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Add GeoTransform as implemented by GDAL #19

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merged 6 commits into from
Nov 4, 2024
Merged

Add GeoTransform as implemented by GDAL #19

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54029c4
Add GeoTransform as implemented by GDAL
dblodgett-usgs Apr 12, 2023
49e0313
fix usage of "Auxiliary"
dblodgett-usgs Apr 13, 2023
600ce8d
update per discussion in #17 -- numeric not ascii
dblodgett-usgs Apr 15, 2023
195edc9
better align with GDAL raster data model.
dblodgett-usgs Apr 26, 2023
78b0ed7
add row counting from 0
dblodgett-usgs Apr 26, 2023
9bce071
and columns.
dblodgett-usgs Apr 26, 2023
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9 changes: 8 additions & 1 deletion geozarr-spec.md
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Expand Up @@ -30,7 +30,7 @@ GeoZarr DataArray variable MUST include the attribute **\_ARRAY_DIMENSIONS which

### GeoZarr Coordinates

GeoZarr Coordinates variable is a one dimensional **Zarr Array** that **indexes a dimension** of a GeoZarr DataArray (e.g latitude, longitude, time, wavelength).
GeoZarr Coordinates variable is either a one dimensional **Zarr Array** or an empty **Zarr Array** containing a **grid_mapping** which includes a **GeoTransform**. In both cases, the coordinates **index a dimension** of a GeoZarr DataArray (e.g latitude, longitude, time, wavelength).

GeoZarr Coordinates variable MUST include the attribute **\_ARRAY_DIMENSIONS equal to the Zarr array name** (e.g. latitude for the latitude Zarr Array).

Expand Down Expand Up @@ -75,6 +75,13 @@ The following standard names are recommended to describe coordinates variables f

The **grid_mapping** CF variable defined by DataArray variable defines the coordinate reference system (CRS) used for the horizontal spatial coordinate values. The grid_mapping value indicates the Auxliary variable that holds all the CF attribute describing the CRS.

In GeoZarr, the grid_mapping variable can contain a **GeoTransform** attribute. A GeoTransform is a vector of six double precision digits: [X_offset, X0, X1, Y_offset, Y0, Y1] `X_offset` and `Y_offset` are the grid origin. `X0` and `Y0` are the grid spacing per column. `X1` and `Y1` are the grid spacing per row. If `X0 = Y1 = 0`, the grid is axis aligned. In GeoZarr, coordinates are always always aligned with a cell center and it is left to a data user to decide if values are constant across a cell or valid only at the precise cell cetner. The following equations can be used to create derive georeferenced cell centers.
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```
X_georeference = X0 * column + X1 * row + X_offset
Y_georeference = Y0 * column + Y1 * row + Y_offset
```

### Other CF Properties

All other CF conventions are recommended, in particular the attributes below:
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