Input DEM

Basic input DEMs configuration

A possible input DEM configuration would be the following:

"input_ref": {
  "path": "./Gironde.tif",
},
"input_sec": {
  "path": "./FinalWaveBathymetry_T30TXR_20200622T105631_D_MSL_invert.TIF",
}

Geoid reference

Demcompare requires the input DEMs to be geotiff files .tif.

The DEMs altitudes can rely on both ellipsoid and geoid references, being the ellipsoid the reference by default if not indicated otherwise. If DEMs altitudes are to rely on geoid, the configuration should be:

"input_sec" : {  "path":"./input_sec.tif"
                 "geoid_georef" : true,
              }

In this case, EGM96 geoid will be used by default.

Otherwise, the absolute path to a locally available geoid model can be given. The geoid local model should be either a GTX, NRCAN or NTv2 file.

For instance, if DEMs altitudes are to rely on a local .gtx available geoid model, the configuration should be:

"input_sec" : {  "path": "./input_sec.tif"
                 "geoid_georef": true,
                 "geoid_path": "path/to/egm08_25.gtx"
               }

ROI

To limit DEM comparison to a Region Of Interest (ROI) one can set a bouding box in terrain geometry or part of the DEM with image coordinates:

The geographical coordinates of the image defines as tuple with (left, bottom, right, top) coordinates. For instance, for a DSM whose Coordinate Reference System is EPSG:32630, a possible ROI would be (left=600255.0, bottom=4990745.0, right=709255.0, top=5099745.0).

"input_ref": {
  "path": "./Gironde.tif",
},
"input_sec": {
  "path": "./FinalWaveBathymetry_T30TXR_20200622T105631_D_MSL_invert.TIF",
  "roi": {
        "left": 40.5,
        "bottom": 38.0,
        "right": 44.0,
        "top": 41.0
      }
}

The image coordinates (x,y) of its top-left corner and its dimensions (w, h) in pixels defines as a python dictionary with x, y, w and h keys.

"input_ref": {
    "path": "./Gironde.tif",
  },
  "input_sec": {
    "path": "./FinalWaveBathymetry_T30TXR_20200622T105631_D_MSL_invert.TIF",
    "roi": {
          "x": 50,
          "y": 100,
          "w": 1000,
          "h": 500
        }
  }

Altimetric unit

Because it can happen that both DEMs would not have been produced with the same altimetric unit, the zunit parameter might be useful at times. It allows one to explicitly provide both DEMs unit, so that demcompare can convert z values adequately. The default zunit value is m.

"input_ref": {
    "path": "./Gironde.tif",
    "zunit": "cm",

  },
  "input_sec": {
    "path": "./FinalWaveBathymetry_T30TXR_20200622T105631_D_MSL_invert.TIF",
    "zunit": "m",
  }

Nodata

Demcompare will try to read the nodata value of each DEM from their metadata. However, another nodata value can be specified with the nodata parameter.

"input_ref": {
    "path": "./Gironde.tif",
    "nodata": -9999.0,

  },
  "input_sec": {
    "path": "./FinalWaveBathymetry_T30TXR_20200622T105631_D_MSL_invert.TIF",
    "nodata": -32768,
  }

Input DEMs configuration

This section details all input DEMs configuration parameters. Every parameter is a key for either the input_ref or the input_sec root configuration section.

Table 1 Input DEMs parameters
Name	Description	Type	Default value	Required
`'path'`	Path	string	`None`	Yes
`'roi'`	Processed Region Of Interest of the input Sec	Dict	`None`	No
`'geoid_georef'`	true if the georef of the input Ref	boolean	`false`	No
`'geoid_path'`	Geoid path of the input Ref	string	`None`	No
`'zunit'`	Z axes unit	string	`m`	No
`''nodata'`	No data value of the input Ref	int	`None`	No
`'classification_layers':{'name_map_path':}`	Path to the classification layer map	string	`None`	No

Note

'classification_layers':{'name_map_path':} is a parameter used for statistics purpose. See Statistics for more information.

Output configuration

Be aware that for a command line execution, one must set the output directory where data will be saved.

Name	Description	Type	Default value	Required
`'output_dir'`	Output directory path	string	`None`	Yes

Note

Demcompare accepts a single DEM as input. If it is the case, it must be defined as the input_ref.