How to Measure an Obstacle for a Shadow Estimate

Collect practical height, width, position, and orientation inputs for a building, wall, or tree before using a shadow calculator.

Last reviewed September 18, 2026

A precise solar position cannot rescue an inaccurate obstacle. The strongest improvement to a local shadow estimate is usually better scene geometry, especially height and distance from the receiving point.

Identify the part that actually blocks the sun

Measure the relevant roof edge, parapet, wall top, or tree crown rather than a generic property height. A stepped roof may need more than one simplified obstacle. Use the map footprint to place each blocker on the correct side of the receiving point.

Obstacle height: elevation of the blocking top above the shared ground datum. Enter receiver height separately; for a top 15 m above ground and a receiver 5 m above that same ground, enter 15 m and 5 m, not a 10 m obstacle height.
Width: the horizontal span visible from the receiving point.
Position: coordinate or map placement of the obstacle center.
Rotation: the vertical screen’s normal, clockwise from true north.

Prefer documented measurements

Plans, surveyed elevations, manufacturer dimensions, or a reliable site measurement are stronger than visual guesses. For a rough field estimate, a measured horizontal distance and elevation angle can be converted to height, but document the instrument and uncertainty.

Do not treat a map footprint as proof of height. Open map data can establish context while the user-supplied dimension remains the declared assumption.

Model trees as ranges, not exact solids

Tree shade changes with crown shape, foliage, pruning, wind and season. SunCarta currently treats a tree as an opaque vertical screen; vary measured height and width as sensitivity tests, then verify actual canopy shade. It does not simulate leaf transmission.

Record uncertainty beside the result

Keep the source and date for every important dimension. If a building height is only estimated, compare a reasonable low and high case. A conclusion that survives both cases is more useful than a single over-precise output.

Questions about this method

Can satellite imagery provide building height?

Ordinary overhead imagery usually provides footprint context, not a verified height. Use a documented elevation source or a measured estimate and keep its uncertainty visible.

Should roof overhangs be a separate obstacle?

An overhang can block high-angle sun, but the current vertical-screen model does not represent a horizontal slab. Record it as unmodeled and check it on site rather than entering a misleading wall.