Manual mapping of a synthetic landscape to assess operator effectiveness

Tuesday, September 23, 2014 at 15:31:22

Hillier, J.K., Smith, M.J., Barr, L., Boston, C., Clark, C.D., Ely, R., Fankl, A., Greenwood, S., Gosselin, L., Hattesrand, C., Hogan, K., Hughes, A., Livingstone, S.J., Lovell, H., McHenry, M., Munoz, Y., Pelicier13, X., Pellitero, R., Robb, C., Robertson, S., Ruther, D., Spagnolo, M., Standell, M., Stokes, C., Storrar, R., Tate, N., Wooldridge, K. (2015)
Journal of Maps

Mapped topographic features are important for understanding processes that sculpt the Earth’s surface. This paper presents maps that are the primary product of an exercise that brought together 27 researchers with an interest in landform mapping where the efficacy and causes of variation in mapping were tested using novel synthetic DEMs containing drumlins. The variation between interpreters (e.g., mapping philosophy, experience) and across the study region (e.g., woodland prevalence) opens these factors up to assessment. A priori known answers in the synthetics increase the number and strength of conclusions that may be drawn with respect to a traditional comparative study. Initial results suggest that overall detection rates are relatively low (34-40%), but reliability of mapping is higher (72-86%). The maps form a reference dataset.

OPEN ACCESS EPRINT: Multiresolution segmentation to automatically delimit landforms in DEMs: tests using synthetic drumlins

Tuesday, September 23, 2014 at 15:29:18

Eisank, C., Smith, M.J. and Hillier, J. (2014)

Mapping or “delimiting” landforms is one of geomorphology’s primary tools. Computer-based techniques such as land-surface segmentation allow the emulation of the process of manual landform delineation. Land-surface seg-mentation exhaustively subdivides a digital elevation model (DEM) into morphometrically-homogeneous irregularly-shaped regions, called terrain segments. Terrain segments can be created from various land-surface parameters (LSP) at multiple scales, and may therefore potentially correspond to the spatial extents of landforms such as drumlins. However, this depends on the segmentation algorithm, the parameterization, and the LSPs. In the present study we assess the widely used multiresolution segmentation (MRS) algorithm for its potential in providing terrain segments which delimit drumlins. Supervised testing was based on five 5-m DEMs that repre-sented a set of 173 synthetic drumlins at random but representative positions in the same landscape. Five LSPs were tested, and four variants were computed for each LSP to assess the impact of median filtering of DEMs, and logarithmic transformation of LSPs. The testing scheme (1) employs MRS to partition each LSP exhaustively into 200 coarser scales of terrain segments by increasing the scale parameter (SP), (2) identifies the spatially best matching terrain segment for each reference drumlin, and (3) computes four segmentation accuracy metrics for quantifying the overall spatial match between drumlin segments and reference drumlins. Results of 100 tests showed that MRS tends to perform best on LSPs that are regionally derived from filtered DEMs, and then log-transformed. MRS delineated 97% of the detected drumlins at SP values between 1 and 50. Drumlin delimitation rates with values up to 50% are in line with the success of manual interpretations. Synthetic DEMs are well-suited for assessing landform quantification methods such as MRS, since subjectivity in the reference data is avoided which increases the reliability, validity and applicability of results.

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