Low-tech Distance Azimuth Survey Practice

Introduction

Sometimes technology fails. For times when GPS and other technology has failed or cannot be used, low-tech options need to be understood for supplemental implementation. One of these low-tech options is distance azimuth surveying. In its most basic definition this is the collection of a single coordinate point, a distance, an azimuth (bearing), and data about the object being located.

We practiced this method on Putnam Drive, behind the Phillips science building and the Davies student center on the UW - Eau Claire campus. We measured distance of ten trees from each of three points, each point's GPS coordinates, the azimuth of the tree from the point, and each tree's circumference. Though GPS coordinates may not be available for collection of the initial point in situations requiring this type of survey, a landmark could be picked to measure distance and bearings from, and this could be pinpointed later in georeferenced or orthorectified aerial imagery to find the coordinates.

Methods:

Like stated before we went as a class to Putnam Drive to survey in three groups of about 6 each. Trading jobs periodically each member of each group did every job for practice. At one of the three points being surveyed from a compass (of the type that is looked through with one eye to see the azimuth while the other eye is fixated on the appropriate point) and a tape measure were used. At another area, a compass and a distance measurement device with two pieces (one with the measurement reading and one that the other unit used to get its measurement) were used. At a third point being surveyed from a laser gun was used that gave both distance and azimuth readings. At all points being surveyed from a small tape measure was used for measurement of the circumference of each tree. This was measured in centimeters, while the distance to the tree was measured in meters and the azimuth was measured in degrees.

After collecting this data in the field on paper the table was brought into Microsoft Excel. The table created for this project is shown in Figure 1. One important detail with the creation of this table is that capitals and spaces should not be used for the column titles. ESRI software will choke on processing the data later if these are used. Also note that the GPS coordinates observed from the three unique survey points are stored in the x and y fields.

Figure 1

After creation of this table the data could be brought into a new ArcMap map. The table contained within the excel file was brought into the table of contents. In ArcMap a new file geodatabase was created and named the default geodatabase for the map file. This can be seen in Figure 2.

Figure 2

The data was now converted into lines by using the Bearing Distance to Line tool. This was run with the parameters as seen below in Figure 3. All tools used in this project were found using the search function in ArcMap. This function can be seen alongside the tool in Figure 4.

Figure 3

Points were then created from the lines that were created in this last step by using the Feature Vertices to Points tool seen in Figure 4.

Figure 4

After creating these lines the final maps displaying the data were made which can be seen below under results in Figure 5. These were created in ArcMap by using a data frame for each map and adding the layers needed for each in each separate data frame (added by selecting the Insert menu, then Data Frame). Base maps were added by using the Add Data button  down arrow, then Add Basemap, finally selecting the topographic map in the resulting window. Text was added via the draw toolbar, and north arrows, scale bars, titles were added using the Insert menu.

Results:

The resulting maps created are shown below in Figure 5. Clearly seen in the top locator map are the three separate points surveys were conducted from. Below that map are the three separate areas surveyed in at a greater scale.

Figure 5

In reflection on the accuracy of the data, there are a few concerns. First is that after adding the basemap it was apparent that the initial GPS coordinates which marked the points from which the other points were taken (using distance and azimuth) were not accurate. These errors could either be attributed to poor GPS data or inaccurate basemaps, but it is far more likely that the error was caused by the GPS data accuracy. This is speculated because basemaps were created by ESRI, of whom the highest accuracy is expected, and because the data was collected at the base of a steep hill and under dense tree cover, where low GPS accuracy could be a possible issue. Also, the inaccuracy of the GPS coordinates made the points move to both sides of the road on which point one and two were collected from, and if the issue was bad digitization by ESRI the points would likely have only been on one side of Putnam Drive indicating a slight north-south inaccuracy in digitization. A different reason this GPS data could be wrong is that the coordinates were recorded by hand from the GPS unit, and the GPS unit may have simply not updated fast enough to the new location or a user could have written down a wrong digit. This GPS error would not be a problem however if a marked landmark or something else was used instead, possibly one seen from aerial imagery whose coordinates could be found later. In a situation in which you would not have a GPS unit, you would have no GPS coordinates!

Another concern is simple user error in reading the compass bearing. The compass with which one looks through and uses double vision to read is especially concerning. It is slightly difficult to get the correct reading. Instructions worth reading before attempting to use one of these compasses can be found here. This was not a problem however when using the laser distance measuring instrument which displayed a bearing at the same time as the distance to the object being pointed to with a click of a button.

Conclusion:

In a pinch, a distance azimuth survey works! In situations in which GPS technology is not available or cannot be used, and especially if practice has been had with the equipment that would be available,   moderately accurate data can be collected.

Pix4D Image Processing

Introduction:

Pix4D is software that can be used to create point clouds and orthomosaic images from UAS aerial imagery. The software uses advanced algorithms to take overlapping images from the data set and build a three dimensional model of the specific area observed.

Pix4D Basics:

What is the overlap needed for Pix4D to process imagery?

One necessity of UAS data for processing of UAS imagery in Pix4D is adequate image overlap. The recommended overlap in a general case is 75% frontal overlap and at least 60% side overlap. Pix4D also recommends that a regular grid pattern is used (as is shown in Figure 1) and that a constant height is used for data collection.

Figure 1

What if the user is flying over sand/snow, or uniform fields?

These conditions make it much more difficult for the software to find matching points in overlapping images for processing complex geometry and large uniform areas. For these conditions a minimum of 85% frontal overlap and 70% side overlap should be used. Also recommended is setting exposure settings accordingly on the sensor to get as much contrast as possible.

What is rapid check?

Rapid check is like regular initial processing but doesn't produce as good of an initial image.It is meant to be faster and just for ensuring that there is enough overlap for full processing later.

Can Pix4D process multiple flights? What does the pilot need to maintain if so?

It can however special care must be taken. The flight patterns of both flights must overlap sufficiently, the two flights must be taken in very similar visual conditions, and the spatial resolution (flight height) must be the same.

Figure 2

Can Pix4D process oblique images? What type of data do you need if so?

Pix4D can process oblique imagery for three dimensional models, but cannot create an orthomosaic in this mode. The software needs imagery at three different heights above the object being modeled, with each raise in elevation corresponding to a decrease in camera angle. This is shown in Figure 3.

Figure 3

Are GCPs necessary for Pix4D? When are they highly recommended?

Ground control points are not necessary just like georeferencing is not, but should be used in high precision georeferencing applications for the making of an orthomosaic. Situations where GCPs should be used are city reconstruction, and mixed nadir and oblique image aided reconstruction.

What is the quality report?

The quality report give you final quality information after processing of data. This report gives statistics and other information that aid the user in determining the quality and adequacy of the images created for their specific use.

Methods:

Figure 4

After opening Pix4D Mapper and clicking "New Project," a new project was made with a descriptive title including the name of the site, date, platform, and altitude, and was saved to my personal folder (Figure 4). Next, the images were added to the project (Figure 5). These came from the "Litchfield" folder including folders for two overlapping flights that was supplied by our professor. Now, due to an error not yet fixed in Pix4D the shutter of the camera model used and detected by Pix4D is set to global shutter when in fact it is a rolling shutter. This needed to be changed in the "Edit Camera Model" window so that the settings looked as shown in Figure 6. Clicking on, output coordinate system settings were not changed, and the "3D Maps" "Processing Options Template" was chosen. Now, processing steps 2 and 3 were deselected as shown in Figure 7. The "Processing Options" button also seen in Figure 7 was then clicked and under the third processing step tab the Triangulation method option was selected before the initial processing was started.

Figure 5

Figure 6

Figure 7

Now, after initial processing was completed and its resulting quality report examined (Figures 8-15), processing steps two and three were selected, "Initial Processing" was deselected, and final processing was run (Figure 16). In the quality report, good overlap was seen everywhere but the edges, where there was understandably less overlap. All images were used by the software.

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

After processing steps two and three finished, experimentation with the resulting DSM display options could be done. Turning off and on individually the tie points, point cloud, and triangle mesh, the various views were examined. A view of the triangle mesh is seen below in Figure 17. 

Figure 17

Another way to display the the resulting DSM was a flythrough video animation. By using the button highlighted in Figure 18, clicking the user recorded views button shown in Figure 19, recording individual points, and then using the parameters shown in Figures 20-21, I rendered a video. The video is shown under these.

Figure 18

Figure 19

Figure 20

Figure 21

Results:

After creating the video (shown below) maps could be created. These are shown in Figures 22-23.

Figure 22 (vertical unit is meters)

Figure 23

These two maps show the data in different ways and can be cross referenced for clarification about certain areas of the map.

In discussion of the data mapped, a few faults were found, however they are far from serious enough for the resulting three dimensional images to not be used for representation of the mine. First of all, the data is not of high enough quality to successfully recreate cars, tractors, and other machinery that was at the site. This can be attributed to the orientation and distance from these objects that the images were taken from. If recreation of these complex geometrical objects was the goal, oblique imagery from multiple angles and heights for the objects would have to be taken, and even then errors may occur. An example (a tractor) is shown below in Figure 24.

Figure 24

Another point of discussion of this data is that there were no ground control points taken or used, and thus the resulting image from the process is not an orthomosaic and simply a georeferenced image. To dramatically increase data quality, GCPs should be used.

One final point of discussion is that in the maps produced there was data that software tried to interpolate in the south portion and the north-west portion of the image mosaic that shouldn't have been processed. This could potentially be cut out by the clip tool in ArcGIS Pro or ArcMap.

Conclusion:

In conclusion Pix4D is extremely powerful yet fairly simple to use software given adequate knowledge and understanding of the data being used. For example, understanding of the sensor's technical qualities need to be known for fine tuning and a properly executed and planned flight with proper overlap both on the sides and the front are required. In the end data is produced that can be used both by the Pix4D software itself, and other applications such as ESRI ArcGIS applications or CAD applications. This data can be used to create maps of the color ramp symbolized DSMs, ArcScene scenes, or even processed to make hillshade rasters or other images.

Navigation Mapmaking

Introduction:

In preparation of actual navigation at the Priory, navigation maps were created. This post walks through the making of these maps, one in decimal degrees, and one in UTM meters displayed in a certain way for easy use in navigation. This assignment helped build map making skills, and understanding of coordinate system grids and other elements of maps that can help navigation. Special care was taken at every turn to create a map that was easily interpreted on the ground.

The Priory lands are owned by the University of Wisconsin - Eau Claire and include converted housing and hilly woods. Figure 1 below shows the area in the larger context of Eau Claire. It is located about 10 minutes south of campus.

Figure 1

Methods and Discussion:

To begin, data that was supplied by the instructor (via a file geodatabase) and copied to a personal directory was brought into a new ArcMap document. This new ArcMap document was stored in this copied geodatabase. Sorting through the data information that was deemed necessary for the map was kept in the document and layers of data that was deemed unnecessary was removed from the map. The layers deemed necessary were the boundary layer, the "grdn45w092_13" raster which contained elevation data for the area and surrounding areas, and an aerial image.

The first step in mapping was to choose an appropriate projected coordinate system. For this the NAD 1983 UTM Zone 15N Transverse Mercator was chosen. This coordinate system uses meters, a key difference from some other projected coordinate systems because everywhere else in this project meters were used as well. One particularly important place where meters were used was in pace counting, in which we counted our personal amount of paces per 100 m. This pace count step was added in for low-tech navigation distance calculation in the field. This initial step dictated this spatial unit being used in the rest of the project. This projection displays the given area well with minimal distortion as it falls in the UTM vertical strip type Zone 15N.

Going forward, from the raster elevation data provided a 2 m contour line layer was created. 2 m was chosen for the interval parameter of the contour creation after careful comparison to 1 m and also 4 m were also chosen and decided against for sake of the contour lines being too far apart or too close together. The 2 m interval made sure that the lines were far enough to be differentiated, yet close enough to give appropriate detail. For this the Contour (Spatial Analyst) tool was used after turning on the spatial analyst extension under Customize, then Extensions.

After making this 2 m contour line layer, it needed to be clipped by the boundary of the priory area. For this the Clip (Analysis) tool was used, and careful attention to the help section popping up on the right side of the tool window to make sure the right layers were used in the right parameter input areas.

The project culminated in tweaking the display and symbology of all of these layers, as well as of the data frame, and inserting other layout view objects to make the map appropriate for use in the field. The layers were displayed in the following order (from bottom to top): base aerial image raster, contour lines, and finally on top of those the Priory boundary. The display settings of the base image were changed so that the image was 20% transparent. This ensured that the other features on top of it would be fully visible, yet vegetation detail that would give important context for location in the field would still be visible. Next, the contour lines were changed to yellow which made them visible on top of the darker background image. After going into the layout view and making sure the extent of the ground needed for navigation was visible in the frame, it was time to make a grid. This was created by going into the data frame properties, clicking grids, then creating two new grids (one for the meters, and one for decimal degrees). The meter grid was created as a "Measured Grid", and the decimal degree grid was created as a "Reference Grid" in the creation process. The settings selected for these two different grids are shown below in Figures 2-3. The resulting grids were added one at a time to the map using the check boxes next to the grids, then used to create each map before each was exported as a PDF file.

Figure 2

Figure 3

The next step was inserting all of the other miscellaneous items that made the map functional in the field. A north arrow was inserted. A scale bar was inserted and changed to meters to keep the units consistent across the map. A scale text was also inserted. Other proper information added were the contour interval, a title, a watermark with name, a personal pace count, projection information, data credited to the instructor, and a legend that showed that the black boundary line was the boundary of the Priory land.

Results:

The process, careful to consider as many needs of the navigator on the ground as possible, resulted in the following maps (Figures 4-5)

Figure 4

Figure 5

Sources:

All data provided by Dr. Joseph Hupy

Survey123

Introduction:

Survey123 is a powerful platform designed by ESRI from which one can create and share surveys to be completed on mobile and desktop web platforms, analyze collected data, and download data atatched to spatial information for mapping and presentation. This post goes over how to specifically use the software to do those things, using an arcgis.com tutorial to go about showing all of the substantial features (https://learn.arcgis.com/en/projects/get-started-with-survey123/lessons/create-a-survey.htm).

Methods:

To begin a survey, log into an ESRI account on survey123.arcgis.com. From here, click create a new survey, then web designer. On the resulting screen options for questions can be viewed on the right-hand side of the screen. You can choose options that will give you questions with a small or large box for typing, multiple choice, single choice, time, date, geopoint, email, and more. For the survey created we used many different kinds of questions. To customize the question and its options simply click on the question and fill in the parameters on the right side of the screen. One key feature to use is dependent questions. These questions only pop up when a certain selection has been made on a previous question. The example that is provided below (Figure 1) is when "Single family (house)" is selected from a single answer question, the question "How many levels does your home have?" pops up beneath it. These are created by clicking the "Set Rule" button in the bottom right of a questions after it is selected.

Figure 1

After all question and parameters are set the survey can be published. After publishing however, the survey cannot be edited again (Figure 2). Now the survey can be shared and taken. A link can be shared by clicking on the share button (circled in Figure 3), copying the URL, then spreading the link to those who you'd like to take it, or it can be opened to completion by everyone by editing settings in the collaborate tab.

Figure 2

Figure 3

Finally, after data is collected (via url or Survey123 app), data can be analyzed and mapped. The data can be viewed in a multitude of figures in the analysis tab of the specific survey's page (tab seen in top bar in Figure 3). To map this data, ArcGIS Map Viewer can be used to make a map (link seen in bottom left corner of Figure 3). From here a map can be created zoomed in on the data points. Clicking on the "surveypoint" layer, then more options, then zoom to, we are zoomed into the neighborhood where the mock neighborhood association surveys were taken. Clicking on the same more options button, the rename button can be clicked to give the information a more descriptive name. Next, under the more options button, the pop-ups button can be clicked in order to configure pop ups for the user of the map to view. The parameter, "A custom attribute display," can then be chosen and a custom list of attribute configured to give the user of the map only pertinent information. This map can then be saved, giving the map a title and other attributes of information. Lastly, a web app can be made by clicking "share", then "Create a web map".

Results:

The map created from the survey can be viewed at arcg.is/1Lqm8j, and a screenshot is shown below in Figure 4. This map shows the data points collected in the Eau Claire student housing area. Clicking on these points, data collected for the location can be viewed. 

Figure 4

Conclusion:

ESRI Survey123 is a great tool to use if information needs to be collected from a known group or groups of people. The real power of the tool come with the mobile app which was created for it, from which one can download the needed survey, then can stay in a stationary place collecting data from passers by, or go door to door having people take the survey. This would be great for recruitment, homeowners association (like in this specific tutorial/example, or other organizations collecting data, especially when one needs to collect and display spatial information with a web map or other type of map.

Sources:

https://learn.arcgis.com/en/projects/get-started-with-survey123/