Topographic Survey Methods

Introduction:

This exercise provided an introduction to topographic surveying methods during two weeks, and were required to use two different surveying methods to complete the tasks. The goal in these two exercises was the same: to collect survey-grade GPS points outlining the microtopology of the mall area on the UW-Eau Claire Campus.

This image shows the area of the UWEC campus that we were to examine with our topological surveys.

The difference was in the methodology and technology used to complete this. The first week, students were provided with a TopCon HiPer GPS unit, and Tesla Handheld. The handheld unit connects to the HiPer GPS via bluetooth, and to a Verizon MiFi mobile internet hotspot to maintain internet connection throughout the survey.

Handheld and Internet Hotspot

TopCon Tesla Handheld GPS unit. This unit is also capable of collecting GPS points, but not with the accuracy that the HiPer provides, so we used it for control purposes through use of its Magnet Field software.  It was mounted on the tripods for easy access. This unit was used in both sampling methods.

This is the Verizon MiFi unit that provides a reliable wireless internet connection for surveying. This was also mounted on the tripods.

Dual Frequency GPS Unit

TopCon HiPer GPS Unit. This is mounted on a tripod with leveling gauge, which maintains data accuracy.

Total Station

TopCon GPT - 2500 Total Survey Station. This device operates differently than other GPS retrievers: it is stationary, and its laser is then directed at a reflector pole to collect points of interest. An occupied point must first be acquired. This is where the Total Station will stay throughout the survey. Next, a backsight point must be taken. Both of these can be acquired using a GPS. The backsight point must be shot from the total station to the reflector pole as well- this sets up the ground to grid relationship to ready the total station for data collection. 

Using these two very different methods, the same goals were reached in this exercise. It allows for a comparison of the methodology to determine the equipment best suited for a given job. 

Methods: 

The first week in the field included using the HiPer Dual Frequency GPS Unit to conduct our topo survey. It was very important to follow the instructor's detailed lesson on how to operate the software, and what steps to follow in preparing to go out into the field. This included properly connecting the Tesla handheld unit to the HiPer GPS, and connecting to the MiFi internet, along with properly creating, setting up, and opening a job for use in the Magnet software. Once this was done, we went out into the field. With the software properly set up, and the GPS and handheld mounted to a tripod, collecting points was relatively easy.

A picture of me operating the HiPer GPS / Tesla Handheld system. The tripod allows for leveling, which increases the accuracy of the point. When taking each point, we used point averaging for 5 points, which took around 7 seconds, based on the GPS' signal. This provided a more accurate point than the 3 point default setting. A total of 100 points were taken using this method, and were later imported into ArcGIS for analysis.

The next week, the Total Station method was to be used. It was equally, if not more important to follow our instructor's directions in this exercise, as this method requires even more equipment, software, and methodology. In fact, it took my partner and I one failed attempt to collect points before we were able to set everything up correctly and collect data.

First, it is necessary to collect an occupied point. As previously mentioned, this is the place where the total station will stay throughout the survey. The occupied point was collected using the HiPer GPS in the same way it was used to collect points the past week. When this was accomplished, it was necessary to collect a backsight point. The HiPer collected this point as well. These points were marked by flags, and stored in the Tesla handheld unit for use later in the survey. Next, we disconnected the Tesla unit from the HiPer GPS, reconnecting with the Total Station. This was not a smooth process, and as was discovered quickly, the HiPer had to be turned off, and the Total Station had to be restarted for the Tesla to connect to it properly.

Next, the Total station had to be set up directly above the occupied point. This involved setting up the tripod, placing the Total Station on it, and then using a laser finder device to ensure that it was directly above the flag that had been set previously. Also, It had to be leveled, using a number of leveling gauges on the device. This was difficult, but necessary to ensure proper accuracy: these high-grade survey systems are only as accurate as they are properly used.

In the Magnet Software, the backsight and occupied point had to be set up before points could be collected. This included selecting the previously collected points from a list, and then sending someone with the reflector pole to the backsight to be shot with the Total Station's laser. This also included inputting the height of the Total Station and the reflector pole. Once this was finished, properly defining the ground/grid relationship, data could be collected.

Groupmates shooting the Total Station laser at the reflector pole. Once this was properly aligned, another person would save the point on the Tesla device (See below)

Myself and a groupmate shooting the laser and recording points

Myself and a groupmate recording points and shooting the laser

A number of points were collected using this methodology. The increased group size this week allowed for each member to cycle through the different tasks associated with operating the Total Station.

The data was then exported from the Tesla device to a text file, and transferred to the PC. It was then edited slightly before being imported into ArcMap as (X,Y, Z) data. The resulting points and micro topologies are shown below in the results section. See the below tutorial video created by Martin Goettl for more information on exporting data from the Tesla device.

Results:

This image shows the results of a Kriging interpolation method on the collected data points after being imported into ArcMap. It includes the original points, as well as the interpolated surface. For more information on Interpolation Methods, see ArcHelp

Kriging Interpolation surface with overlayed points collected using the Total Station.

Discussion:

The results of the two maps are not extremely significant. It is certainly worth noting that the dataset collected with the HiPer GPS system did not provide an accurate representation of the topology of UW-Eau Claire's campus mall area. The points were not interspersed enough to provide the Kriging model with proper data. The resulting dataset for the Total Station is much more complete, and provides a decent model.

However, what is more important than the maps themselves is the different methodology used to collect them. There were two very different methods used during these two weeks, and I think that each method has its pro's and con's.

The HiPer Dual Frequency GPS system was relatively easy to use, and was operable by just one person. However, it was a hassle to move it from point to point, then level the tripod legs before collecting each point.

The Total Station method, once set up was faster to operate, as it just took someone moving the reflector pole, and another person shooting it to take a point. It was less clunky to move around, but was extremely difficult to set up. As mentioned before, my partner and I went out into the field once and never were able to collect data because the setup was done incorrectly. As is mentioned above, this method also requires at least two people for operation, which can be seen as a con.

Each system is capable of collecting very accurate data, so it is a matter of the application to determine which is better suited for a given job. Since the HiPer system is harder to move around quickly, it would be recommended to use the Total Station on jobs that require many data points. On the other hand, for smaller-scale studies, or for ones undertaken by only one person, the HiPer system would be ideal. 

Conclusion:

Using two different methods with different tools to accomplish topographic surveys allows for comparison of methodology. Being able to determine which geographic tools are best suited for a given job is important, as it can make field work much simpler. In this particular case, each system is able to yield very accurate data, so it is a matter of determining which is more practical in certain situations. This is an important skill to have as a geographer: being able to select the most effective tool from an array of them, and to plan around it accordingly. As other exercises in this blog demonstrate, it is also to not rely too heavily on any one method, as technology can and will fail. Because of this, it is important to understand the multiple methods that are available to accomplish a given goal.

Distance Azimuth Survey

Introduction:

This lab was an introduction to surveying using the distance azimuth technique, which is simple but usable in many situations. With today's technology, it is possible to acquire very precise location data, but it is important to recognize the fact that this technology can fail. Professor Hupy stressed this, saying that it WILL fail, whether it be from low battery life, adverse weather conditions or other failures. Because of this, it is vital to know the basic techniques in field methods to be able to function effectively, independently of advanced technology. This exercise included using a TruPulse laser distance finder to record distance and azimuth readings for a minimum of 100 data points of our choosing. 

TruPulse laser that was used to record distance and azimuth readings for our features. 

My partner Emily Moothart and I chose to survey cars in the Phillips parking lot of UW-Eau Claire.

This is an aerial image of our study area. Note that this photo is not current, but the parking lot that we were studying still is very similar to this. 

This image shows a panorama view of the parking lot we surveyed.

We were also advised to take note of the concept of declination before starting the survey. This basically refers to the difference between magnetic North and true North. This can cause error in taking azimuthal measurements based on location changes over time. Luckily, our particular location here in Eau Claire, WI has a small declination value, so it is negligible in this study. For more information on this concept, see the below video. 

The other concept that is important to consider is the difference between explicit and implicit data- in this case as it relates to grids or coordinate systems. An explicit system uses real coordinates to delineate features, where an implicit one uses arbitrary grids to do so. The result is that implicit grids only show relativity between features, without reference to its spatial location, where explicit grids do include that. This particular exercise is a kind of a cross between the two. We will calculate the locations of features without using any actual coordinates, but afterwards we will assign our starting point real GPS coordinates so that the whole thing will be usable in the GIS. 

Methods: 

Once we decided our area of study, we went to our starting point to begin surveying. We set up the TruPulse and Tripod and began taking readings of cars from left to right. The process was slow at first, but picked up relatively quickly as we became accustomed to the process. I personally operated the TruPulse as Emily recorded the readings as well as the type and color of each vehicle, on paper. 

An image of me firing the laser at nearby parked cars.
Photo by: Emily Moothart

Another image of data collection with TruPulse unit.
Photo by: Emily Moothart

It was a very warm day, but heavy winds made data collection difficult at times. The tripod would shake in the middle of firing the TruPulse, which would not allow it to get valid distance or azimuth readings. We switched halfway through so that each of us got experience in operating the laser and recording. Due to time constraints, we weren't able to collect as many points as would have been ideal. Another group of students needed to use the equipment, so we settled with just 92 features. 

After returning inside, we transferred our data into an Excel spreadsheet for later use in ArcMap. A preview of some of our points is shown below.

This shows the excel document containing points for each feature we surveyed. 

An important thing to note before proceeding into ArcMap for mapping the surveyed data is to take note of the point of origin. This means noting the exact GPS coordinates of where we were when we were firing the laser distance meter. Using one that is easily identifiable by satellite imagery is a good idea. To find ours, we added a placemark to Google Earth imagery to yield the coordinates of where we had just been conducting our survey outside. Once found, it was added into our Excel table in x and y fields. 

Next, the Excel file was imported into the geodatabase, and we used the Bearing Distance To Line tool to convert the its information into a line feature class. 

Bearing Distance To Line tool. The first field requires the table with the inputted distance/azimuth data. The X and Y fields are the GPS coordinates mentioned above of the starting point. Logically, the Distance Field asks for the distance reading, and the Bearing field requires the azimuth reading. The rest of the options should remain default so that the distance unit remains meters, the bearing unit remains degrees, and the Spatial Reference remains GCS_WGS_1984. This spatial reference operates well with the coordinates used for the starting point. 

This tool's output results in a number feature class of lines, heading to the angle recorded in Bearing and ending at the distance recorded in Distance. This is shown below in the results section. Once this tool creates the lines, the Feature Vertices to Points tool can be used to create a point feature class from their endpoints. 

This image shows the location of the Feature Vertices to Points tool. The tool is simple, but it is important that the "Point Type" field is set to ENDPOINT so that only the endpoints are created, rather than the endpoints and beginning points. 

The results of this tool are shown below. 

Results:

This is the final map showing the results of the distance/azimuth survey and its integration into ESRI ArcMap. Features are classified by type.

Discussion:

The outputs from the tools indicate that there is substantial data associated with our surveyed points. After searching through our dataset, I don't believe that there is any input error. This means that the error must have come from taking our readings. When looking at the image of our lines, it becomes obvious that even a little bit of error in calculating the azimuth will result in a large margin of error for the resulting point. An even more probable source of error comes from recording distance. If we didn't get a proper fix on the feature we were aiming at; say we missed and fired at a tree behind the car, this would become apparent on the above map. 

A strange pattern is shown in the final map where the points as they get farther away seem farther and farther south of their actual locations. Though it may be worth noting that the aerial image used as a basemap is not current, it really should not affect the distribution of our points because cars still park in the same places as they did when the image was taken. A more likely explanation is the fact that the laser's accuracy decreases as features get farther away. This comes from the TruPulse's decreasing accuracy with distance, but more significantly with the user's error as distance increases. It takes a couple of seconds to hold down the fire button on the device, while maintaining a fix on the desired feature. At high distance, this becomes difficult. Also, the adverse weather conditions should be noted as a potential source of error. If the tripod was moved by wind, all subsequent readings would be slightly off. 

Conclusion:

Though we did use an expensive laser distance finder device in this lab, it could have been conducted using much simpler tools. The purpose of conducting this survey was to familiarize ourselves with alternate methods for calculating spatial relationships among features using an implicit coordinate system. This type of survey is useful in situations where access to advanced global positioning may not be feasible either because of lack of resources, or because of technological failure.