Tree and building heights from lidar, across Oregon

Who uses this

• Arborists and foresters. Screen tree heights across a property or a stand.
• Planners and neighbors. Get approximate building and tree heights for a shading or view question.

When to use it

• Checking tree heights for shading, view or line-of-sight questions.
• Getting approximate roof heights across a neighborhood.
• Seeing what stands on a property before visiting.

Tools for your job

Object Heights is one step in a bigger question. These are the jobs it helps with, and the tools that go with it.

How to use it

1. Select a property, draw an area or upload a boundary.
2. Run. Heights are drawn from tan (nothing above ground) to deep blue (tallest).
3. Read the coverage, the minimum, mean and maximum in the panel. For ground elevation use Terrain Stats instead.

Step by step: Mount Hood

We measure the forest and buildings around Timberline Lodge from DOGAMI’s lidar surface model.

1.Zoom to the area and run the analysis. Tan is bare ground, deep blue the tallest objects. The panel shows the mean and maximum height above ground.

2.Zoom in and single roofs and trees stand out. The panel warns what share of the area is steeper than 30°, where the readings are less reliable.

What it showed

• Buildings and trees are not told apart; compare with the aerial basemap.
• Heights are from when the lidar was flown. Trees planted or cut since do not show, and areas the surface mosaic does not yet cover come back blank.

How it works

Lidar produces two models: the bare earth with everything stripped off, and the surface, which is the top of whatever the laser hit first. Subtracting one from the other, cell by cell, leaves the height of trees, buildings and other objects.

Cells with no surface data, an obvious no-data value, or a surface below the ground are left blank. The color scale is stretched between the 2nd and 98th percentile so a single tall tree does not wash out the rest.

Reading the results

Values are feet above the ground, not elevation. A low reading in a field is a fence line or a hedge; a reading over 100 ft is a mature conifer.

Buildings and vegetation are not told apart. Use the aerial basemap to see which is which.

Limits and caveats

• Only where DOGAMI’s surface model has data, and only as things were when the lidar was flown. The mosaic is still being completed, so parts of the state are blank.
• Over cliffs, rock outcrops and snowfields the two models diverge for reasons unrelated to objects. The tool warns when most of the area is steeper than 30 degrees, and readings there should be ignored.
• The surface and bare-earth models can come from different years in the same area. DOGAMI also notes a half-pixel (1.5 ft) horizontal shift in its mosaics, which can show as a thin fringe along building edges.

Data and attribution

Results come from the USGS 3D Elevation Program (3DEP) bare-earth elevation model: lidar at 3.3 ft per pixel where it has been flown, and the 1/3 arc-second model, about 33 ft per pixel, elsewhere, with elevations above NAVD 88. The tools with a surface option (Sunlight, Viewshed, Sightline, Object Heights) read DOGAMI’s statewide digital surface model of trees and buildings.

USGS 3DEP elevation data and USGS maps are U.S. Government works in the public domain: you may use the results, including commercially. A credit to the USGS 3D Elevation Program is appreciated, and every file you download carries it. DOGAMI lidar products are published by the State of Oregon; credit "DOGAMI / Oregon Lidar Consortium". County taxlot boundaries are the assessor's GIS data, not surveys, and each county publishes its own disclaimer, shown with the parcel. The aerial basemap is from Esri and follows Esri's terms; it is not included in downloads.

Questions

Related

Related tools

• Terrain Stats — Summarizes the minimum, maximum, mean and range of ground elevation across an area, with a chart of how much land sits at each elevation.
• Sunlight — Models hours of direct sun across a site on any day of the year, with shadows from terrain up to 1.86 mi away and, where DOGAMI’s surface model exists, from trees and buildings.
• Viewshed — Shows which ground can be seen from a point, out to a radius you pick from 0.5, 1, 2 and 5 miles, for a chosen eye height, with earth curvature and refraction allowed for and, optionally, trees and buildings blocking the view.