more parameter settings are required for algorithms endpoints

[JinIgarashi]

Currently titiler's algorithms api returns parameters with default, title and type only. It would be nice if the api can return more settings for parameters such as maxValue, minValue. If these settings are available, it is easier to make slider UI for parameters.

In addition, in default example of algorithms, there is not string parameters. it would be nice if option values can be included in parameter settings (like for making selecting box) if it is string type.

There additional parameter settings can be useful if frontend side want to build a UI dynamically.

[vincentsarago]

@JinIgarashi I'm not quite sure to fully understand, to you have an example?

titiler/src/titiler/core/titiler/core/algorithm/dem.py

Lines 12 to 23 in 70c18b3

	class HillShade(BaseAlgorithm):
	"""Hillshade."""
	# parameters
	azimuth: int = 90
	angle_altitude: float = 90.0
	buffer: int = 3
	# metadata
	input_nbands: int = 1
	output_nbands: int = 1
	output_dtype: str = "uint8"

curl https://titiler.xyz/algorithms/hillshade | jq
{
  "inputs": {
    "nbands": 1
  },
  "outputs": {
    "nbands": 1,
    "dtype": "uint8",
    "min": null,
    "max": null
  },
  "parameters": {
    "azimuth": {
      "default": 90,
      "title": "Azimuth",
      "type": "integer"
    },
    "angle_altitude": {
      "default": 90.0,
      "title": "Angle Altitude",
      "type": "number"
    },
    "buffer": {
      "default": 3,
      "title": "Buffer",
      "type": "integer"
    }
  }
}

everything comes from https://github.com/developmentseed/titiler/blob/main/src/titiler/core/titiler/core/factory.py#L1654C30-L1654C64 (pydantic method)

HillShade.model_json_schema()["properties"]

{'input_nbands': {'default': 1, 'title': 'Input Nbands', 'type': 'integer'},
 'output_nbands': {'default': 1, 'title': 'Output Nbands', 'type': 'integer'},
 'output_dtype': {'default': 'uint8',
  'title': 'Output Dtype',
  'type': 'string'},
 'output_min': {'anyOf': [{'items': {}, 'type': 'array'}, {'type': 'null'}],
  'default': None,
  'title': 'Output Min'},
 'output_max': {'anyOf': [{'items': {}, 'type': 'array'}, {'type': 'null'}],
  'default': None,
  'title': 'Output Max'},
 'azimuth': {'default': 90, 'title': 'Azimuth', 'type': 'integer'},
 'angle_altitude': {'default': 90.0,
  'title': 'Angle Altitude',
  'type': 'number'},
 'buffer': {'default': 3, 'title': 'Buffer', 'type': 'integer'}}

in your custom algorithm, if you see min/max value for a properties using Pydantic Field you should get the info in the endpoint

from titiler.core.algorithm.base import BaseAlgorithm
from pydantic import Field
from rio_tiler.models import ImageData

class Something(BaseAlgorithm):

    # parameters
    yo: int = Field(90, ge=0, lt=100)

    def __call__(self, img: ImageData) -> ImageData:
        return img

Something.model_json_schema()["properties"]

{'input_nbands': {'anyOf': [{'type': 'integer'}, {'type': 'null'}],
  'default': None,
  'title': 'Input Nbands'},
 'output_nbands': {'anyOf': [{'type': 'integer'}, {'type': 'null'}],
  'default': None,
  'title': 'Output Nbands'},
 'output_dtype': {'anyOf': [{'type': 'string'}, {'type': 'null'}],
  'default': None,
  'title': 'Output Dtype'},
 'output_min': {'anyOf': [{'items': {}, 'type': 'array'}, {'type': 'null'}],
  'default': None,
  'title': 'Output Min'},
 'output_max': {'anyOf': [{'items': {}, 'type': 'array'}, {'type': 'null'}],
  'default': None,
  'title': 'Output Max'},
 'yo': {'default': 90,
  'exclusiveMaximum': 100,
  'minimum': 0,
  'title': 'Yo',
  'type': 'integer'}}

In addition, in default example of algorithms, there is not string parameters. it would be nice if option values can be included in parameter settings (like for making selecting box) if it is string type.

Again I'm not sure to get this, but have to use JSON encoded parameters for algorithm because we need named parameters and we also need type checking from pydantic

[JinIgarashi]

currently, for example, hillshade algorithms returns

  "parameters": {
    "azimuth": {
      "default": 90,
      "title": "Azimuth",
      "type": "integer"
    },
    "angle_altitude": {
      "default": 90.0,
      "title": "Angle Altitude",
      "type": "number"
    },
    "buffer": {
      "default": 3,
      "title": "Buffer",
      "type": "integer"
    }
  }

but for users, we are unable to know what range of values are expected for these parameters. They only have default and type. It would be nice if titiler also returns min and max.

for instance, about azimuth parameter, we can know the value should be between 0 and 360 (as human being reading), but it is not easy to decide the range of values by programming code to create a UI dynamic. I think now my point is clear to you?

[vincentsarago]

Ok oK 👍

so it's not a general problem, but more a problem with how the Hillshade algorithm class is currently written. Please feel free to open a PR to add the min / max values for the parameters 🙏

[JinIgarashi]

@vincentsarago I created a PR #783 for this