Copy of AgGateway Post-Image Collection Specification (PICS)
This page will house the deliverable (an implementation guideline) for AgGateway's PICS project.
November 21 update: The PICS team is actively working on the text of the implementation guideline. Please check back soon, but meanwhile, please take a look at the informative flyer:
Preferred Image Format:
Why GeoTIFF?
GeoTIFF meets the projection requirements
Other Benefits:
- Compression
- Radiometry
- Transformation
- Public domain metadata standard (for encoding/decoding)
- Open Source component GDAL plugin (MIT license)
- Possible to include aux/sidecar files
GeoTIFF Specifications
- GeoTIFF v 1.0 - http://web.archive.org/web/20160403164508/http://www.remotesensing.org/geotiff/spec/geotiffhome.html
- TIFF 6.0 specifications - http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
Known Limitations:
- 4GB limit, to be remedied by using the proposed BigTIFF format - http://bigtiff.org/
- Anything larger than 4GB needs to utilize BigTIFF specifications
- Can also be solved by breaking large tiff files into 4GB tiles and using virtual layers
Additional Tags Required:
GeoTIFF does not supply all the tags necessary to define information such as spectral band width, band center wavelength, name or acquisition time or duration. Using both the EXIF and XMP tags shown below the PICS requirements can be satisfied.
| Item | Tag Type | Key | Example | Type | Notes | Link to Specification |
|---|---|---|---|---|---|---|
| Band Name | XMP | Xmp.Camera.BandName | {"Red", "NIR"} | XmpSeq | Name of each band (sequence). Single page image: one name for each band of the image. | https://support.pix4d.com/hc/en-us/articles/206434245-Camera-XMP-Specification#gsc.tab=0 |
| Band Center Wavelength | XMP | Xmp.Camera.CentralWavelength | {660, 800} | XmpSeq | Central wavelength of each band in nm. Similar to band names. If band names are not defined, default band names are generated. | https://support.pix4d.com/hc/en-us/articles/206434245-Camera-XMP-Specification#gsc.tab=0 |
| Band Width | XMP | Xmp.Camera.WavelengthFWHM | 16015 | XmpSeq | Full width half maximum of the wavelength distribution in nm. | https://support.pix4d.com/hc/en-us/articles/206434245-Camera-XMP-Specification#gsc.tab=0 |
| Acquisition Date | EXIF | Exif.GPSInfo.GPSDateStamp | 2016:03:01 | Ascii | Mean GPS date (UTC) | https://support.pix4d.com/hc/en-us/articles/205732299#gsc.tab=0 |
| Acquisition Time | EXIF | Exif.GPSInfo.GPSTimeStamp | 12/1 8/1 54785/1000 | List of Rational | Mean time of capture - GPS time as hour, minute, second (UTC), with sub-second accuracy | https://support.pix4d.com/hc/en-us/articles/205732299#gsc.tab=0 |
| Acquisition Duration | XMP | Xmp.Camera.AcquisitionDuration | 23456 | XmpText | Time taken to acquire all images in dataset, measured in seconds | Pix4D - proposed |
| Versioning | GeoTIFF | 65265 | <?xml version="1.0" encoding="UTF-8"?> | Ascii | This is using the PAIL schema to accomplish recording a version. | Proposed |
Other Image Formats:
GeoTIFF was selected as a preferred format for many reasons, but primarily because it is adaptable to so many projections and flexibly for re-projection makes it desirable. It is not recommended but the EXIF and XMP tags outlined can also be used with other image formats such as ".jpg" or "png" but these other formats may lack projection unless a sidecar/auxiliary file is used.
A tiny link to this page is: https://aggateway.atlassian.net/wiki/x/XABrDw and a tiny-er link: http://bit.ly/2z90aeD
The tiny-link-bearing QR code: