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SpatialConvexHull

Updated
globalmapper.SpatialConvexHull(GM_LayerHandle_t32 aLayer, GM_SpatialOps_Params_t aParams, GM_FeatureGrouping_t8 aGrouping, str aStr) → GM_Error_t32

The Convex Hull spatial transform creates a new layer with a polygon that encloses a set of points, lines, and/or areas. The polygon will be the smallest possible convex polygon that contains the features in the input layer; the shape of a convex hull is analogous to wrapping the features with a rubber band.

The aGrouping parameter controls how many polygons are created: with GM_GroupingNone, a polygon is created for each individual feature; with GM_GroupingPartition, one polygon will be created for each attribute group; and with GM_GroupingAll, all the features on the layer will be enclosed by one polygon.

For an even tighter fit hull, see SpatialConcaveHull.

Parameters:

  • aLayer (GM_LayerHandle_t32) – Input layer

  • aParams (GM_SpatialOps_Params_t) – Parameters

  • aGrouping (GM_FeatureGrouping_t8) – Grouping type

  • aStr (str) – The attribute list string; may be an empty string

Returns:

Error Code

Return type:

GM_Error_t32


BEFORE

AFTER
../_images/HullBefore.png ../_images/ConvexHull.png

Example

The following is an example of SpatialConvexHull.

import os
import globalmapper as gm

import_dir = "Z:/GM-20069/spatial_operations_sample_data/"
# Close all layers that may be open
layers_are_open = gm.GetLoadedLayerList()
if layers_are_open:
    arr_ptr, arr_size = layers_are_open
    initial_layers = gm.GM_LayerHandle_array_frompointer(arr_ptr)
    for i in range(arr_size):
        gm.CloseLayer(initial_layers[i])

err_LoadLayerList, array_pointer, array_size_param = gm.LoadLayerList(
    os.path.join(import_dir, "points.shp"),
    gm.GM_LoadFlags_HideAllPrompts,
)

# Get handle for the loaded layers
arr_ptr, arr_size = gm.GetLoadedLayerList()
layers_array = gm.GM_LayerHandle_array_frompointer(arr_ptr)
layers_list = gm.carray_to_list(layers_array, arr_size)

### START SAMPLE
spatial_params = gm.GM_SpatialOps_Params_t()
spatial_params.mResultLayerName = "ConvexHull_Result"
err_SpatialConvexHull = gm.SpatialConvexHull(
    layers_list[0], spatial_params, gm.GM_GroupingAll, ""
)

### END SAMPLE

assert (
    gm.GM_Error_None == err_LoadLayerList
), f"LoadLayerList: Expected {gm.GM_Error_None}, got {err_LoadLayerList}"
assert (
    gm.GM_Error_None == err_SpatialConvexHull
), f"SpatialConvexHull: Expected {gm.GM_Error_None}, got {err_SpatialConvexHull}"

assert os.path.isdir(import_dir), f"Import directory doesn't exist: {import_dir}"
assert os.path.exists(
    os.path.join(import_dir, "points.shp")
), "Sample data doesn't exist"