Troubleshooting GPS Data

Transcription

1 MAP, DATA & GIS LIBRARY Trubleshting GPS Data Intrductin GPS data can appear in a variety f frmats (.txt,.csv,.gpx,.xls,.xlsx,.tab, etc.) and crdinate units resulting in messy data that must be cleaned up befre it can be used in ArcGIS. This dcument attempts t address sme cmmn issues encuntered with GPS data. If the data hasn t been laded frm the GPS, fllw the steps fr getting waypints frm the GPS t GIS using DNRGPS utility. This is the ptimal methd fr pltting GPS data. If the data is already in.gpx frmat, run the cnversin tl GPX t Features in ArcGIS. GPS Data in Degrees, Minutes, Secnds Ideally, latitude/lngitude crdinate pairs are mst useful in decimal degree frmat (hddd.dddd). Hwever, sme cases have data in degrees and decimal minutes r even degrees, minutes and decimal secnds. The data file (.txt r.csv) will be fixed using Micrsft Excel. 1. Run Excel. 2. Select File > Open. Navigate t the lcatin f the text file (if necessary, change the file type t Text Files in rder t see all files f this type. Text Imprt Wizard Step 1: Step 2: Identify the data as delimited (tab r cmma) r fixed width Identify the start imprt at rw click Next Chse delimiter (preview indicates hw yur chice affects the data) Click Next Step 3: Set the data frmat fr each clumn (this can als be dne later, if necessary). Click Finish.

2 P a g e 2 The table appears squished. 3. T expand clumns, click and drag acrss all clumn headers (A thrugh L) t select the affected data. 4. Frm the HOME ribbn and CELLS > Frmat sectin, chse AutFit Clumn Width. In the abve example, Lat/Lng crdinates are fund in clumn E under the name Psitin. This frmat shws bth latitude and lngitude in a single clumn as degrees, minutes and decimal secnds. Unfrtunately, this frmat is unacceptable fr GIS. We will cnvert them t decimal degrees. Cnverting t Decimal Degrees Remve unwanted clumns GPS data smetimes includes a lt f extra data nt pertinent t yur specific study. 1. Identify clumns and/r rws t delete and tidy up the table. 2. When all changes are made, cpy/paste the POSITION clumn s that it is the last ppulated clumn, if necessary. Splitting the Clumn 1. Activate the DATA ribbn. 2. Select the clumn cntaining the crdinate pairs. 3. Frm Data Tls, select Text t Clumns. The 3 step wizard will guide us t split this clumn such that we will be able t calculate decimal degrees. Step 1: select Fixed Width. Click Next. Step 2: Identify breaklines within the clumn. Each piece f the crdinates will need t have separate clumns. Click Next. Step 3: default data frmat is acceptable. Click Finish. 4. The crdinate pairs have been parsed int 8 separate clumns. 5. Save yur wrk in a new Excel wrkbk (.xlsx). Calculating Latitude 1. Enter a new clumn with the name Latitude. 2. Click the cell directly belw and enter the fllwing equatin using crrespnding cells = Degrees + ((Minutes / 60) + (Secnds/ 3600)) HIT ENTER =D2+((E2/60)+(F2/3600)) RESULTS IN

3 P a g e 3 3. Click the cell cntaining the equatin and click/drag the black handle in the lwer right dwn the entire clumn t apply the equatin t the whle clumn. Calculating Lngitude 1. Click the first rw cell f the first vacant clumn and enter the name Latitude. 2. Click the cell directly belw and enter the fllwing equatin using crrespnding cells = -1*(Degrees + ((Minutes / 60) + (Secnds/ 3600))) HIT ENTER =-1*(H2+((I2/60)+(J2/3600))) RESULTS IN Click the cell cntaining the equatin and click/drag the black handle in the lwer right dwn t apply the equatin t the whle clumn. 4. Save the Excel file. Deleting redundant clumns 1. At this pint, the latitude and lngitude clumns are reliant n the 8 clumns we created earlier. If we tried t delete the seemingly meaningless clumns, we wuld lse the calculated values. 2. T make the calculated values permanent, select the 2 clumns, hit Ctrl-C n the keybard r right-click and select Cpy. 3. Highlight tw empty clumns, right-click and frm the paste ptins, chse the secnd ptin called paste values. IT is nw safe t highlight and delete the 8 parsed clumns plus the first 2 calculated lat/lng clumns resulting in a tidy Excel table. 4. Save the Excel file. 5. Save a secnd cpy in CSV frmat t be used in ArcGIS. If prmpted with a warning, click cntinue. 6. Clse all Excel windws befre prceeding. If this sectin was useful, mve n t the instructins fr Pltting X,Y Data in ArcGIS, fund n page 7.

4 P a g e 4 GPS Data in UTM Smetimes GPS data has crdinates described by UTM eastings and nrthings in a single clumn. Befre these crdinates can be pltted, they must be parsed int separate fields. Sample text file with UTM crdinates (this is a very messy file) 1. Run Excel. 2. Select File > Open. Navigate t the lcatin f the text file (if necessary, change the file type t Text Files in rder t see all files f this type. Text Imprt Wizard Step 1: Step 2: Step 3: Identify the data as delimited (tab r cmma) r fixed width Identify the start imprt at rw click Next Chse delimiter (preview indicates hw yur chice affects the data) Click Next Set the data frmat fr each clumn (this can als be dne later, if necessary) Click Finish. The table appears squished. 3. T expand clumns, click and drag acrss all clumn headers (A thrugh L) t select the affected data. 4. Frm the HOME ribbn and CELLS > Frmat sectin, chse AutFit Clumn Width. In the abve example, UTM crdinates are fund in clumn E under the name Psitin. This frmat shws eastings and nrthings in a single clumn. GIS requires they be in separate clumns.

5 P a g e 5 Splitting the Clumn 1. Befre splitting the clumn, it is a gd idea t clean up the table by deleted redundant clumns and rws. 2. Make sure the Psitin clumn has 3 blank clumns t the right where parsed data will be saved. 3. Activate the DATA ribbn. 4. Select the clumn cntaining the UTM crdinates. 5. Frm Data Tls, select Text t Clumns. The 3 step wizard will guide us t split this clumn. Step 1: select Fixed Width. Click Next. Step 2: Identify breaklines within the clumn. Each piece f the crdinates will need t have separate clumns. Click Next. Step 3: default data frmat is acceptable. Click Finish. 6. The crdinate pairs have been parsed int 4 separate clumns. In the example belw, clumns G and H include eastings and nrthings, respectively. Change the name f these clumns accrdingly. 7. Clean up the table by deleting unwanted clumns and rws. 8. Save yur wrk in a new Excel wrkbk (.xlsx). Then save as a CSV file (say YES t prmpt) and clse Excel. 9. Fllw the steps fr Pltting X,Y Data in ArcGIS.

6 P a g e 6 Field data represented by 6 digit UTM references Data gathered in the field using a 6 digit UTM grid reference system must be expanded t reflect mre cmplete UTM crdinate pairs. In a 6 digit grid reference, the first 3 digits represent the easting and the last 3, the nrthing. The 6 digit reference must be split in tw then expanded. Splitting the Clumn 1. Activate the DATA ribbn. 2. Select the clumn cntaining the 6-digit reference. 3. Frm Data Tls, select Text t Clumns. The 3 step wizard will guide us t split this clumn. Step 1: Select Fixed Width. Click Next. Step 2: Identify breaklines within the clumn by clicking between the 3 rd and 4 th character. Click Next. Step 3: Default data frmat is acceptable. Click Finish. 4. The crdinate pairs have been parsed int 2 separate clumns. 5. Save the dcument in Excel (.xlsx) frmat. Befre cntinuing, yu must cnfirm the gegraphic area where the pints were gathered. Refer t a 1:50k tpgraphic map f the area t identify the expanded values f nrthings/eastings, as well as the UTM Grid Zne (Niagara is in 17N). 6. Enter a new clumn title fr Easting. Click in the first cell and enter the fllwing equatin t expand the grid reference (assuming a Niagara lcatin): =CONCATENATE("6",B2,"00") HIT ENTER RESULTS IN Click in the cell where yu entered the equatin and drag the black handle dwn t apply the functin t the rest f the list. 8. Enter a new title fr Nrthing. Click the first cell and enter the fllwing equatin t expand the grid reference: The table shuld lk like this: =CONCATENATE("47",C2,"00") RESULTS IN Save the Excel file and save a secnd cpy in CSV frmat. 10. Clse Excel befre cntinuing with steps t plt X,Y data in ArcGIS. 9

7 P a g e 7 Pltting X,Y Data in ArcGIS It is simple t plt X,Y lcatins if the data table (ideally in CSV frmat) has tw separate fields fr crdinate pairs such as, latitude and lngitude (decimal degrees) r UTM eastings and nrthings. The table may lk similar t this: 1. Run ArcMap. 2. Click Add Data and navigate t the CSV file, select it and click Add. The table appears in the Table f Cntents. NOTE that the file must be clsed in all ther applicatins r yu will receive errr messages. 3. Right-click the table and select Display XY Data 4. In the Add XY Data dialg, specify the fields that cntain the X and Y crdinates, with X crrespnding t lngitude (easting) values and Y crrespnding t latitude (nrthing) values. **TIP: the fllwing table summarizes X, Y frmats.** Latitude 43 degrees UTM-Y 4,763,000 metres N Lngitude -79 degrees UTM-X 623,000 metres E 5. Under Crdinate System f Input Crdinates, click Edit 6. Identify the spatial reference accrding t yur data: Fr Latitude/Lngitude use: Gegraphic Crdinate Systems > Nrth America > NAD 1983 Fr UTM Eastings/Nrthings in mst f Suthern Ontari use: Prjected Crdinate Systems > UTM > NAD 1983 > NAD 1983 UTM Zne 17N 7. Click OK. 8. The Display XY Data dialgue bx is nw cmplete. Click OK. 9. A message bx will appear stating that the table des nt have an Object-ID field. This field will autmatically be created in the next steps. 10. Click OK. The XY data is displayed as pints n the map. 11. This pint data file is called an "event" file. T make a permanent shape file, right-click n the pint data layer and chse Data > Exprt Data. 12. Ensure the Save as type: is shapefile and the lcatin is yur student space. Click Save. 13. Accept the rest f the defaults and click OK. 14. When prmpted t add the exprted data t the map as a layer, click Yes. The layer is nw a permanent shape file including an Object-ID field meaning the data may be used in analysis.