B

FIGURE 11-23 Height points extracted with automatic image matching (top) and derived raster DEM (bottom) for the head of gully Salada 3, Province of Murcia, Spain. Derived from hot-air blimp aerial photography taken by IM, JBR, and M. Seeger, April 1998; photogrammetric processing by IM. (A) Uncorrected data showing numerous errors due to steep walls, overhangs, and vegetation (see arrows for examples). (B) Manually edited height points and derived DEM.

but also automatic DEM extraction—the image matching procedure may fail if the GSDs differ too much. Again, this may be avoided only by rejecting images that do not meet these requirements.

• Because SFAP images capture basically the same objects as medium to small-scale traditional aerials, but with much smaller GSD and from considerably lesser distance, some error-prone situations are actually amplified (see Fig. 3-16). The user should be aware that the number of erratic points in DEM extraction may increase with higher terrain complexity in terms of elevation variability and vegetation cover (Fig. 11-23). It is therefore highly advisable to provide for the possibility of visual 3D assessment of the results as well as terrain editing when choosing software for small-format aerial photogrammetry. Although encapsulated black-box workflows for direct DEM generation from stereopairs are fast and tempting, they tend to conceal the deficiencies in the raw dataset of extracted height points.

TABLE 11-1 Summary of imaging software usable for SFAP and supported image-processing tasks.

SFAP image processing

Simple ¡mage-viewing software

Camera software

Professional image-editing software

GIS software

Remote sensing software

Digital photogrammetry software

Import of camera-specific image formats

O

O

Camera-specific image enhancements *

O

Radiometric enhancements

0

resolution change

O

image rectification by GCPs

o

o

Image orthorectification

+

Combination with G!S vector data

o

o

Map layout

0

Image classification

o

+

Vector object extraction

o

+

+

+

Stereoscopic viewing

+

+

3D analysis 1 DEM extraction

Software examples

tfari View

All digital camera brands

Adobe Photoshop, Adobe Lightroom, NIH image, GIMP

ESRI ArcGIS,

GRASS, Quantum GIS, Intergraph Geo Media

ERDAS Imagine, IDRISI, ENVI, GRASS, PCI Geomatica

Leica Photogrammetry Suite, SocetSet, VirtuoZo, LISA, PhotoModeler

— Not available

Sometimes, indirectly or partly available

+ Usually available as an add-on module

Available

* White balance, optional lens-distortion correction, chromatic aberration, vignetting.

* White balance, optional lens-distortion correction, chromatic aberration, vignetting.

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