C++-Style Arrays for GM Types in Python

Many functions in Global Mapper require array data structures for inputting data, rather than the typical Python list, to help keep the API for GM Python and the C++/C# SDK as similar as possible. To make use of arrays in Python, the Global Mapper module provides various array types that can be initialized to the desired size:

attribute_array = gm.GM_AttrValue_array(10)

Like in C++, these arrays are stored linearly in memory and have a fixed size, which is specified when they are created. For example, in the line above, a value of ‘10’ means that the array will be big enough to contain 10 GM_AttrValue_t objects.

After initializing the array, you can populate it in the same manner as with a standard python list, using the [] operator:

import globalmapper as gm

area_feature_list = [  ... ]  # your list of GM_AreaFeature_t objects
num_features = len(area_feature_list)
area_feature_array = gm.GM_AreaFeature_array(num_features)

for i in range(num_features):
    area_feature_array[i] = area_feature_list[i]

The above example demonstrates converting a Python list of area feature objects into a GM array, using the array type GM_AreaFeature_array. The size of the array is declared in the constructor; in this case, it uses the number of items in the list to allocate an array of the same size. Once the array is created, you can use the [ ] operator to index and modify the array in the same manner as a list.

Here is a fully functional example of the code shown above that can be used to further experimentation. This script can be run as is and will output some details about the objects loaded in the array.

# Creating 3 area feature objects and assigning a point count
feature1 = gm.GM_AreaFeature_t()
feature1.mNumPoints = 27
feature2 = gm.GM_AreaFeature_t()
feature2.mNumPoints = 36
feature3 = gm.GM_AreaFeature_t()
feature3.mNumPoints = 51

# Your list of GM_AreaFeature_t objects
area_feature_list = [feature1, feature2, feature3]
num_features = len(area_feature_list)
area_feature_array = gm.GM_AreaFeature_array(num_features)

# Convert area feature list into C++-style array
for i in range(num_features):
    area_feature_array[i] = area_feature_list[i]

print("Feauture1 data: " + str(area_feature_array[0].mNumPoints))
print("Feauture2 data: " + str(area_feature_array[1].mNumPoints))
print("Feauture3 data: " + str(area_feature_array[2].mNumPoints))

Sometimes a function may return a pointer to an array, rather than an array itself. In those cases, you can use a special function in the form x_array_frompointer, substituting “x” for the appropriate object type; for example, the function GM_LayerHandle_array_from_pointer can be used on the pointer returned by GetLoadedLayerList to get an indexable array.

For more detail and examples about pointers in Global Mapper, see: Converting a Pointer to an Array or List.

Below are all the supported array types in Global Mapper Python scripting:

• COLORREF_array

• double_array

• float_array

• GM_AreaFeature_array

• GM_AttrValue_array

• GM_CustomShader_array

• GM_ElevColor_array

• GM_FoundFeature_array

• GM_GroundControlPoint_array

• GM_LayerHandle_array

• GM_LidarAttrInfo_array

• GM_LidarPoint_array

• GM_LidarReturnInfo_array

• GM_OnlineSourceInfo_array

• GM_PaletteEntry_array

• GM_Point_t_array

• GM_ValName_array

• uint8_array

• uint32_array