# Preparing an orthophoto as a base map

> Source: https://topodrone.com/knowledge/topodrone-aquamapper-user-manual/preparing-an-orthophoto-as-a-base-map/
> Section: TOPODRONE AQUAMAPPER User Manual
> Updated: 2026-10-02

To ensure safe bathymetric survey within a water body, before working with TOPODRONE AQUAMAPPER you must [perform high-precision aerial photography](https://knowledge.topodrone.com/shelves/photogrammetry) (hereinafter aerial survey) of the water body with an absolute horizontal accuracy of 3-5 cm. The result of the high-precision aerial survey is a georeferenced orthophoto of a quality that allows the shoreline to be determined precisely. Orthophoto output format - **\*.tiff**. Coordinate system - **WGS84**.

Use the orthophoto to study the water body for rocks, nets and other mechanical obstacles that could damage TOPODRONE AQUAMAPPER during work. Areas with mechanical obstacles can then be marked as no-fly zones when planning routes, to avoid collisions with TOPODRONE AQUAMAPPER during the UAS flight.

> **Warning:** If the water body to be surveyed is connected to the ocean and affected by tides, determine the shoreline at low tide, since the bottom relief of the drained surface can be determined with high-precision aerial photography and photogrammetric post-processing.

> **Note:** For convenient route planning later, it is recommended to draw the water body boundaries in any GIS software and then generate the TOPODRONE AQUAMAPPER survey boundaries with an offset of 2-3 meters towards greater depth. Output file format - \*.kml