Easting Playground — request builder

modelstring

meridian-2026-04

streamboolean

false

system_promptstring

You are a field-notes assistant for survey crews. You answer in plain language, keep units explicit, and state the datum you assumed.

historyarray of objects

User

Which vertical datum does the county benchmark sheet use?

Assistant

Sheets issued after 2019 quote orthometric heights, not ellipsoid, on every sheet.

Add object

messagestring

How do I convert an ellipsoid height to an orthometric height?

Append this exchange to the history array

Reset

Run

Python

Node

cURL

REQUEST

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1curl --request POST \
2  --url https://api.easting.dev/v1/chat \
3  --header 'accept: application/json' \
4  --header 'content-type: application/json' \
5  --header 'authorization: bearer est7QpV2mLcRAdN4hUyBvKt9Rw3Xz
6  --data '{
7  "message": "How do I convert an ellipsoid height to an ortho
8  "model": "meridian-2026-04",
9  "system_prompt": "You are a field-notes assistant for survey
10}'

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"response_id": "4c81a7e2-96b3-4f1d-a70e-d99badca20da",
"text": "Ellipsoid height and orthometric height answer two
different questions, so converting between them means
introducing a third surface. Here is the short version: 1.
**The three surfaces:** - The ellipsoid is a smooth
mathematical figure your receiver reports against; it has no
physical meaning on the ground. - The geoid is the equipotential
surface that mean sea level approximates, and it is the one a
spirit level follows. - Orthometric height is measured from the
geoid, which is why it is the height that governs how water
moves. 2. **The relationship:** h = H + N, where h is the
ellipsoid height your receiver logged, H is the orthometric
height you want, and N is the geoid separation at that
coordinate. 3. **Getting N:** - Pull it from the published
geoid model for the region rather than interpolating by hand.
- Sample it at the point itself; over a 3 km traverse the
separation can drift by more than a decimetre, which is