How to Access Photos from ODK Aggregate with a MySQL Database?

Question

We have installed OpenDataKit (ODK) Aggregate and we are using a MySQL Database. I can see the data inside the _PHOTO_BIN, _PHOTO_BN, and PHOTO_REF tables - but how do I read this data and display the image? I see in the _PHOTO_BN table there is a field named UNROOTED_FILE_PATH which contains a .jpg filename, but I don't know if this can actually be used to access the image?

Thank you.

Answer 1

This answer was give on the ODK Google Groups site

The easiest way to access the images is through the ODK Aggregate URL for accessing attachments.

The database tables are structured so that unbounded-size images can be stored in the database. If your image size is under 1 MB, it is stored in one data record, but if you have larger image files (or longer streaming videos), they are split across multiple blob records, and writing the logic to reconstruct them will be error-prone.

The ODK Aggregate URL for, e.g., the GeoTagger form on opendatakit.appspot.com, looks like: http://opendatakit.appspot.com/view/binaryData?blobKey=geo_tagger_v2%...

If you want a small thumbnail, specify previewImage=true (as above).

If you want to download it as an attachment (or access the original filename), you can also specify as_attachment=true, in which case it will supply the filename as originally uploaded.

The blobKey identifies the image. As with all URLs, the parameters are URLEncoded which makes them very ugly. The URLDecoded blobKey looks like:

geo_tagger_v2[@version=null and 
@uiVersion=null]/geotagger[@key=uuid:f6454ba6-2485-426f-8e1a-8981e463e6fe]/ Image

This is an XPath-style naming for the image element in the Xform. It identifies the form id: get_tagger_v2, the version and uiVersion values (from the attributes on the Xform's top-level element), the name of the top-level element in the form (geotagger), the primary key for the submission being referenced (uuid:f6454ba6-2485-426f-8e1a-8981e463e6fe) and the XPath within the form to the image. In this case, the image (field name Image) is immediately underneath the top-level element in the form.

If you had repeat groups, you would have to specify the ordinal (1..n) of the repeat group. So for the first repeat group, you would have:

.../repeatElement[@ordinal=1]/Image

and for the 5th repeat, you would specify:

.../repeatElement[@ordinal=5]/Image

Mitch