Data Capture - Indiana University of PennsylvaniaData Collection • One of most expensive GIS...
Transcript of Data Capture - Indiana University of PennsylvaniaData Collection • One of most expensive GIS...
3/2/2015
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Data Capture
• Primary Sources• Secondary Sources
• Vector• Raster
Overview
• Introduction
• Primary data capture
• Secondary data capture
• Data transfer
• Capturing attribute data
• Managing a data capture project
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Data Collection• One of most expensive GIS activities
• Many diverse sources
• Two broad types of collection– Data capture (direct collection)– Data transfer
• Two broad capture methods– Primary (direct measurement)– Secondary (indirect derivation)
Data Collection Techniques
Raster Vector
Primary
Digital remote sensing images GPS measurements
Digital aerial photographs Survey measurements
SecondaryScanned maps Topographic surveys
DEMs from maps Toponymy data sets from atlases
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Stages in Data Collection Projects
Planning
Preparation
Digitizing / TransferEditing / Improvement
Evaluation
Primary Data Capture
• Capture specifically for GISci use
• Raster – remote sensing– e.g. SPOT and IKONOS satellites and aerial photography
– Passive and active sensors
• Resolution is key consideration– Spatial
– Temporal
– Spectral
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Vector Primary Data Capture
• Surveying– Locations of objects determines by angle and distance
measurements from known locations
– Uses expensive field equipment and crews
– Can also be performed on an airborne platform
– LiDAR, Radar, etc.
– Most accurate method for large scale, small areas
• GPS– Collection of satellites used to fix locations on Earth’s surface
– Differential GPS used to improve accuracy
Total Station
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Secondary Geographic Data Capture
• Data collected for other purposes can be converted for use in GIS
• Raster conversion– Scanning of maps, aerial photographs, documents, etc
– Important scanning parameters are spatial and spectral (bit depth) resolution
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Vector Secondary Data Capture
• Collection of vector objects from maps, photographs, plans, etc.
• Digitizing– Manual (table) – Heads-up and vectorization
• Photogrammetry – the science and technology of making measurements from photographs, etc.
• COGO – Coordinate Geometry
Scanner
The most prevalent wayTo capture non-digital raster data
Scanners are:•Flatbed•Scrolling•Drum
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Batch Vectorization
Vector Over Raster
‘Heads-up’ data capture means the by-handdigitization of objects in vector format from a raster data source
i.e., tracing by hand-
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Digitizer
(A) undershoots and overshoots(B) invalid polygons
(C) sliver polygons
Types of human errors in digitizing:
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Error induced by data cleaning
Mismatches of adjacent spatial data sources that require rubber‐sheeting
Rubber-sheeting – is a procedurefor adjusting the coordinates of allthe data points in a dataset that allow a more accurate match between known locations and a few data points within a dataset
Rubber-sheeting preserves the Interconnectivity between points and objects through stretching, orreorienting their interconnectinglines
Object edges don’t align
Object edges align afterrubber-sheeting, butsometimes itcauses problemselsewhere
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Flowchart of 3D Raster Display