CEIT

Python Package for EIT(Electric Impedance Tomography)-like method on detecting capacitance Density Distribution.

Table of Contents

• CEIT
  • Table of Contents
  • Overview
  • Installment
  • Configure the calculation
  • Quick Start
  • Read Mesh Class
    • 1. Initialize a new mesh
    • 2. Read from generated mesh cache
  • Forward Simulator
  • Jacobian Constructor
  • Realtime Solver
  • How to implement your own forward model?
  • Cite our work

Overview

This python package is designed for solving the tomographic problem concerned with detecting proximity map by a planar conductive sensor.

It can also be used on other "weird" types of EIT-like problem(different differential equation compared to traditional EIT), this package is now focusing on Gauss-Newton solver. If you are looking into impedance problem specifically, then maybe you want to check out this package.

For more information, please check my paper.

The EFEM class is written only for this problem, other modules can be reused in any other EIT application.

CEIT provides the ability to generate solver for realtime reconstruction. Given the meshes and electrode positions, CEIT can generate Inverse model for any planar sensor design.

KIND REMINDER: be sure to config the .gitignore file, the .csv files generated are pretty large...

Installment

Install through pip or download the code.

pip install CEIT

If you download this code, see requirements.txt, one thing to mention is that to accelerate the calculation process, you can use GPU acceleration. To enable this you have to do the following steps.

1. Set the "device" option in config.json to "gpu"
2. Cancel the comment inside function calculate_FEM_equation() at the end of file ./MyEIT/efem.py.
3. cancel the line of import cupy as cp in ./MyEIT/efem.py.
4. Install cupy package according to your CUDA version, e.g. python -m pip install cupy-cuda101 , check the installation guide here.

Currently this package only work on 2D meshes.

Configure the calculation

You should configure the config.json file before using this package.

Please put the config.json file in the same folder as \MyEIT.

A .fem file is needed for initializing the whole process. You can get one by using CAD software.

Also, you have to decide your electrode center positions, and your radius of the electrode. Inside this package, the electrode is square shaped for which the radius means half width of the square. Be sure to set all the fields.

For Examples see config.json file.

Parameter Name	Type	Description
"signal_frequency"	Number	Frequency of your input signal unit: Hz
"resistance"	Number	The resistance of the coductive sheet unit: Ω/sq
"mesh_filename"	String	File name for your mesh file
"folder_name"	String	Specify the folder you wish to put your mesh file and all the cache files.
"optimize_node_num"	Boolean	Whether shuffle node number at initializing mesh
"shuffle_element"	Boolean	Whether shuffle elemets at initializing mesh
"electrode_centers"	Array	Center of electrodes on perimeter THE UNIT IS mm
"electrode_radius"	Number	In this package electrodes are treated as square shaped, this parameter is half of its side length.
"variable_change_for_JAC"	Number	variable change on every single element when calculating the Jacobian matrix.
"detection_bound"	Number	Specify the detection boundary size please keep its unit identical to the "unit" property
"calc_from"	Number	Set starting electrode for Jacobian calculation, for multiple instances compute usage.
"calc_end"	Number	Set ending electrode for Jacobian calculation, for multiple instances compute usage.
"regularization_coeff"	Number	This parameter is used in regularization equation of reconstruction, you will have to optimize it.
"device"	String	Calculation device, only "cpu" or "gpu" is accepted, if you choose "cpu" please follow the instructions in the previous paragraph.
"sensor_param_unit"	String	Unit for the input sensor parameters above. Only "mm" or "SI" is accepted, they will all be transferred into SI unit.
"mesh_unit"	String	the length unit of your mesh file there are 4 options mm cm m inch.
"reconstruction_mode"	String	DEPRECATED ITEM keep this to "n"
"overall_origin_variable"	Number	DEPRECATED ITEM keep this to 0

Quick Start

There are some samples in the folder.

• Example_01 Initilize Mesh
• Example_02 Forward Calculation
• Example_03 Generate jacobian matrix
• Example_04 Realtime solver

Read Mesh Class

All the mesh initializer is put in MyEIT.ReadMesh.

Now the reader only work with .fem files generated by Altair HyperMesh and the standard calculation unit of length inside this package is METER.

1. Initialize a new mesh

First you should finish configuring your config.json file according to the previous paragraph.

Your mesh length unit should be corresponding to "mesh_unit" option inside config.json.

The initializer can accept 4 kinds of units mm | cm | m | inch.

Then on the first time running of a new mesh, call init_mesh() function to initialize mesh.

When initializing, the class will automatically clear out duplicated mesh and you can decide whether it should shuffle the mesh number or not.

After initializing, in the folder you specified before, the method would generate a Mesh_Cache_Node.csv file and a Mesh_Cache_Element.csv file.

from CEIT.readmesh import init_mesh

init_mesh(draw=True)

2. Read from generated mesh cache

After initializing the mesh, you can quickly read from the cache file.

All the config value inside the json file which is related to length is in "sensor_param_unit" only "mm" and "SI" is supported

Class read_mesh_from_csv provides function to read mesh from csv file. The default calculation unit inside CEIT is SI units, if your mesh is in mm unit, please set in config.json file.

You need to call return_mesh() method to get the mesh object and electrode information.

from CEIT.readmesh import read_mesh_from_csv

read_mesh = read_mesh_from_csv()
mesh_obj,_,_,_ = read_mesh.return_mesh()

Forward Simulator

The forward calculator is used Finite Element Method to calculate potential distribution on the surface.

First instantiate the class after reading the mesh file.

from CEIT.EFEM import EFEM

fwd_model = EFEM()

The initializer will automatically prepare the object for calculation, now you have a fully functioning forward solver.

There are several functions provided by this object you can call to change variable value and do calculation.

function Name	Description
EFEM.calculation(electrode_input)	Forward calculation on given input electrode selection You have to call this to do the calculation
EFEM.plot_potential_map(ax)	Plot the current forward result, default is 0 before calling calculation()
EFEM.plot_current_variable(ax)	Plot the given input condition
EFEM.change_variable_elementwise(element_list, variable_list)	Change variable density on selected elements
EFEM.change_variable_geometry(center, radius, value, shape)	Assign variable density on elements inside a certain geometry (square or circle) to the given value
EFEM.change_add_variable_geometry(center, radius, value, shape)	Add the given variable density on elements inside a certain geometry
EFEM.change_conductivity(element_list, resistance_list)	Change conductivity on certain elements
EFEM.reset_variable(overall_variable)	Set variable density on all elements to overall_variable

Jacobian Constructor

The EJAC class provides the function of doing jacobian calculation.

First instantiate the class, this class doesn't require creating the EFEM class, it will initialize it internally. However, you have to get the mesh and pass it into the initializer

from CEIT.EJAC import EJAC

jac_calc = EJAC()
jac_calc.JAC_calculation()

If you had set the value "is_first_JAC_calculation" inside config.json file to true, then, if you call method EJAC.JAC_calculation() , it will start calculating the jacobianmatrix starting from electrode "calc_from" to "calc_end". This allows you to calculate the jacobian matrix on different machines and then combine them together. After one iteration (an electrode input condition), the function saves JAC matrix to cache file JAC_cache.npy.

If the calculation is completed make sure you change the "is_first_JAC_calculation" property to false, so it won't calculate unexpectedly.

This calculation takes a lot of time so please make sure everything's right before starting.

This class also provide some methods for you to reconstruct actual EIT data.

Function Name	Description
EJAC.JAC_calculation()	Calculate and return JAC Matrix, Auto Save to File on every iteration
EJAC.eit_solve(self, detect_potential, lmbda)	Solve inverse problems base on the initial amplitude output (with no object above) generated by simulation This is for simulation
EJAC.eit_solve_4electrodes()	Solving 4 electrode condition. There are also functions for 8 electrodes
EJAC.eit_solve_delta_V()	Reconstruct based on the given amplitude change This is for testing, use solver for realtime calculation
EJAC.save_inv_matrix(lmbda)	set up inverse matrix for realtime solver with regularization parameter lmbda
EJAC.show_JAC()	Visualize jacobian matrix with color map
To do more with the package, Please read the comment inside ejac.py.

Realtime Solver

The Solver class provides the function of realtime reconstructing data fed in to the Solver.solve() function. Solver class only has one method Solver.solve().

An example

from CEIT.Solver import Solver
import numpy as np

solver = Solver()
delta_v = np.random.rand(240)
solver.solve(delta_v)

If you generated another Jacobian matrix, you can call the function reinitialize_solver() contained in the MyEIT.solver module to refresh your inv_mat.npy file.

from CEIT.Solver import reinitialize_solver

reinitialize_solver()

How to implement your own forward model?

For typical 2D EIT problems, this package can handle all the requirements from interpreting .fem mesh file, assigning electrode position, generating JAC matrix to solving the problem with ease of use.

With different differential equation, the FEM model is almost the same, but the core simulation algorithm has to be edited.

Check the FEMBasic class and EFEM class, FEMBasic class is an abstract class whose my_solver function is an abstract method. Override this method to get your own forward simulator.

Cite our work

This package is used in our paper presented on IECON 2020 conference, if you find this package helpful, please cite our work.

@INPROCEEDINGS{
  9254590,
  author={Z. {Li} and S. {Yoshimoto} and A. {Yamamoto}},
  booktitle={IECON 2020 The 46th Annual Conference of the IEEE Industrial Electronics Society}, 
  title={Tomographic Approach for Proximity Imaging using Conductive Sheet}, 
  year={2020},
  volume={},
  number={},
  pages={748-753},
  keywords={Tomography;proximity imaging;haptics;robot-skin},
  doi={10.1109/IECON43393.2020.9254590},
  ISSN={2577-1647},
  month={Oct},
}