RETROCHANGE - UC4 / RETROCANOPY EXAMPLE DATA
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This directory supplies the Havešová worked example for historical
canopy-gap analysis in an old-growth beech forest in Poloniny National
Park, Slovakia. It contains a KH-9 HEXAGON image from approximately
1975 and one manual gap correction.

FILES
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Havesova.tif
    Historical grayscale image, 3,681 x 3,079 pixels, 0.5 m sampling,
    UInt8, EPSG:5514, NoData = 255. It is clipped to the study area
    using NoData outside the valid image footprint.

add_gaps.shp / .shx / .dbf / .prj / .cpg / .qix
    One hand-drawn gap polygon, approximately 547.39 m2 (0.05474 ha).
    It adds an opening missed in the Havešová worked example. Keep
    all supplied components together under the add_gaps base name.

LICENSE.txt
    Dataset license, source acknowledgment, and citation requirements.
METADATA.txt
    Raster properties, study-area coverage, correction provenance,
    and interpretation limits.
README.txt
    This overview and usage instructions.

COVERAGE AND NODATA
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The image's rectangular footprint covers 283.344975 ha, but only
144.70925 ha (5,788,370 pixels) have values other than NoData 255.
Use the valid image area, approximately 144.7 ha, as the study-area
denominator. Do not count the surrounding NoData as closed canopy
or as a gap. Preserve the raster's CRS and NoData declaration.

The 0.5 m output grid is a sampling interval, not a positional
accuracy estimate or a statement of original sensor resolution.

RUNNING THE HAVEŠOVÁ EXAMPLE
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1. Keep this data directory beside the application notebook.
2. From the uc4_retrocanopy application root, open
   Poloniny_canopy_gaps_1975.ipynb.
3. Retain the default settings to reproduce the supplied example:
       SRC = DATA_DIR / "Havesova.tif"
       ADD_GAPS = DATA_DIR / "add_gaps.shp"
       GAP_MIN_AREA_M2 = 20
4. Run the notebook and inspect the threshold diagnostics and
   mapped candidates before interpreting the summary statistics.

The Poloniny canopy gaps notebook and its supporting documents belong
to the UC4 / RETROCANOPY package. Use the filenames above when opening
files or setting paths.

For a new study area, supply an image clipped with a correct NoData
mask, update SRC and LABEL, and set ADD_GAPS = None unless you have
corrections for that new area. The supplied polygon belongs only
to Havešová. It is not an independent validation sample.

Guides, relative to this data directory:
../docs/retrocanopy_guide.md
../docs/canopy_gaps_1975_reading_version.html

Environment definitions:
../env/environment-canopy-gaps.yml
../env/requirements-canopy-gaps.txt

INTERPRETATION AND LIMITATIONS
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The source is an image, not a ready-made gap map. The notebook derives
candidate openings using an explicit detection rule and optional
manual corrections. Image shadows, threshold choice, minimum mapped
area, and interpretation affect the result. Report those settings
and whether the hand-drawn polygon was used.

The manual polygon's geometric area need not equal its contribution
to final gap area after rasterization, overlap, clipping, and cleanup.
Results from this worked example do not establish detection accuracy
for other forests, images, or dates. One image supports a historical
baseline; temporal change analysis requires comparable observations.

SOURCE, LICENSE, AND CITATION
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Historical source: Declassified KH-9 HEXAGON imagery, USGS EROS,
approximately 1975. The package does not identify an exact acquisition
date or source scene. Data preparation and distribution: Technical
University in Zvolen, RETROCHANGE project.

The derived data and documentation are supplied under CC BY 4.0 to
the extent of rights held by the Technical University in Zvolen.
See LICENSE.txt for details. Retain the documentation with the data.

Technical University in Zvolen (2026).
RETROCHANGE UC4 RETROCANOPY Havesova 1975 Image and Gap Correction.
RETROCHANGE project. https://gis.tuzvo.sk/retrochange

Technical University in Zvolen
T. G. Masaryka 24, 960 01 Zvolen, Slovakia
