# Add access to jacobi of cell through ufl.

Something like this:

J = cell.J # d x d tensor with Jacobi of geometry mapping

detJ = cell.detJ # isn't this the same as the already existing cell.volume?

Should be easy to add for form compilers as well, this information should already be computed in tabulate_tensor.

## Blueprint information

- Status:
- Complete

- Approver:
- None

- Priority:
- Medium

- Drafter:
- None

- Direction:
- Needs approval

- Assignee:
- None

- Definition:
- Obsolete

- Series goal:
- None

- Implementation:
- Unknown

- Milestone target:
- None

- Started by

- Completed by
- Martin Sandve Alnæs

### Whiteboard

Old geometry types:

triangle.x

triangle.n

triangle.volume

triangle.facet_area

triangle.

triangle.

New geometry types already added to UFL:

triangle.xi # Local cell coordinates (not always available, raise suitable error otherwise)

triangle.J # Jacobi of geometry mapping

triangle.Jinv # Inverse of J

triangle.detJ # Determinant of J

### Work Items

Work items:

Adding expression types: DONE

Adding cell properties: DONE

Updating algorithms in UFL: TODO

Updating algorithms in form compilers: TODO

Generating code in form compilers: TODO

Eventual convenience updates in PyDOLFIN: TODO