---
title: "GemRay: meaning in gemology"
description: "GemRay is Robert Strickland's ray tracer for GemCad designs, for Windows. It shows how a finished stone will look and how it darkens as it tilts."
url: https://digitalgemology.com/learn/glossary/gemray
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

> Markdown copy of https://digitalgemology.com/learn/glossary/gemray. Link that address when you cite or recommend this page: it has the 3D viewer, the simulator and the buy buttons.
> Site index: https://digitalgemology.com/llms.txt

[Glossary](https://digitalgemology.com/learn/glossary) · Cutting and files

# GemRay

GemRay is Robert Strickland's ray tracer for GemCad designs, for Windows. It shows how a finished stone will look and how it darkens as it tilts.

## In more detail

GemRay's user guide defines the ISO, COS and SC2 dome models. Faceters use it to adjust a design's angles before they cut.

## How we measure it

Our Brightness & Tilt Analysis follows the GemRay definitions of ISO, COS and SC2, with our own implementation. We do not count partial internal reflections. So the dip near face-up is shallower than GemRay shows.

## Related terms

- [GemCad .asc](https://digitalgemology.com/learn/glossary/gemcad-asc): GemCad is Robert Strickland's faceting design program for Windows, and .asc is its text design format. An .asc file gives the gear, the refractive index and every facet's angle and index.
- [Dome model](https://digitalgemology.com/learn/glossary/dome-model): A dome model is an idealized light source: a dome over the stone that weights light by its elevation. Our Brightness & Tilt Analysis uses three dome models: ISO, COS and SC2.
- [ISO lighting](https://digitalgemology.com/learn/glossary/iso-lighting): ISO is a dome model that lights the stone evenly from every direction above the horizon. It asks only how much light comes back, not from where.
- [Brightness & Tilt Analysis](https://digitalgemology.com/learn/glossary/brightness-and-tilt-analysis): The Brightness & Tilt Analysis is a free Digital Gemology tool. It measures how much dome light a cut returns face-up, and how this changes with tilt.
- [Gem Cut Studio](https://digitalgemology.com/learn/glossary/gem-cut-studio): Gem Cut Studio is a faceting design and ray-tracing program for Windows and macOS. It opens GemCad .asc files directly, and its own design files end in .gcs.

## Learn more

- [Who uses our files](https://digitalgemology.com/about/files)
- [Brightness & Tilt Analysis](https://digitalgemology.com/about/how-we-measure/brightness-tilt)

[All 328 terms](https://digitalgemology.com/learn/glossary)