How Linework Features are Marked
We adjust the density of points depending on the terrain. We will never use less than approximately a 30’ distance between points, but will increase point density as required to appropriately represent the real terrain.
In areas of sparse vegetation where patches of bare earth are visible, the bare earth portions will be marked, and the topographic points will be labeled as standard topo points.
In areas of moderate vegetation where there are no areas of bare earth clearly visible, the lowest elevation points in the area will be marked, and the topo points will be added in the vegetated topo points layer.
In areas of dense vegetation where no reliable terrain information can be derived (i.e. dense tree cover), then a polygon of “unreliable information” will be drawn surrounding that area.
Breaklines will be added in a density required to faithfully represent the terrain in real life. In areas of significant noise (i.e. dirt roads with numerous tire ruts) a density of no more than 4 parallel breaklines per 10 horizontal feet will be drafted.
Curbs are captured with 2 lines in 3D, the Edge of Pavement and the Back of Curb. It is advised to offset from those two lines to get the rest of the curb geometry. When Edge of pavement is not present, the drafter may use a breakline to represent the curb geometry. All curbs will have 2 lines that represent its geometry.
The crown of a road is mapped and marked as a breakline where a clear crown is visible. For roads where the exact crown is not clearly identifiable in the 3D model, a breakline will be drawn along the approximate center of the road.
Building footprints cannot be reliably marked from photogrammetry data. Instead, we mark the dripline of any building that is present in the linework.
When lines go under trees / eaves, wherever possible, we will continue the breakline interpolated underneath the tree. It is possible that there is error when interpolating lines, as the line may not continue in real life. For gaps of 20’ or greater, we will not interpolate underneath the gap but will leave it blank.
In areas with slight to moderate damage to concrete, asphalt, or other hardscape, the drafting will represent what the ideal concrete line would have been, not every individual piece of damage, unless otherwise requested. For significant road damage (>3’ damaged or more) then drafting will follow the actual, damaged line.
Utility access panels are marked with a single point at the elevation of the panel itself. Because it is impossible to tell from the air what type of utility it is, they are all marked in a “utilities” layer.
Larger utilities (more than 2 feet across) will be marked with 3D polylines.
Fire hydrants are marked with a single point in a fire hydrant layer. This is marked as a 2D feature.
Storm drains are marked with a 3D polyline / polygon surrounding the drain itself.
Lamp posts, lighting fixtures, and power poles are marked with a single 2D point at the point where the pole meets the ground.
Brick walls, concrete walls and fences are captured in 2D with one line down the center. Any elevation change, such as with a retaining wall, is captured in 3D with breaklines.
Shear faces and walls are captured in 3D with a top and toe breakline. Please note that data at the bottom of a shear wall or face can be unreliable due to the limitations of photogrammetry and may not be captured if the drafter determines that it is unreliable data.