In the following text, you can read a great thesis of a colleague Nebojša Vračar
Collecting and preparing of topographic maps
Raster data, ie the basic map was obtained by digitazing military topographic maps, made in te seventies of the last century. These maps served as the basis for making maps for use in forestry. Vector data such as the boundaries of compartments and sub-compartments, management units as well as primary forest traffic infrastructure networks were obtained from the IRPC, while vector data on secondary forest traffic infrastructure were obtained by methods and means thet will be presented and explained below. Before going to the field in order to record secondary forest traffic infrastructure, it is necessary to transfer the map to a GPS device or smartphone for easier orientation in forest space. Map transfer is done using QGIS, Global Mapper or MAPC2MAPC, depending on which type of device will be in use in the field. Typical output formats are .kmz used by Garmin devices, .rmp used by Magellan devices, or .otrk2 (.xml) used by smartphones, or OruxMaps applications. Figure 9 presents a topographic map of the former Glamoč military area, sub-area of Zableće in the scale of 1:25 000 and represents a part of the territory of FMA „Ribničko“, which was digitized, georeferenced and later adapted for use in forestry.
Maps transfering to smartphone in the OruxMaps application
Vector and raster data complexed and edited in QGIS can be exported and transferred to GPS devices or mobile phones. Switching the map to mobile phones for further use is done by exporting the project being worked on in QGIS in .tif format, then opening it using the MAPC2MAPC application and converting it for use using the OruxMaps application. The resulting converted file needs to be transferred to a directory on the phone oruxmaps/mapfiles and then uploaded to the application. ( more about that)
Recording coordinates in the field using GPS device
When going to the field, before starting the work on recording forest communications, it is necessary to start the GPS device in order to establish a connection with GPS satellites. After the connection was established, in this particular case, coordinates (points) were recorded at specific places: landings on the primary forest traffic infrastructure, at characteristic bends on skid trails, at road junctions and at the ends of the road. The points thus obtained will later be used to connect into routes and finally obtain a network of secondary forest traffic infrastructure. In addition to the above method, there is also a method of recording traces, in which the device is set to monitor the movement of the position of the device, where the device constantly records the coordinates while moving. The lack of this method is the overlap of the trail when constantly searching for a location and the need to constantly pause the trail during field research.
Connecting coordinates of secondary forest traffic infrastructure into routes
After the work in the field, the connection of coordinates (points) of secondary forest traffic infrastructure into routes. The whole process is very simple and in this case it was done in the Garmin BaseCamp program used for Garmin devices. In addition to this method, it is also possible to connect points directly on the device itself. After merging the coordinates into routes and marking objects such as warehouses, pits, springs, watercourses and other important objects, this data is exported in the form of a .gpx file that will serve as input vector data for processing in GIS, specifically in QGIS program.
Display and processing of the network of secondary forest traffic infrastructure on the map
The previously created file is imported into the QGIS program as a vector data source. After importing, you get one basic look that needs to be edited and adjusted for display on the map. In order to get the final look of the vector data, it is necessary to manipulate and edit the imported layers in the QGIS program. To perform these operations requires a higher level of knowledge of the program than average. After the vector data file is imported, it is edited. The program displays the specified files in the form of layers. Right-clicking on the desired layer opens a tab where you need to select the last item „Properties“. Clicking on the specified item will open a window with all the properties of the layer to be edited. In the newly opened window (Figure 11) there are a number of options, two of which are important for visualizing and editing the layer, namely „Symbology“ which selects the color and width of the layer (eg color and width of a skid trail, compartment boundaries, skid road etc.) and „Labels“ in which the manner, appearance and position of vector data names are selected.
Relative forest accessibilit
The relative forest accessibility tells us pictorially and numerically about the accessibility of the network of forest traffic infrastructure, ie about their spatial distribution. The relative secondary forest accessibility is calculated by the buffer creation method. Buffers are areas around a secondary forest traffic infrastructure that are characterized by equal distance of endpoints from the road. To calculate the relative secondary forest accessibility by the method of creating a buffer for the secondary forest traffic infrastructure network, the length of the rope on the winch used for approaching (40-60 meters) is taken into the buffer. The result of calculating the relative secondary forest accessibility is obtained in the form of an image and a numerical indicator. The ultimate goal is to achieve a secondary relative forest accessibility of 100%. As the length of the rope on the winch is measured in a straight line and the slope of the terrain is not taken into account, it is necessary to reduce it for the correction factor which is conditioned by the curvilinear extraction and slope of the terrain (Sokolović and Bajrić, 2013).
Accessible area (%) Category of forest accessibility
to 60 Insufficient accessible
60 – 70 Poorly accessible
70 – 80 Hardly well accessible
80 – 90 Very well accessible over
90 Excellent accessible
Next figures present the relative forest accessibility for different rope lengths according to Sokolović and Bajrić (2013), but also on a specific example during the research in Forest management (FM) „Ribnik“. In the above pictures, black lines represent skid roads; red color represents buffers, white surfaces that are not within range of the winch rope, while dashed lines represent the boundaries of the compartment.
Creating a buffer zones arround forest traffic infrastructure in QGIS
Buffer zones are areas around a forest traffic infrastructure that are characterized by equal distance of endpoints from them. Practically, the buffer zone of secondary forest traffic infrastructure represents the area that is within the range of the tractor rope, ie the area that should be the subject of remittance. Buffer zones are created by opening the Vector drop-down menu in the QGIS program, then Geoprocessing tools and then Buffer (Figure 14). In the new window (Figure 15), the necessary parameters are set, such as the width of the buffer zone, the appearance of the edge of the buffer zone (sharp, round, etc.). After completing the settings, clicking on the Run button gives the final appearance of the buffer zones, which can be further edited in the way explained in the chapter on visualization in QGIS.
RESULTS
The main goal of this research is to examine the possibilities offered by QGIS when presenting the network of secondary forest traffic infrastructure. There are many possibilities, and further in the text as research results will be presented those that are of the greatest importance in terms of improvement and acceleration of work performed during the marking of secondary forest traffic infrastructure, their display on maps, calculating the total length of secondary forest traffic infrastructure, coverage of forest area by skid trails or roads at different rope lengths, the ability to quickly and easily calculate the length and area on the map and some other improvements.
Making of technological map of timber harvesting and silviculture for plan of operations
After the completion of all field work, merging coordinates of each point on the secondary forest traffic infrastructure into routes, exporting files with vector and raster data, the preparation of a technological map of timber harvesting and silviculture for printing in the QGIS program, which will serve as a mandatory attachment to each plan of operations. The job of editing input and making maps requires little more than the skills possessed by average computer users. Imported vector data, ie lines representing skid trails or roads (Figure 17) need to be refined in order to be recognizable on the map. After selecting the colors and other parameters for the vector data (Figure 18), it is necessary to make the appropriate legend. The map can be displayed in any scale, and according to the Methodology for the preparation of the plan of operations of the FM „Ribnik“, scales of 1: 5,000 and 1:10,000 are recommended. Preparing the map for printing begins by clicking on the „Project“ function, then on „New Print Layout“. A new window opens in which the new map to be printed should be named. This can also be done by using the „Ctrl + P“ key. After naming, another window with map editing tools opens (Figure 19). Depending on the need, the map can be set to landscape or portrait. On the left side are the tools used to select an object to be added (map, legend), tools for adding a map, image, legend, another object and the like. After setting and editing all the above parameters, the map can be printed directly in color in the desired number of copies on A3 or A4 paper, depending on the size, or reported in digital form for presentation or storage on portable devices.
Practical application of buffer zones when performing marking tree work
As a rule, after reconnaissance of the terrain and completion of works on marking the network of secondary forest traffic infrastructure, marking of trees for felling follows. When performing marking tree work, it is necessary to take into account the range of the rope of the winch. According to Sokolović and Bajrić (2013), ropes with a maximum range of 60 meters are used in our forestry operation. In insufficiently accessible forest areas that are out of the range of the rope, it is necessary to plan new skid trails or roads if the field conditions allow it, or otherwise plan other technologies of timber harvesting such as animals and cable yarders. For this purpose, 60-meter-wide buffers can be created on the map, reduced by the slope coefficient, then the map can be exported to a file of the appropriate format and transferred to a mobile phone in the OruxMaps application. After reading the location and moving, you can clearly see on the mobile phone which space is within range of the rope and where the marking trees should be made.
The relative secondary forest accessibility of the compartment 47 at a rope length of 60 m is 89%. It was obtained on the basis of the accessible area, which for the mentioned rope length is 91.03 ha, and the total area of the compartment, which is 102.47 ha
Determination of the length of skid trails or roads
When using the old methods, the lengths of forest traffic infrastructure were obtained by measuring with a measure tape in the field, or with the help of a curvimeter and a ruler on a map. These methods require a lot of time and from the aspect of today’s business are not profitable. The total length of skid trails or roads is very easy to get using the attribute table in QGIS, by right-clicking on the layer representing the vector data, go to the Open Attribute table option, mark all parts of the layer, in this case the skid trails or roads with the corresponding arms. Then a new „length“ field is added in the „Field Calculator“ tool which will give the length value. By clicking on the OK button, the length of all skid trails or roads will be obtained, which can be very easily copied and more clearly displayed in one of the word processing programs.
Determination of area using by QGIS
When creating the project of operations, it happens in several cases that it is necessary to calculate an area in the compartment. Specific cases are, for example, when dividing compartments into gravity zones and working fields, where it is necessary to determine the assigned timber volume per hectare in order to determine working conditions and norms, or when marking groups, afforestation areas, crop cleaning areas, etc.
By creating a polygon within the boundaries of the gravity zone, the area of 9.90 hectares was obtained. This method is very fast, reliable and accurate. It is possible to set the output values to be in different units of measurement (hectare, ar, square kilometer, etc.). In addition to the above method, the determination of an area on the map can be obtained using the layer attribute table, similar to the determination of the length of skid trails or roads. There are two possibilities: importing vector data obtained by recording a surface directly in the field using a GPS device or mobile phone and then converting it from a line to a polygon, or creating a new polygon. As for the first option, the polygon is obtained by opening the Vector / Geometry tools / Lines to polygons option. A new window opens in which you need to select the Input layer. By clicking on the Run button, a polygon of the surface is obtained from the line. As for the second possibility, first you need to make a polygon for an area (compartment, sub-compartment, work area, group, etc.). The polygon is created by opening the Layer / Create / New ShapeFile Layer option. A new window opens in which you need to set the parameters for the new layer. After finishing setting the parameters, a polygon is made on the map. The area of the polygon is obtained using the attribute table by opening the attribute table for the desired layer and in the newly opened window the layer for which the area value is to be obtained is marked. A new virtual field „area“ should be added to the „Field Calculator“ tool. Clicking on Ok gives the surface value.
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