v.to.db: add JSON support

[kritibirda26]

Add JSON output support to v.to.db module. The output looks like as follows:

{
    "totals": {
        "area": 2219442027.2203522
    },
    "records": [
        {
            "category": 1,
            "area": 24375323.127803534
        },
        {
            "category": 2,
            "area": 2938964.3204806102
        },
        {
            "category": 3,
            "area": 50536154.294107705
        }
    ],
...
}

[kritibirda26]

@cwhite911 Hi! Can you please review this PR? I would like to use the JSON format added here in the v.report module's JSON implementation to keep the implementation simple.

[cwhite911]

@cwhite911 Hi! Can you please review this PR? I would like to use the JSON format added here in the v.report module's JSON implementation to keep the implementation simple.

@kritibirda26 the schema looks good to me, however I'm debating if we should add the measurement unit to the root object.

[echoix]

If it's documented for now, it won't be breaking to add it at a later time if needed. So if you can't decide after thinking about it for a while, there's a way to keep the PR going.

[cwhite911]

@kritibirda26 This is looking good. Please add test for all of the possible output schemas and update the docs to make it clear that output format only works when the -p flag is set.

[kritibirda26]

@cwhite911 can you please take another look at this PR?

[cwhite911]

@kritibirda26 Please add additional unit tests to capture the all of the response data types (point, line, polygon, 3d vectors, mixed with the options: cat, area, compact, fd, perimeter, length, count, coor, start, end, sides, query, slope, sinuous, azimuth, bbox.

Let's also add the measurement unit to the root json object.

[kritibirda26]

@cwhite911 Should there be at least one test covering each type and each option? asking because it doesn't seem possible to provide multiple options or types to v.to.db at once.

[cwhite911]

@cwhite911 Should there be at least one test covering each type and each option? asking because it doesn't seem possible to provide multiple options or types to v.to.db at once.

Yes, we should add a test to make sure each key value pair is correctly generated for the option.

[kritibirda26]

@cwhite911 I have added more tests and measurement units to the root of the object. Can you please suggest which maps/commands to use to test query, azimuth, sinuousity and slope?

[echoix]

Also make sure to avoid the uninitialized warning like the other module.

[cwhite911]

I'm not sure what you mean here. Will you remind me of the other module?

[echoix]

ff98e42,
Follow the PR, the comment, and if you have access to coverity, the new detection after the PR #4201 was merged.

[cwhite911]

The azimuth is calculated from a line feature. I suggest using the majorroads layer for the test.

Azimuth

v.to.db -p map=roadsmajor@PERMANENT option=azimuth units=radians format=json

v.to.db -p map=roadsmajor@PERMANENT option=azimuth units=degrees format=json

Sinuous

v.to.db -p map=roadsmajor@PERMANENT option=sinuous format=json

Slope

To test slope I don't think we have a layer in the test dataset the is line feature with z coordinates.

For the test you could create one using v.to.3d and then testing that with

v.to.db -p map=roadsmajor3d option=slope units=degrees format=json

[kritibirda26]

@cwhite911, Hi! I have updated the PR with tests for azimuth and sinuous. For slope, I tried to create a 3d map but failed. I also followed other examples of creating a 3d dataset from 2d (from the tests of other modules) but the slope always comes to be 0 in both plain and json mode.