m waaax lm Zwonw gmwmgv kFJQJD39A39E JQQ 3970 QR51 0MQJ LayevZJEIEISERJESJDWEAnnnJaJJnn39 oan Wm er mm E 5 EDH wllh MD Faalm Elan a a X may a a znnnsERJEs J Dwa D ZEIEIEISERJES J DWE Annma E D ZEIEIEISERJES J DWE F mm E D ZEIEIEISERJES J DWE FnJvJJnE E D ZEIEIEISERJES J DWE F UJygm I x cva g2EEIDEERJES JngpmeJ a mam E I F39mm 53 a H Um I D AJea D EadLayev D Em C TxJF mD away ems R uJe mm um y 3959 u Jags m In fact most of the properties such as layer color linetype etc that were part of each data record in the CAD le are now stored as values in tables One of these tables is shown below Notice that there is an object ID and a series of properties for each text string in the table The entity ID is a foreign key from the point feature class for the text insertion points Wm A2111 omgmlnt mum mu mum mm Dannit 1 23m 537 A5 AS 2 231 m ANIMALSHEUER ANIMALSHEUER 2 232 539 IRRIGAHONWELL IRRIGAHONWELL 2 2 son man man 2 23 5M MACHINESYORAGE MACHINESYORAGE 2 235 m 2mm 2mm 2 235 m FUEL sroRAoE FUEL sroRAoE 2 237 SM 2mm 2cm 2 m 565 oomssncwstt oomssncwstt 2 239 565 2mm 2mm 2 2m 5M 2mm 2mm 2 2M sea JUDGINGPAVIUONSYORAGE JUDGINGPAVIUONSYORAGE 2 m m zuus ms 2 m 55 Man pwocssswe LAB MEN pwocssswe LAB 2 m 551 zuus zuus 2 us 552 sroRAoE sroRAoE 2 us 553 2mm 2mm 2 2w 55 CAYYLEBARN CAYYLEBARN 2o m 555 2mm mm N All 4 Renard LL41 i jg Shaw W Seieeied Renard UnulalSZSSelecled Baum v If it were desirable to have the actual values of the text strings associated with the text insertion points in the feature class it will be necessary to further process these data Since the entity ID is present in the Attributes of T x rop table and the text insertion point feature class it is possible to associate this information by a relational join After joining the T xtProp table into the feature class Jmnlynu EWEM adealalalmlagu saunhulelahlesnymm the feature Class table effec iVSIY now rmWmhahzehwsieamvesmwhdala has all the text property information for each w duwu want In imnlnlhxlava text insertion point The resulting revised quotw mmwm m e 3 feature class table is shown on the following 1 Qumxethelieldmlinlayeythallhemv bebasedun page At this point all of the text properties including the original string values themselves are available as attributes of the point features 2 Chumlhexehieluriunlhiilay21mhadlhslahlelmma nk would make possible for example to Wm 3 El use the T xtProp T xtValue attribute as a source 17 Sme lhu ennim tabla nr lawn n In Im of feature labeling in ArcMap The result of such an operation is displayed below the 3 modi ed feature class table below The text strings are shown as labels for their own insertion points and the drawing is graphically recreated The difference is that information is now in a different format ready for use with other feature classes Awiumnu Data In summary the process ofconverting CAD data for use as a feature class in a GIS is a multistep process The process begins with a thorough examination of the CAD data to gain an understanding of the way it was structured with respect to layers and symbolization The coordinate system of the CAD data will have to be known should it have to be transformed into a system common to other feature classes A er ninning a process to read and import the CAD elements as features and their properties as tables into the GIS environment additional steps are required to reassociate the properties with the features Once this is done the geometries and properties of the former CAD drawing are available for use in GIS software as native forrnat feature classes smne PmmEmIn YnPrnnnhnmln Yleranxlvnlue mm mmmn 1 5511111 257 257 x 2 5511111 255 255 x 3 5511111 259 259 x a 55111 271 271 2511 5 5511111 272 272 x 5 5511111 273 273 x 7 5511111 27a 27a 5 5 5511111 275 275 x 9 5511111 275 275 x 15 5511111 277 277 x 11 5511111 275 275 x 12 5511111 279 279 x 13 5511111 255 255 5 M 551111 251 251 5 15 5511111 252 252 x 15 5511111 253 253 x 17 5511111 25 25 x 15 5511111 255 25s 5 19 551111 1 255 555515 Lg 4111 411 5155 W 52125125 555515 1555151331 551551551 5511515 4n 51 11155111 11 11 5151511 51151 5 1 j mm s f l 1511 l mrmw v 11555 1 139 5 ltemlrtluummlmwm wla 11 T555555 39K El amp g 39MIFEI jDD E H axlnuelw Wail 52j515111r nwwljAvglr d v FquotVO1 I 1Fkon 15 5 1s in 5545735553 E 9 inn with EAI anlule Elan 111mm 5 25 2111551551 15111 L 255595515515575111152 5 E 55595151 5575115111 E WWW 1m RRlGAVl 5 E 55155551551 DWE 511 1115 mm 1W E 5 1d E Wmva 11157551151 qu 1553111555 1 L Fm 5352515 5m 5 5 51551555555515 155515711 5 m WWWDWOW 31 1191 n r 21 J 105 11551555555515555 E E 5 5 r 7 5515 F155 7 quot CANE BARN 51 7 r155 m wa11111 311 u E 215 m 15551559155155 n 355151 2515 1551551151 U5 E 21w 5555155151555055555155 Cl r1911 m12 5 551515 951 5 5E s39okmz m 5111555155 N S 551511111 11 355 155155 E 5125 In 505155 grin 1551551 05 555 mm 5155 39 Aa gt1LU d 121 51 J 1 1 5 221155111155511 2