GAMMA product cannot be geocoded correctly

[wwe-gif]

Hi, everyone! when I use Mintpy to process the result of GAMMA product, it looks like correct in the whole process. But, when I look at the geocoded product, value is zero for all, can anyone explain why is it? please note that before geocoding, value is correct.

Here is my screenshot:

Before geocoding:

After geocoding:

and my configure file :

sbas.txt

note that full script has no error

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[yunjunz]

Please provide more information for diagnosis:

1. plot your velocity files before and after geocoding
2. plot your geometryRadar.h5 and geometryGeo.h5 file
3. and maybe share the above data files directly for error reproduction, either publically here or privately to me (yunjunz@outlook.com).

[codeautopilot[bot]]

Potential Solution

The bug causing the GAMMA product to have zero values after geocoding likely stems from issues with the lookup table or the interpolation method used during the geocoding process. To solve this, we should ensure that the lookup table is correctly aligned with the input data and experiment with different interpolation methods to find the most suitable one. Additionally, we should verify that the fill value is appropriate for the data type and does not inadvertently set values to zero.

What is Causing This Bug?

The bug is likely caused by one or more of the following issues:

1. Incorrect Lookup Table: If the lookup table used for geocoding is not properly aligned with the input data's coordinate system, it can result in incorrect geocoding, leading to zero values in the output.

2. Interpolation Method: The default interpolation method (nearest) might not be suitable for the data, resulting in unexpected output. If the interpolation method does not handle the data correctly, it could lead to zero values.

3. Fill Value Misconfiguration: The fill value for extrapolation is set to 0 for certain file types (e.g., .int or .unw). If this fill value is applied incorrectly, it could cause the output to have zero values.

4. Coordinate System Misidentification: If the script incorrectly identifies the coordinate system of the input files, it might skip necessary processing steps, leading to incorrect outputs.

Code

To address these issues, we can make the following changes:

1. Verify and Correct the Lookup Table: Ensure that the lookup table is correctly aligned with the input data's coordinate system.

2. Experiment with Interpolation Methods: Modify the geocoding script to try different interpolation methods and see if the issue persists.

# Example modification in geocode.py
interpolation_method = 'linear'  # Change from 'nearest' to 'linear'

3. Review and Adjust Fill Value: Confirm that the fill value is appropriate for the data type and does not inadvertently set values to zero.

# Example modification in geocode.py
fill_value = np.nan  # Ensure fill value is set to NaN for extrapolation

4. Ensure Correct Coordinate System Identification: Double-check that the input files are correctly identified as radar or geo-coordinates.

How to Replicate the Bug

To replicate the bug, follow these steps:

1. Use MintPy to process a GAMMA product with the current configuration.
2. Ensure that the lookup table and interpolation method are set to their default values.
3. Run the geocoding process.
4. Observe the output to see if the geocoded product has zero values.

By following these steps, you should be able to replicate the issue and test the proposed solution to verify its effectiveness.

Click here to create a Pull Request with the proposed solution

Files used for this task:

Changes on docs/FAQs.md

The `docs/FAQs.md` file provides general information about preparing input data for MintPy, including supported formats and metadata requirements. However, it does not contain specific FAQs related to geocoding issues with GAMMA products. To address the user's issue, it would be beneficial to add an FAQ entry that specifically addresses common geocoding problems with GAMMA products, such as ensuring that the lookup table files (e.g., `sim_*.UTM_TO_RDC`) are correctly used and that all input files have consistent spatial extents and resolutions. Additionally, guidance on verifying the integrity of the geocoding process and troubleshooting zero-value outputs could be helpful. In summary, this file does not currently address the specific issue reported by the user, and adding relevant information could improve user support for similar problems.

Changes on src/mintpy/cli/geocode.py

## Analysis of `src/mintpy/cli/geocode.py` The `geocode.py` script is responsible for resampling radar-coded files into geo-coordinates or vice versa. The script uses command-line arguments to specify input files, geocoding parameters, and output options. Here's a breakdown of the key components and potential issues that could lead to the bug described: ### Key Components 1. **Argument Parsing**: The script uses `argparse` to handle command-line arguments. It includes options for specifying input files, lookup tables, bounding boxes, interpolation methods, and more. 2. **Lookup Table**: The script requires a lookup table for geocoding. If the lookup table is not provided or found, the script raises an error. 3. **Coordinate Checks**: The script checks whether the input files are already geocoded or in radar coordinates and exits if the operation is not applicable. 4. **Interpolation**: The script supports different interpolation methods (`nearest`, `linear`) and uses `pyresample` or `scipy` for processing. 5. **Error Handling**: The script includes several checks and error messages for invalid combinations of options, such as using `--lalo-step` with `--geo2radar`. ### Potential Issues 1. **Lookup Table**: If the lookup table is incorrect or not properly aligned with the input data, it could result in incorrect geocoding, potentially leading to zero values in the output. 2. **Interpolation Method**: The default interpolation method is `nearest`. If this method is not suitable for the data, it might result in unexpected output. The user might need to experiment with different methods. 3. **Fill Value**: The default fill value for extrapolation is `NaN`, but it changes to `0` for `.int` or `.unw` files. If the input data is of these types and the fill value is applied incorrectly, it could lead to zero values. 4. **Coordinate Checks**: If the script incorrectly identifies the coordinate system of the input files, it might skip necessary processing steps, leading to incorrect outputs. 5. **Template File**: If a template file is used, it might override command-line options. Ensure that the template file settings are correct and consistent with the desired output. ### Recommendations - **Verify Lookup Table**: Ensure that the lookup table is correct and matches the input data's coordinate system. - **Check Interpolation Method**: Experiment with different interpolation methods to see if the issue persists. - **Review Fill Value**: Confirm that the fill value is appropriate for the data type and does not inadvertently set values to zero. - **Coordinate System**: Double-check that the input files are correctly identified as radar or geo-coordinates. - **Template Settings**: If using a template file, review its settings to ensure they align with the intended geocoding process. These steps should help identify and resolve the issue of zero values in the geocoded output. If the problem persists, further investigation into the specific data and configuration used may be necessary.

Changes on docs/api/coord.md

# Analysis Report ## Overview The file `docs/api/coord.md` provides documentation on the coordinate systems used in MintPy, specifically focusing on radar and geo coordinates. It explains the parameters involved in defining geo coordinates, such as `X_FIRST`, `Y_FIRST`, `X_STEP`, `Y_STEP`, `X_UNIT`, and `Y_UNIT`. ## Relevance to the Bug The issue reported involves incorrect geocoding of GAMMA products, resulting in zero values after the geocoding process. This documentation file is intended to describe the geocoding process and any potential pitfalls, which could help users understand and troubleshoot issues related to coordinate transformations. ## Findings - The documentation provides a basic explanation of the geo coordinate system and the parameters used to define it. - It includes an example of how these parameters are set for a specific dataset. - There is no mention of common errors or pitfalls that users might encounter during the geocoding process, which could be relevant to the issue reported. ## Potential Causes of the Bug While this documentation does not directly address the bug, the lack of detailed information on potential pitfalls or common errors in the geocoding process might leave users without guidance on troubleshooting issues like the one reported. ## Recommendations - **Enhance Documentation**: Update the documentation to include a section on common errors and troubleshooting tips related to geocoding. This could help users identify and resolve issues more effectively. - **Cross-reference with Other Documentation**: Ensure that this document is consistent with other related documentation, such as FAQs or user guides, to provide comprehensive guidance on geocoding. This file alone does not provide enough information to identify the root cause of the bug, but improving the documentation could aid users in diagnosing similar issues in the future.

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[wwe-gif]

Sorry,I have solved this later. this is due to wrong input files. GAMMA products use isometric projection(EQA) in default. but, in Mintpy UTM has been suggested in utils/prep_gamma.py  file. so i change it into UTM. The point of problem is unit. After i change it into UTM, unit is m. however, the program need degree, so, i find that is wrong. Then, I input the original EQA files, it works successfully. I think it may need to change the UTM info in prep_gamma.py. many may be mistaken by it.

Thanks! 

------------------ 原始邮件 ------------------ 发件人: "insarlab/MintPy" @.>; 发送时间: 2024年11月11日(星期一) 凌晨0:31 @.>; @.**@.>; 主题: Re: [insarlab/MintPy] GAMMA product cannot be geocoded correctly (Issue #1270)

Please provide more information for diagnosis:

plot your velocity files before and after geocoding

plot your geometryRadar.h5 and geometryGeo.h5 file

and maybe share the above data files directly for error reproduction, either publically here or privately to me @.***).

— Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you authored the thread.Message ID: @.***>

[yunjunz]

I am glad to hear you located the problem. Gamma is very flexible in terms of format, which is a good and bad thing at the same time. From my understanding, we need two examples: one in UTM, and one in EQA coordinates. Each of them needs an example dataset and a detailed data structure documentation, to avoid future confusion. I am not a Gamma user. You are more than welcome to contribute to this.