Either way, I'm here to help demystify the mapping process for those who are confused and educate those who are interested. In this article I will break down the exact steps we take to produce high quality landscape base maps in a step-by-step easy to understand way. I hope you enjoy reading, and I hope you can walk away from this article with a little more understanding of what a base map is, how it's made, and how it is used in the design industry.
First, allow me to introduce you to "Theo." Theo is a robotic entity in the the genus of "digital theodolite," and species of "total station." This charming three-legged robot is responsible for collecting most of the information we use to produce a highly accurate digital map and is my #1 companion out there in the field.
What is a total station?
"A total station (TS) or total station theodolite (TST) is an electronic/optical instrument used for surveying and building construction. The total station is an electronic theodolite (transit) integrated with an electronic distance measurement (EDM) to read slope distances from the instrument to a particular point, and an on-board computer to collect data and perform advanced coordinate based calculations.
Robotic total stations allow the operator to control the instrument from a distance via remote control. This eliminates the need for an assistant staff member as the operator holds the retroreflector and controls the total station from the observed point."
Scene from movie "Castaway"
Theo and Me...
Disclaimer: Only read this paragraph if you are curious about"special" relationship" I have with Theo. Otherwise you can skip ahead to "The Process of Mapping a Property" section below.
For those of you that wish to know, Theo, who is often my sole "co-worker" out there in the field, has made an endearing impression similar to the iconic friend of Tom Hanks' character in the movie Castaway that he names "Wilson" and who also happens to be a volleyball.
While I have much love and admiration for the amazing abilities of this machine, I will admit that we have had our relationship ups and downs. Without going into to much detail, let's just say that although Theo is excellent at measuring precise relative distances and angles, she is not to big on conversation. I mean...I get it, we have a job to do, and she is a robot. Still, one tries to make a little small talk here and there just always gets back those blank stairs with that cold almost machine-like look in her eye. just looking at me...staring... peering into my very soul!
So, I think, "oh well, she is just a machine after all," I shrug it off and get back to work. At that very moment of course is when she decides it's actually not a good day to work anymore, suddenly flashes her little orange lights at me, and shut's off.
Or, my favorite is when she decides she wants to be a person instead of a robot with her own free will, stops listening to me, and starts looking away into the distance, daydreaming, and thinking about who knows what robots think about?
I just don't know....
In a nutshell it's an interesting journey getting to know this digital creature of metal, plastic, lasers, and microchips. Unless I learn to speak in binary code, however, I may never know what she is truly thinking. Don't worry about us, we always seem to work things out, and manage to succeed in producing many amazing maps together. Although I don't much talk to her anymore, I still hope that one day she will come around and we can be both co-workers and friends.
Stay tuned for more #adventureswiththeo
The Mapping Process
First of all, it is very important to set up the machine to be exactly level. Luckily we have a very nice digital theodolite that gets sent in for maintenance regularly and has a built-in leveling function. Once it is set up, calibrated, level, and lined up directly over the point we set in the ground, we begin by what is called "backsighting." This is what gives the machine a reference point in space to compare all of our other measurements.
In the yard we would place a nail into the ground (represented by the lower red dot) to mark an exact point on the property, and then place a second nail in the field to the side (the upper red dot) to mark another exact point. The yellow line going in between the two points now becomes the arbitrary reference angle (or "azimuth") that all other measurements will refer to.
For example we would walk over to the corner of the house above, the machine would track our prism, and we would command the machine from our wireless controller to shoot a laser beam. The machine will then reflect the laser off of the prism, measuring an exact distance and recording it's angle of rotation from the backsight point we had previously shot. The recorded point then goes into the handheld computer device, and the mapping process begins point by point by point until we have something that looks like the screen shot captured in the picture below.
Collecting Coordinate Points
Each point that is measured is given an exact coordinate in a 3 dimensional xyx digital interface based on it's relative distance and angle from the machine. This can also be described as North/South, East/West, and Elevation. We can use the computer to connect each point with lines as we go along building walls, pathways, roads and other elements into the map.
The screen shot to the right shows what it looks like when you start to accumulate multiple points. Each "X" marks a point on the map from a birds eye or "plan view", and you can see how the map is made using these coordinate points. Each line is made by connecting the various points as you go.
As we continue collecting points, we map everything we were contracted to include, which is usually our standard list of inclusions that can be viewed on our website
Elevations and Topography
At this point, you might be wondering how we measure elevation and calculate topographic contours. In this section I will describe in simple terms how this is done.
There are a few techniques we could use for this process. One way, as shown in this picture to the right is to use county LiDAR, from a free online source and overlay that onto our map. Usually, however, we use our total station to generate contours as described below
Each ground shot is used to create a grid, or web that is the basis for the topographic contour lines. We can set the computer to generate 1 foot or 2 foot incremental contours, depending on the size and slope of the property. The rainbow lines show the surface grid, and the grey lines show the generated contour lines.
Remember, each point has an x,y,z coordinate, the z axis being elevation. As the head of the machine rotates around 360 degrees, it also "looks" up or down. When we set up the machine, we measure it's exact distance to the ground. We also have an exact measurement from the prism to the ground. The computer calculates these distances and factors them into the distance and vertical angle measurement for each point to give an z axis value, or elevation.
To create contours, we simply take multiple elevation points on the ground to generate a grid or polygonal surface. Then we use a computer algorithm to calculate contours based on this surface. Therefor, you can imagine that the contours are an approximation, usually accurate within a foot. This is good enough for most design purposes and is used to give the designer an idea of aspect, slope, water flow, and grading requirements.
A Licensed surveyor, however, will use either a GPS unit, or will locate points called benchmarks which give reference to the rest of the world using latitude, longitude, and elevation coordinates that have been placed within a datum. I'm not going to go too much into detail about what is a datum, but basically it is a system for approximating the curvature of the planet and projecting curvature onto a flat surface.
Like all other points we make in a map, the elevation coordinates we use to create contour lines are relative to the base point we created in the beginning to backsight our machine. Therefor if you wanted to have the elevation be represented in height above sea level, you would need to backsight to a point with a known correct elevation, latitudinal, and longitudinal coordinates. Likewise, if you want your map to be correctly placed within a global coordinate system, you would need to backsight to a point that geographically referenced, such as a bench mark.
When a lisenced surveyor backsights to one of these points, this is called geo-referencing, and it places the map in the right place relative to the rest of the world. This is especially important for establishing legal boundaries, and building roads or other projects that stretch over very long distances. At Foresite, we don't find that it is necessary for most design purposes to geo-reference.
In some spots, like nooks along the wall of a structure, or other places where sight lines may be obstructed, we will revert back to the good old fashion way of taking hand measurements. Distances are calculated using a tape measure, and angles can be calculated by a process called triangulation.
Building walls are the easiest to measure because most structures are built with 90 degree angles.
Lets say that you are trying to locate the trunk of a small tree, and you just don't have the sight line from your machine, so you will have to triangulate using a tape measure.
In the diagram above, the orange lines represent your measurements taken with a tape measure, and where they meet is at the center of the tree trunk. From the tree to the corner of the workshop building is let's say 31. 48 feet, and from the corner of the house it is 15.25 feet. Because you already have recorded the corners of these structures, you can deduce the location of the third point from these 2 distance measurements. The pink circles in the diagram coming from the corners (this is a quick sketch, so forgive that the circle is not exactly centered on the corners) can be drawn on the map with the exact radius of the measurements taken. So the larger circle from the workshop corner is 31.48 feet, and the smaller circle is your measurement of 15.25. Where the circles intersect, you have your triangulated point. There are only 2 intersections, and therefor there are 2 possiblities of where the point is, however, you will take note of the approximate location of the object and will be able to tell which intersection to use. Alternatively, you could measure from a 3rd point, and this would narrow your intersection down to 1 point only.
Hand Measuring Elevations
Once you have triangulated the x,y coordinates of a point, you may also need to record it's relative elevation, or z coordinate. To measure elevations, you will need a line level, a string and a tape measure. When hand measuring elevations, just like x,y coordinates, it is a relative mesurement to other known points. In other words, you are measuring the elevation distance between point a and point b and using that to find relative elevations throughout the map
Once it is tied to your relative elevation point (point a), pull the string tight, use the line level to make sure it is level, and measure the distance from the string to the new point you are measuring (point b). If the string is tied 1 foot above your relative elevation point, make sure to factor that in. You can use the same relative elevation point now to measure to multiple other points (points c, d, e, and f can all be measured from point a)
By combining the above methods, it is actually possible to measure an entire property by hand, although it will be much more time consuming and not as accurate as using a total station.
Using CAD to Format a Layout
The process of formatting is an interesting subject, so keep your eye out for a more detailed article about this yet to come.
Customization and End Product