InSite SiteWork and Field General uses a patented algorithm technique based on Delauney Triangulation to generate the Existing, Proposed, and underground strata surfaces. In plain English, it is simply the most accurate method available for surface generation, and gives the most accurate sitework quantities. If you are curious about the InSite's advantages, read on!

A surface can be entered into InSite SiteWork as spot elevations, contours, or sloping lines (think contour, but where each point along the contour has a different elevation), or a combination of all three. As you can see in the simplified drawing, a single spot shot will "spider web" to adjoining contours or other spot shots. There is no need to connect spot shots together with sloping lines.

The elevations for calculation are taken from the plane created by each triangle. It is easy to see at a glance how InSite interprets the data. Once the surfaces are generated, InSite Uses the Grid Method to generate the earthwork volumes. Take-off systems which use Average End Method, or systems that do not triangulate, require the spot elevations to be connected with sloping lines, which increases the take-off time.

Contouring programs and Machine Control programs also use triangulation files.

Grid Method vs. Average End Area Take-off

The grid method is the method most commonly used by estimators for manually determining the required cuts and fills from contour maps. Its accuracy and reliability has been proven by years of experience and actual load counts.

In spite of this, one vendor of earthwork estimating software, which uses another method, has chosen to mount a publicity campaign to discredit the grid method. Even though most experienced estimators realize from common sense that it is not credible to suggest that the method they have relied on and gotten good results with is suddenly no good, many have asked for an analysis of the two methods.

In the grid method, the map of interest is divided into many evenly spaced rectangles by parallel and perpendicular lines. Each small rectangle is known as a grid square. For estimating purposes, each grid square is assigned an existing and a proposed elevation. The difference of the two elevations multiplied by the area of the grid square is the cut or fill volume associated with that grid square. Adding up all the grid squares on the site gives the totals for cut and fill.

The elevation to be assigned to a grid square is determined by interpolating between the TIN (triangular irregular network) formed from all known elevations on the site. The accuracy of the estimate is determined by the size of the grid square.

InSite SiteWork allows grid squares as small as 1 foot on a side, so that every point on the map is within .5 feet of a grid point. When you consider that existing contours are generally interpolated from field data on a 50 foot or larger grid, you will realize that the grid method used for take off is more accurate than the original survey data. Since the accuracy of the final result is only as good as the least accurate step, then a properly applied grid take off will be as accurate as the map that was used.

The Grid method is sometimes criticized because of the fact that subgrade boundaries are slanted lines between grid points. If the grid size is chosen appropriately, this is not of particular concern because in fact subgrades are not usually excavated exactly vertically, and never exactly on a building perimeter. In any case, the slightly slanted side between grid points gives the same answer, on average, as a vertical line. As further insurance of accuracy, InSite SiteWork calculates subgrade boundaries (parking lots, building pads, etc) using a grid 1/4 the size of the grid for contours, down to .25 feet.

The average end area of cross sections method is sometimes used by engineers and general contractors who want a quick site balance, but who don't need the detail and accuracy required by excavating contractors. The procedure is to draw cross-sections at various points across the site. The areas of each pair of adjacent cross- sections are averaged and multiplied by the distance between to obtain volumes for existing and proposed. The volume for proposed is subtracted from the volume for existing to obtain the fill (+) or cut (-) amount.

One earthwork program that uses this method calculates a cross-section through each user-entered data point. The supposed advantage of this method is that the cross-sections actually pass exactly through all the data points. This is true. However, a big problem is that in the direction perpendicular to the cross-sections, large sections of map may be averaged. It is necessary for the program user to know how to space the input points to obtain a reasonable result. It is interesting to note that the designers of that program saw this as enough of a danger that they have the program switch to running cross-sections on a grid whenever the user does not remember to enter enough points.

InSite SiteWork uses grid method. In the early stages of designing InSite SiteWork, all methods were considered and tested. Testing was done in comparison to a calculation using the Triangular Irregular Network (TIN) method, which is recognized as providing all of the accuracy that is available in any set of data points. Our conclusion was that only the grid method gave consistent accuracy without requiring special knowledge on the part of the user.

All publishers of earthwork software know that the only real accuracy concern is whether the user correctly entered the map, although some would rather not talk about it. If a program is difficult to use, or if the input is difficult to verify, then the inevitable human errors may not be caught before it is too late.

At InSite Software, we have specifically oriented InSite SiteWork for accuracy, ease of use and ease of verification.