# Automated Tree Detection Using Image Processing and Multisource Data
## 3 Background
### Spatial Maps and Geoinformation Data  
The first two data types, namely numerical terrain and land-cover models, are files with a.asc extension. These data contain information about the area, including the coordinates (Easting and Northing), the size of the area, and the height above sea level. Numerical land-cover models describe the height above sea level of all objects, such as trees and buildings, whereas numerical terrain models represent the height of the land itself. Data of this type are always presented with a certain level of accuracy, most commonly to the nearest meter. Thus, each map can be divided into numerous small segments, each with an area of 1 square meter. The format of.asc files is detailed in Table 1. These files encapsulate both numerical terrain and land-cover models. The first two parameters denote the division of the grid into segments along the longitude and latitude axes. Subsequent entries specify the coordinates of the area's initial point, followed by the segment size, which dictates the measurement interval. In the example depicted, the grid is segmented into 1 m by 1 m squares. The data that follow represent elevation levels above sea level. Numerical terrain model maps detail the land's elevation, whereas numerical land-cover models illustrate the height of all surface objects, including buildings and trees, above sea level. By comparing the values across these two models for specific coordinates, one can determine the height of various objects. Color Infrared (CIR) remote sensing data, represented as normalized difference vegetation index (NDVI) images, offer insights into vegetation health through the contrast between the visible and near-infrared reflectance of plants. This method serves as a powerful, non-invasive tool for assessing vegetation. The data are stored in.tif format (TIFF), with each image corresponding to a specific map segment and including coordinate information. An example of a.tif file is illustrated in Figure 1, which differentiates between vegetation and urban structures using color intensity. For instance, a vivid red color signifies dense vegetation, while blue, gray, and yellow hues indicate areas with minimal or no vegetation. GeoTIFF data encompass an urban area segmented into 562 zones, each measuring 500 by 800 m. This format serves as an open metadata standard that augments.tif files with georeferencing and geocoding data. Included in this added information are geographic coordinates, datum parameters, and mapping details, among others, which are instrumental in analyses such as vegetation index studies. The final data format discussed is the world file for.tif files, which augments.tif files with additional information. Each corresponding.tfw file matches the coverage area of its.tif counterpart. Furthermore,.tfw files, in ASCII text format, provide rotation details and geographic coordinates for TIFF images. An example of a file with a.tfw extension is illustrated in Table 2. This file complements the graphic NDVI files by containing additional metadata not present in the image itself, which indicate vegetation levels. In the example provided, the.tfw file comprises a series of lines that specify the X and Y pixel sizes, rotation information, and world coordinates \begin{table}
\begin{tabular}{c c} \hline \hline
**Numerical Terrain Model** & **Numerical Land-Cover Model** \\ \hline number of columns & number of columns \\ number of rows & number of rows \\ x coordinate center & x coordinate center \\ y coordinate center & y coordinate center \\ segment size [in square meters] & segment size [in square meters] \\ \hline
**Example data** & **Example data** \\ \hline
299.95 299.90 299.86 \(\ldots\) & 306.22 305.42 304.39 \(\ldots\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Numerical terrain and numerical land-cover models: Description of attributes and example data. Figure 1: Example of a Color Infrared (CIR) image representing the normalized difference vegetation index (NDVI). for the upper-left corner of the image.