This next field activity was looking in to how data points about an area can be collected more easily than using a co-ordinate system, as was used in the terrain model assignments. We learnt how to make use of some of the older and more recent technology that is available for surveying sights. Our aims were to firstly be introduced to and to try the equipment, then conduct our own group fieldwork. Then, the data needed to be used in ArcMap to produce a map of the data points collected. Throughout the process we were discovering the advantages and disadvantages of different technologies and techniques and some of the problems that people may encounter using these sorts of techniques.
The Study Area
The area we used to practice with the new equipment was located just outside of the academic Science building where our class is held, on the University campus. The area is fairly flat and contains a number of different features with green areas, woodland, car parking space, pavements, lampposts and various signs for the University. Figure 1 below, shows an areal image of the area.
Figure 1: Aerial image of the first site used to carry out fieldwork. (C. Google Earth)
Methods
In class we were introduced to three different types of equipment that can be used to gather information on the distance and azimuth of a point from a source. We then moved outside as a class in order to all have a go at trying each of the methods and to discuss what sort of things we should measure and what should be taken in to account when picking a study site.
One: A filed compass with a built in azimuth viewfinder. Figure 2 below, shows an example of such a device. This is a more basic method that involves less high-tech technology, but is a multistage device. By looking through the viewfinder towards the point you are measuring you can read the scale to collect data on the azimuth of the object from the point of origin.
Figure 2: An example of a field compass with a viewfinder for reading an azimuth recording.
Two: Handheld laser distance measures, this includes two devices, one is held at the starting point and another at the point you are collecting data about and when pointed at one another the distance is recorder digitally on the first device. An example of these devices is displayed in figure 3.
Figure 3: An example of handheld laser distance measures for use in fieldwork.
Three: Trupulse Laser Rangefinder, we found to be the best all round option for ease in the field. This device can be pointed at a recording point and a you can select using buttons on the side what you want to calculate, so both the distance and the azimuth, are displayed and can be read easily and quickly off the screen. An image of what can be seen through the viewfinder and an the device itself is in figure 4 below.
Figure 4: The Trupulse laser rangefinder and what can be seen when looking through it when it's in use.
My group decided that we were going to survey trees, and then decided on our location as discussed previously. A table was constructed before going out in to the field to make the data collection more organised and speedy. Said table with it's filled in value is shown in figure 5. We decided to bring a tripod out with us in order to guarantee, that the origin for the points would be exactly the same, figure 6 is an example of my group collecting and recording data. The attribute we decided to collect was the point type as we felt this would be the quickest and easiest to gather seeing, as we had to wait till late on in the week until everyone in our group could meet to do the fieldwork. Once we were actually at the site we also saw and decided that we would have to record more features than just trees in order to make up one hundred points. So, once having a look through the viewfinder to see where our maximum range ( 1-4 to 1 hectare plot), and then selected points to measure and the point number, attribute type, distance from origin (m) and azimuth from origin (Degrees) were collected.
Figure 5: The table that our group used post data collection in the field.
Figure 6: Two members of my group collecting data using the Trupulse and recording it into a spreadsheet.
This table was then converted into digital form by typing the values into a excel spreadsheet, A base map satellite image of the field area was added to a blank map in Arc GIS (figure 7), and then using the same corner that we measured from on the nursing building we were able to read of the bottom of the screen the origin x and y co-ordinates, by holding the cursor over it. The x and y co-ordinates were then added to each data poin in the table, in order to be able to export the table to Arc Map.
Figure 7: The base map used in ArcMap to display recorded points on.
A geodatabase was set up in Arc Map and then the excel table was imported in to it. ArcToolbox was opened, then we went in to Data Management, Features and double clicked Bearing Distance to Line. A window then opened up where we had to select or data table as the input and select the various fields, then the lines were added to the map to show the distance and azimuth from our starting point, as conveyed in figure 8.
Figure 8: The AcrMap basemap once the Bearing Distance to Line tool had been applied.
We wanted to have our data displayed as points also, to in the same features toolbox the Feature Vertices to Points command was used, and the same process as before was applied. Figure 9 now shows the final map created from our fieldwork.
Figure 9: Final Map of the distance azimuth survey on campus.
As mentioned slightly in the methods section, as a class we decided that the Trupulse laser rangefinder was the best for carrying out our fieldwork. As, it is able to carry out a greater number of measurements the other pieces of equipment, the data is displayed for you so you do not have to read it off a scale, and if you were by yourself you could carry out fieldwork alone fairly easily.
When we arrived at our site we were able to see just how much of our view was obstructed by the buildings and how many data points would be within our distance range, and it did not look like enough, so it meant we had ti branch out to different types of points. But I think it gives a better impression of what is actually at the location. Also, with the trees it was quite difficult to tell them apart at this time of year, as they were closely situated next to each other, had shed their leaves and were covered in snow.
Towards the end of our data collection there was some precipitation starting to fall which was obstructing the lens, so we had to make sure that was clear. Entering the data in to excel was fairly time consuming and can be quite frustrating when you already have it in a table from and it's just not digitised. So we have decided that during future field work, (weather permitting) we shall use my iPad to record the data on, so that it goes straight in to a digital form and can save some time.
The first few times that the Bearing Distance to Line feature was used it failed, as some of the table categories and names contained numbers and punctuation which did not allow the tool to run, so this had to be altered. Bright colours had to be used for the line and point displays in order to be visible against the satellite image.
This technique for collecting field data is very useful as it is much easier to be able to stay in the same location with all your equipment and record data than having to go out to each point, especially if you were doing this on a larger scale. It is time effective, and as previously mentioned is suitable if you were carrying out a project alone. It can be used for nay form of data collection where you need to measure how far away points are from each other, their distribution, the prevalence of something occurring. It can in many cases be used in conjunction with GIS or in fact replaced with GIS if no fieldwork were to be involved.
The gathering, recording and displaying of data seemed to all go well, and so I feel that our results are probably fairly accurate. Especially seeing as we made use of a tripod, it meant that we could ensure that all the measurements originated in exactly the same location. Of course there is always the chance that technology will fail you and perhaps won't be completely accurate, or that they may be read or recorded wrong.
Also, with Azimuth calculations there is always the problem of magnetic declination, this is the angle between North and true North. This varies according to location and changes over time. Using the National Oceanic and Atmosphere Administration website, you can calculate the magnetic variation for your site, the calculation for our groups fieldwork site is shown in figure 10.
Figure 10: The NOAA calculation of the magnetic declination for our azimuth survey fieldwork location.
Conclusions
There are many different methods and instruments that can be used nowadays to measure the distance and azimuth of selected features whilst carrying out fieldwork, one that can calculate a wide variety of measurements quickly and easily is preferable. it is important when collecting points from a source, that the source remains the same each time, and magnetic declination must be taken in to account when calculating the azimuth. Tables being used in ArcMap must have simple headings and titles in order for tools to run successfully. The type of data that you can collect whilst doing fieldwork can alter when you see the site for real than when you look at it on a map or are planning, and some things may be more difficult o see or measure depending on the weather conditions.
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