TOPOG: Workshops, Online Tutorial, Exercise 2

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TUTORIAL
Exercise 1 | Exercise 2 | Exercise 3 | Exercise 4 | Exercise 5

Online Tutorial
Exercise 2, Terrain Analysis

In this session, we introduce you to the following programs:

_mkbdy - prepare catchment boundary vertices information
_element - compute an element network
_sumatr - output some simple statistics on the element network
_param - compute some simple topographic indices
_underlay - define a subset region within a catchment
_xhistog - a graphical interface used to generate statistics on various topog files
_stripgen - generate a simple element network (planar, convergent or divergent)
Element networks will de prepared for the following catchments:

bullshead- steep, 84 ha catchment in the Brindabella Ranges near Canberra.
yahoo - gently undulating, 265 ha catchment near Mudgee, NSW.
planar - a simple planar hillslope generated using _stripgen.
con - a simple convergent hillslope generated using _stripgen.
div - a simple divergent hillslope generated using _stripgen.

2.1 The first step in performing a terrain analysis is to build up the catchment boundary information. We will begin by digitising some data on the screen.
Perform the following tasks:

run _display, using basename bullshead.
plot the DEM Contours (.tcn file).
plot the file bullshead.pts1; this has been prepared to show you the location of the five boundary vertices for this catchment.
for clarity, change the symbol style for this data file to medium-sized blue dots.
press the Digitise button; the control panel should read:

Polygon File bullshead.dat.a Poly# 1

digitise the five boundary vertices in an anti-clockwise direction, starting and ending on contour number 1 (z=1155 m).
press the New Poly button once: note that this changes to Save.
press the Save button once to save this file; the data points have been written to file bullshead.dat.a.
plot the file bullshead.pts2; this has been prepared to show you the location of the three valley axis heads for this catchment.
for clarity, change the symbol style for this data file to medium-sized red dots.
press the Digitise button; the control panel should read:

Polygon File bullshead.dat.b Poly# 1

digitise the three valley axis heads in any order you like; don't be concerned about the mess of lines you create.
save the results; the data points should have been written to file bullshead.dat.b.
quit _display.

2.2 We now turn to program _mkbdy; this automatically builds .hpt, .sad, .stl and .vrt files, using the data we have just digitised on the screen.
Perform the following tasks:

run _mkbdy, using basename bullshead.
enter filenames bullshead.dat.a and bullshead.dat.b as the two input files.
note that four files have been created.
using the editor, sequentially open the .hpt, .sad, .stl and .vrt files to study their contents.

2.2	We now turn to program _mkbdy; this automatically builds .hpt, .sad, .stl and .vrt files, using the data we have just digitised on the screen. Perform the following tasks: run _mkbdy, using basename bullshead. enter filenames bullshead.dat.a and bullshead.dat.b as the two input files. note that four files have been created. using the editor, sequentially open the .hpt, .sad, .stl and .vrt files to study their contents.

2.3 All of the basic information to perform a terrain analysis has now been compiled. We can now return to _demgen and compute an element network.
Perform the following tasks:

run _demgen, using basename bullshead.
select the _element option under the Run button.
use a value of 5 for the average trajectory spacing.
specify a terrestrial latitude value of -36.0.
quit _demgen.

2.3	All of the basic information to perform a terrain analysis has now been compiled. We can now return to _demgen and compute an element network. Perform the following tasks: run _demgen, using basename bullshead. select the _element option under the Run button. use a value of 5 for the average trajectory spacing. specify a terrestrial latitude value of -36.0. quit _demgen.

2.4 List the contents of your directory. You will note several new bullshead files:

File extensions What is it?

.atr element attributes

.cct element connections

.scct stream element connections

.elm element outlines

.sbd catchment boundary

.scn catchment contours

.stj flow trajectories

.stline valley axis lines

.rdline ridge lines

Perform the following tasks:

using the editor, study the contents of each of these new files.
run _display, using basename bullshead.
plot the DEM contours (.tcn) file.
plot the high points (.hpt) and saddle (.sad) files.
plot the catchment boundary (.sbd) file.
plot the calculated stream (.stline) and ridge (.rdline) files.
plot the trajectories (.stj) file.
press the Search button and select Element Search from the scroll menu.
click on a few elements to detect their addresses and centroid coordinates.
clear the DEM contours and plot the TOPOG contours (.scn) file.
sequentially map the Aspect, Equinox radiation and Slope values for each element (under the Attributes button).
after mapping Slope, select the custom.ctb colour/class table under the Legend button; note how this produces a clearer map.
plot the element network (.elm) file.
change the colour of the .elm file to black.
quit _display.

2.5 Run _sumatr using basename bullshead; note the minimum, maximum and average slope values. Such information is useful when you are about to build a customised .ctb file.

2.5	Run _sumatr using basename bullshead; note the minimum, maximum and average slope values. Such information is useful when you are about to build a customised .ctb file.

2.6 Let's learn how to modify a colour table (.ctb) file.
Perform the following tasks:

using the editor, open file custom.ctb and study it's contents.
copy this file to slope.ctb.
open slope.ctb and change the values.
run _display, using basename bullshead.
plot the slope map; the default colour table for a slope map is used in this instance.
apply the custom.ctb file, followed by the slope.ctb file; note the changes in the display.
quit _display.
edit slope.ctb again; this time change the colours to a suitable grey scale, using Appendix B in Topog Online as a guide.
run _display again to evaluate the effect of the change.

2.6	Let's learn how to modify a colour table (.ctb) file. Perform the following tasks: using the editor, open file custom.ctb and study it's contents. copy this file to slope.ctb. open slope.ctb and change the values. run _display, using basename bullshead. plot the slope map; the default colour table for a slope map is used in this instance. apply the custom.ctb file, followed by the slope.ctb file; note the changes in the display. quit _display. edit slope.ctb again; this time change the colours to a suitable grey scale, using Appendix B in Topog Online as a guide. run _display again to evaluate the effect of the change.

2.7 Now let's build a grey scale colour table the easy way. Using this strategy it is also possible to make a long, continuous grey scale table. We can do this by running program _ctb.
Perform the following tasks:

run program _ctb, using basename grey.
specify 40 for the number of grayscales.
specify minimum and maximum z values of 0.1 and 0.8, respectively.
run _display, using basename bullshead.
plot slope, using grey.ctb as the legend.
for context, also plot the .sbd, .stline and .rdline files.
quit _display.

2.7	Now let's build a grey scale colour table the easy way. Using this strategy it is also possible to make a long, continuous grey scale table. We can do this by running program _ctb. Perform the following tasks: run program _ctb, using basename grey. specify 40 for the number of grayscales. specify minimum and maximum z values of 0.1 and 0.8, respectively. run _display, using basename bullshead. plot slope, using grey.ctb as the legend. for context, also plot the .sbd, .stline and .rdline files. quit _display.

2.8 It's time to review our terrain analysis skills. Let's perform a terrain analysis for the yahoo catchment.
Perform the following tasks:

run _display, using basename yahoo.
digitise the boundary vertices information.
digitise the valley axis heads information.
build the .hpt, .sad, .stl and .vrt files using _mkbdy.
run _element, using a trajectory spacing value of 5 and latitude value of -33.
plot the various results using _display.

2.8	It's time to review our terrain analysis skills. Let's perform a terrain analysis for the yahoo catchment. Perform the following tasks: run _display, using basename yahoo. digitise the boundary vertices information. digitise the valley axis heads information. build the .hpt, .sad, .stl and .vrt files using _mkbdy. run _element, using a trajectory spacing value of 5 and latitude value of -33. plot the various results using _display.

2.9 Let's familiarise ourselves with program _param; this is used to calculate various topographic indices.
Perform the following tasks:

run _param, using basename yahoo.
select All parameters (option 9); this writes calculated values for all of the analy options to a file called yahoo.param.
run _display.
under the Simulation button, load file yahoo.param, noting that this is a multi-column file from which you can select a number of entries.
sequentially plot all of the entries in this file.
build customised .ctb files to suit Specific catchment, Convergence Index and Hillslope Length.

2.9	Let's familiarise ourselves with program _param; this is used to calculate various topographic indices. Perform the following tasks: run _param, using basename yahoo. select All parameters (option 9); this writes calculated values for all of the analy options to a file called yahoo.param. run _display. under the Simulation button, load file yahoo.param, noting that this is a multi-column file from which you can select a number of entries. sequentially plot all of the entries in this file. build customised .ctb files to suit Specific catchment, Convergence Index and Hillslope Length.

2.10 Now we turn to the histogram and statistics generator, _xhistog.
Perform the following tasks:

run _xhistog, using basename yahoo.
press the Files button and load files yahoo.atr and yahoo.param.
resize the control panel window to full length; minimise the size of the file list area.
highlight file yahoo.atr in the file list area.
press the Select button and choose Element slope, selecting the Frequency option; this plots the frequency distribution of slope values in pane 1.
under the Select button, toggle between Number, Frequency, Cumulative and Polygon; note the changes which occur.
return to Frequency mode.
note also the list of statistics which has been written to the top of the control panel window.
press the Options button.
under Options, select area weighting and output results to file slope.out.
in another window, view contents of file slope.out.
in pane 2, plot the frequency distribution of area values (from file yahoo.atr); use class file area.class.
deselect area weighting and output tabulated results to file area.out.
in pane 3, plot the cumulative frequency distribution of specific catchment values (from file yahoo.param).
use class file spec.class; output tabulated results to file spec.out.
in pane 4, plot the frequency distribution of convergence index values (from file yahoo.param).
use area weighting and class file conv.class; output tabulated results to file conv.out.
quit _xhistog.
using the editor, sequentially open files slope.out, area.out, spec.out and conv.out.

2.10	Now we turn to the histogram and statistics generator, _xhistog. Perform the following tasks: run _xhistog, using basename yahoo. press the Files button and load files yahoo.atr and yahoo.param. resize the control panel window to full length; minimise the size of the file list area. highlight file yahoo.atr in the file list area. press the Select button and choose Element slope, selecting the Frequency option; this plots the frequency distribution of slope values in pane 1. under the Select button, toggle between Number, Frequency, Cumulative and Polygon; note the changes which occur. return to Frequency mode. note also the list of statistics which has been written to the top of the control panel window. press the Options button. under Options, select area weighting and output results to file slope.out. in another window, view contents of file slope.out. in pane 2, plot the frequency distribution of area values (from file yahoo.atr); use class file area.class. deselect area weighting and output tabulated results to file area.out. in pane 3, plot the cumulative frequency distribution of specific catchment values (from file yahoo.param). use class file spec.class; output tabulated results to file spec.out. in pane 4, plot the frequency distribution of convergence index values (from file yahoo.param). use area weighting and class file conv.class; output tabulated results to file conv.out. quit _xhistog. using the editor, sequentially open files slope.out, area.out, spec.out and conv.out.

2.11 Let's get more familiar with some of the functions of _xhistog.
Perform the following tasks:

run _xhistog; load file bullshead.atr.
plot winter radiation in pane 1 and summer radiation in pane 2.
set both to read frequency and area weighted.
display the legends, using the Legend button.
move the legend around the screen using the mouse.
change number of panes from 2x2 to 1x2, using the Arrange button.
change each plot to a different colour using the Colours button.
press the Axes button.
add x major & minor grid lines to pane 1 for reference.
change x-max value in pane 2 to 0.5.
annotate each pane with a sentence or two using the Annotate button; click on the screen to drop the annotation onto the plot, then move it around with the mouse.
quit _xhistog.

2.11	Let's get more familiar with some of the functions of _xhistog. Perform the following tasks: run _xhistog; load file bullshead.atr. plot winter radiation in pane 1 and summer radiation in pane 2. set both to read frequency and area weighted. display the legends, using the Legend button. move the legend around the screen using the mouse. change number of panes from 2x2 to 1x2, using the Arrange button. change each plot to a different colour using the Colours button. press the Axes button. add x major & minor grid lines to pane 1 for reference. change x-max value in pane 2 to 0.5. annotate each pane with a sentence or two using the Annotate button; click on the screen to drop the annotation onto the plot, then move it around with the mouse. quit _xhistog.

2.12 This exercise explains how to define a sub-set area of a catchment, using program _underlay.
Perform the following tasks:

run _display using basename bullshead.
plot the Catchment Boundary and digitise a single polygon covering about 30% of the catchment; the saved file should be written to bullshead.dat.c.
run _underlay using basename bullshead.
specify polygon file bullshead.dat.c and output file bullshead.subset.
using the editor, view the contents of bullshead.subset; this records the address of each catchment element lying within the polygon bullshead.dat.c.

2.12	This exercise explains how to define a sub-set area of a catchment, using program _underlay. Perform the following tasks: run _display using basename bullshead. plot the Catchment Boundary and digitise a single polygon covering about 30% of the catchment; the saved file should be written to bullshead.dat.c. run _underlay using basename bullshead. specify polygon file bullshead.dat.c and output file bullshead.subset. using the editor, view the contents of bullshead.subset; this records the address of each catchment element lying within the polygon bullshead.dat.c.

2.13 Now, let's compare the frequency distributions of slope values for the whole and sub-set of the bullshead catchment, using _xhistog.
Perform the following tasks:

run _xhistog.
select 1x2 panes using the Arrange button.
in pane 1, plot the frequency distribution of slope values for the whole catchment using file bullshead.atr.
repeat for pane 2, but specify bullshead.subset as an underlay file using the Options button.
do the distribution of values differ?
quit _xhistog.

2.13	Now, let's compare the frequency distributions of slope values for the whole and sub-set of the bullshead catchment, using _xhistog. Perform the following tasks: run _xhistog. select 1x2 panes using the Arrange button. in pane 1, plot the frequency distribution of slope values for the whole catchment using file bullshead.atr. repeat for pane 2, but specify bullshead.subset as an underlay file using the Options button. do the distribution of values differ? quit _xhistog.

2.14 Create a simple rectangular element network by running _stripgen.
Perform the following tasks:

run _stripgen, using basename planar.
select option (0).
ignore the prompt for the transect name.
select option < 0 >, regular mesh.
specify 5 elements per contour, 10 contours, mesh width of 50 (metres) and mesh length of 100 (metres).
allocate slopes of 0.05 to 25 elements, 0.2 to 10 elements and 0.5 to the remaining 15 elements.
specify an aspect of 180 degrees, latitude of -40 degrees and lowest contour elevation of 100 m.

2.14	Create a simple rectangular element network by running _stripgen. Perform the following tasks: run _stripgen, using basename planar. select option (0). ignore the prompt for the transect name. select option < 0 >, regular mesh. specify 5 elements per contour, 10 contours, mesh width of 50 (metres) and mesh length of 100 (metres). allocate slopes of 0.05 to 25 elements, 0.2 to 10 elements and 0.5 to the remaining 15 elements. specify an aspect of 180 degrees, latitude of -40 degrees and lowest contour elevation of 100 m.

2.15 Now let's get _stripgen to build simple convergent and divergent element networks.
Perform the following tasks:

run _stripgen, using basename con.
select option (0).
ignore the prompt for the transect name.
select option < 1 >, converging mesh.
specify 20 contours and an outlet radius of 100 m.
specify a delta radius value of 10 m and an angle of 30 degrees.
allocate slopes of 0.05 to 10 elements, and 0.2 to the remaining 10 elements.
specify an aspect o 160 degrees and a base elevation of 300m.
now, run _stripgen again, this time using basename div.
select option (0).
ignore the prompt for the transect name.
select option < 2 >, diverging mesh.
specify all of the same input values as used above for con.
examine both element networks using _display; in each case, plot the slope values.
overlay the element network, and use the Search button to detect the upper and lower elements.

2.15	Now let's get _stripgen to build simple convergent and divergent element networks. Perform the following tasks: run _stripgen, using basename con. select option (0). ignore the prompt for the transect name. select option < 1 >, converging mesh. specify 20 contours and an outlet radius of 100 m. specify a delta radius value of 10 m and an angle of 30 degrees. allocate slopes of 0.05 to 10 elements, and 0.2 to the remaining 10 elements. specify an aspect o 160 degrees and a base elevation of 300m. now, run _stripgen again, this time using basename div. select option (0). ignore the prompt for the transect name. select option < 2 >, diverging mesh. specify all of the same input values as used above for con. examine both element networks using _display; in each case, plot the slope values. overlay the element network, and use the Search button to detect the upper and lower elements.

TUTORIAL
Exercise 1 | Exercise 2 | Exercise 3 | Exercise 4 | Exercise 5

last modified on 16 August 1997