Читать книгу Imagery and GIS - Kass Green - Страница 70

Ultimately, the project budget will limit the maximum expenditure on imagery and budgets often force trade-offs in project requirements. In the United States, multiple spatial and temporal resolutions are abundant and accessible at no charge (e.g., NAIP, Landsat, or imagery acquisitions funded by local agencies). More costly new or higher-spatial-resolution imagery can be acquired from commercial airborne and satellite operators. Outside of the United States, moderate-spatial-resolution imagery (e.g., Landsat and Sentinel) is freely available, but high-resolution imagery usually is either restricted by government programs or is sold by commercial companies under a license agreement.