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Les images Wayback et les métadonnées Wayback ne correspondent pas, une explication ?

Hornbydd

J'accède aux images Wayback pour mettre à jour un ensemble de données des fronts glaciaires en Géorgie du Sud. ArcPro et les images Wayback offrent un ensemble de données pratique pour numériser, mais UNIQUEMENT si vous connaissez la date de l'image.<\/P>

C'est pourquoi j'accède également aux métadonnées Wayback équivalentes pour la même version des images.<\/P>

Je sais et m'attends à ce que certaines images que je vois datent en fait de quelques années plus tôt et que world imagery n'a pas encore été mis à jour avec de nouvelles images, cela a du sens et je pense que c'est acceptable.<\/P>

C'est quand il indique d'une manière ou d'une autre le futur que je deviens très méfiant ! Cela sape la confiance dans ce que je regarde réellement. Quelqu'un de l'équipe esri imagery peut-il expliquer pourquoi je vois ce que je vois ci-dessous ?<\/P>

J'ai activé 2019 (r00) ainsi que ses métadonnées équivalentes 2019_r00. J'ai l'ensemble de données historique des fronts glaciaires montrant une partie d'un bord de 2003 sélectionné. Les données de 2003 ont été capturées avec landsat 7. Notez que le bord de 2003 s'aligne parfaitement avec les images Wayback de 2019.<\/P>

Maintenant, mon petit cerveau me dit que world imagery de 2019 n'avait pas été mis à jour et montre donc des images de 2003. Cela aurait un sens logique, sauf que si vous regardez la fenêtre contextuelle à droite, les métadonnées indiquent une image de 2024, soit 5 ans dans le futur<\/EM> ?<\/P><\/span><\/P> <\/P>

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Accepted answers

JeffreySwain

Hi Duncan,

For that tile layer, if you are searching for the collection date of that imagery, then you can trust that the 2019 tile layer contains imagery from 2019 and so on for each of the tile layers. However, if you are researching on the acquisition date for a particular dataset within that dataset, other than the listed year in the set you will not find it with those fields. If you want specific dates, I would consider the Living Atlas Sentinel 2a Level 2 or Landsat imagery layers for specific dates.

Both have 'Acquisition date' fields that you can trust.

All comments

JonM32

@DuncanHornby

Hi Duncan - you may have some better luck sorting out the metadata by referring to the app below. I used it lately to figure out when and why the imagery in my area changed. The metadata seemed to be up to date. It looks like you may be using the same thing in Pro already though.

Wayback App - https://livingatlas.arcgis.com/wayback

Hornbydd

Hi Jon,

Thanks for the pointer to the website, I explored this and the info box that pops up provides even less detail than the metadata layer when loaded in ArcPro. So it does not resolve my query. Useful website for quickly checking imagery.

Duncan

JonM32

No problem. Out of curiosity, what rest service are you accessing the wayback imagery and metadata from in Pro?

Hornbydd

For the metadata the url was - https://metadata.maptiles.arcgis.com/arcgis/services

For the imagery the url was - https://wayback.maptiles.arcgis.com/arcgis/rest/services/World_Imagery/MapServer

StephanieDockstader

Hi Duncan, Thanks for your question. I have sent this to our product eningeering team to review. I will post thier response here once I get some additional details.

Thanks,

--Stephanie

JeffreySwain

Hey Duncan,

I went in and was looking into your issue and there are a few things to discuss. So first since you are using the World Imagery layer you need to understand that while it shows imagery it is a tile layer.

So what you are reviewing is the metadata of the tiles, not the source imagery. So when a tile layer is created, 'tiles' based on the source imagery are created. So the metadata you are looking at refers to the creation of the tiles rather than the source imagery. That metadata is updated each time the tiles for that tile layer are updated which happens periodically.

If you are interested in pixel values and the source imagery, then be sure to select an Imagery layer like this one - US NAIP Imagery layer.

Once an imagery layer like that is added to ArcGIS Pro, you can use the Raster Item Explorer.

Hope this helps.

Jeff

Hornbydd

Hi Jeff,

Thanks for finding time to help me understand the data.

So using my example in the original question, am I correct in saying that the way back images were archived in 2019 and that knowing from the glacier dataset I have it was showing a 2003 image when it was archived. But since then the tile layer has been rebuilt and has overwritten (?) the original source image date with 2024 date? Would that mean as a user I can never truly know what the source image date is as the metadata is reporting the built date of the tile layer?

Or have I got the wrong end of the stick?

JeffreySwain

Hi Duncan,

Hornbydd

Hi Jeff,

Thanks for pointing me to the sentinel 2 imagery layer. This is indeed giving me that much needed acquisition date. It's a shame that the wayback data does not seem to keep that, as the quality of those images are very good. May be moving forward, future versions of the wayback metadata could provide such information? I can only but hope!

Duncan

JeffreySwain

Hi Duncan,

All of the layers in ArcGIS Online have upsides and downsides and can be used for very different purposes. For the Wayback imagery, the tile layers perform exceptionally well and look amazing. For the purposes of the Wayback machine, they perform amazingly. The app visualizes what once was so tile layers work exceptionally. For more analytical purposes, imagery layers provide pixel values and source metadata. So the wayback machine has performed its purpose as the start of your analysis and led you to other research options.

I hope your research works out and if you have any other questions feel free to message me on the Esri Community app.

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