Welcome to GIS Jam 2013 at the Alaska Surveying & Mapping Conference, Anchorage.

Transcription

1 Welcome to GIS Jam 2013 at the Alaska Surveying & Mapping Conference, Anchorage. 1

2 In this session we will cover the four basic types of temporal data, how to best prepare data for temporal animations and analyses, functions for working with date/time fields, visualization of temporal data, analysis of temporal data, and some relatively new geoprocessing tools for processing temporal data 2

3 There are five basic types of temporal data: discrete events, dynamic (moving events), stationary events, change events, and rasters from different time periods. 3

4 A date/time field is critical for some temporal animations and analyses. Always index your date/time field in a geodatatabase. It is best to keep all your temporal data in standard GPS time format instead of local time. 4

5 Lets get started with an example of discrete temporal events all the lightning strikes in Alaska from last June. 5

6 The lightning strike data originally were downloaded as a point shapefile the first step was to process the points so they had an indexed date/time field in a geodatabase. 6

7 The StrikeTime field was originally a text field in a shapefile here we use the Convert Time Field to convert it to a Date field type and store the values in the field named StrikeDay 7

8 We index our date/time fields using the Add Attribute Index geoprocessing tool. 8

9 Typically you wil use a date field to control your temporal layer here we will animate the lightning strikes on a daily basis, starting on June 1, 2012, ending on June 29,

10 You can control the appearance of the dynamic date text that changes as the time changes in the animation 01 June, 2012, 02June, 2012,29June

11 You can also offset time to show lightning from June 5 and June 6 simultaneously on an hourly time step. 11

12 With a lag of 1 day, you can show the typical buildup of lightning activity, peaking in late afternoon 12

13 The VB Date Functions are handy for extracting information like day of year, day of week, hours, minutes or seconds of some temporal event. Or you alternatively can use Python scripting with the datetime module 13

14 Using the field calculator and the VB datepart function, we extract from the StrikeDate_Time field ten pieces of information ranging from Year to Seconds of each lightning strike. 14

15 After calculating the stringday field as a function of the Day_of_Week value, you can create a frequency table summarizing June2012 strikes by day of week. 15

16 After calculating new fields, you can easily summarize events in terms of percent occurrence on an hour basis or on a day basis In this example, most of the lightning strikes occurred betwee 1400 and 1900, and day of year 157 was a high lightning activity day with 4120 strikes on that day. 16

17 Next a dyanmic event example moving points these could be radio collared animals, snowmachine travel, mushing, cars, planes, boats, hikers, etc. The typicall example is a GPS location recorded at a fixed interval..in this example every hour. 17

18 Here we have our GPS points recorded every hour starting on Feb 19 at 12:40:16, we enable temporal animation by setting out time step 1 hour and the time extent ranging from our first to last location. 18

19 You can copy the point layer and make the second layer 90 percent transparent, and display that layer cumulatively in the temporal animation that helps show the user the track of where your previous locations were 19

20 Stationary events are commonly sensor events traffic counts, weather station sensor data, etc. In this example, we will temporally animate a stream gauging station with stream discharge data 20

21 We start with an excell spreadsheeet containg date and stream flow in liters per second. Step 1) Use the Copy Rows tool to output the table to our geodatabase. Step 2) Index the date field using the Add Attribute Index geoprocessing tool 21

22 We have a geodatabase with a point defining the gauging station location and our stream discharge table. We have a key field (Point ID and SiteID) to link these table to the point location.. 22

23 The Make Query Table tool links together the table with the point location and then we can use the output layer as a temporal layer 23

24 Here we animate the variation in stream discharge using proportional circles high discharge in late May due to snow melt, Low discharge in early August following weeks of drought. 24

25 The last type of temporal data I am going to cover is temporal rasters. Typically rasters do not contain a date/time field but if you import them into a raster catalog, you can create a date/time field in the raster catalog table. 25

26 Here we use the Field Calculator to populate a Date field with a constant date of 15July

27 Next we use the Field Calculator and the VB DateAdd function to add a year*inffld to each record So each raster has the appropriate year in the flddate. (The rasters are Alaska mean July temperature from 2000 to 2009) 27

28 The temporal animation shows each July mean temperature..there is a wide variation between July 2003 (cool July) And July 2004 (warm July) for example. You can easily export the animation for use in a powerpoint slide show or To post on a website or to post to youtube. 28

29 There are some relatively new geoprocessing tools for working with temporal data. 29

30 The Match Photos to Row By Time tool is useful to match digital photos that have a time stamp To features that have a date/time field. 30

31 Convert time zone allows you to easily convert all your data from local time (digital photos for example) to GPS time. 31

32 If you have point data with GPS time and you want to compute the time between point locations, you need the end time in each row. 32

33 Once you have the End_Time, you can use the Field Calculator with the VB DateDiff funciton to compute the travel time in minutes, hours, seconds or even centuries 33

34 How do you compute the distance between GPS points? Step 1) Add the X,Y coordinates to your point attribut table.. 34

35 Step 2) Add a distance field and use the Field Calculator with a python script to compute the distance..visual check the results using the Measure tool 35

36 I will post this presentation as a pdf at my website under the workshops section. Also in about a month I will have lecture notes and hands-on lab exercises posted on my nrm435 GIS analysis website that you can download. 36