Python Geospatial Development

Errata type: code | Page number: 43

Error in code formatting: if results['north'] and if results['south'] should be inside the for loop. Additionally, at the end of this sample, geometry = ... should be geometry = feature.GetGeometryRef().GetGeometryRef(6).GetGeometryRef(0) to get to the actual object

Errata type: code | Page number: 40

Code formatting error: the last print statement should be inside the last for loop instead of outside of it. Otherwise it just outputs the last Feature's name and number (Texas) instead of each Feature's name and number.

Errata type: Others | Page number: 183 | Errata date: 08 Sep 2011

a) The problem is with the data of levels 1 and 2, but the exception should be caught and a more user-friendly message should be printed: psycopg2.InternalError: geometry contains non-closed rings HINT: "...000000005,-180.0 70.962072000000006))" <-- parse error at position 334 within geometry A quick solution is to skip levels 1 and 2: for level in [3, 4]: b) When a) is applied, no results will be found for LONDON which is in level 1. Thus another exception is generated because shoreline is None: Traceback (most recent call last): File "PostGIS.py", line 65, in f.write(shoreline) TypeError: argument 1 must be string or read-only character buffer, not None A quick solution is to test whether shoreline is None before you try writing it: if shoreline: f.write(shoreline) c) The file uk-shoreline.wkt will be empty since London is in level 1 but we skipped the first 2 levels. Thus we need to update the point to have valid values found in either level 3 or 4. I used Quantum GIS to open the level 3 shapefile and get the coordinates of a random point: PLACE = 'POINT(-82.164 45.779)' cursor.execute("SELECT id,AsText(geom) FROM gshhs " + "WHERE (level=%s) AND " + "(ST_Contains(geom, GeomFromText(%s, 4326)))", (3, PLACE))

Errata type: Others | Page number: 26 | Errata date: 16th May, 2011

The great circle distance is the length of a semicircle going between two 

points on the surface of the earth, where the semicircle is centered around the middle 

Errata Type:Code Page Nos:197, 202

4326, 'POLYGON', 2) should be 4326, 'GEOMETRY', 2) since 'outline' column of 'countries' table should accommodate both POLYGON and MULTIPOLYGON from TM_WORLD_BORDERS-0.3.shp. And, accordingly, on page 202, last 3rd line: "VALUES (%s, ST_PolygonFromText(%s, " + should be "VALUES (%s, ST_GeomFromText(%s, " + On page 202, last 4th line: Indentation is required (i.e., cursor.execute command should be inside for loop).

Errata Type:Code Page No:249

In the DISTAL tiling process, the intersection creates multipolygons of the shorelines and the table created in the DB is for polygons. The table creation code should be (for PostGIS): cursor.execute("""SELECT AddGeometryColumn('tiled_shorelines', 'outline', 4326, 'MULTIPOLYGON', 2)""") The code to save the results in the DB should also be changed by using ST_Multi to make sure that in the event that a Polygon is created, it is converted to a MultiPolygon to fit with the geometry constraints, the SRID should also be added. (For PostGIS) cursor.execute("INSERT INTO tiled_shorelines " + "(intLat, intLong, outline) " + "VALUES (%s, %s, ST_Multi(ST_GeomFromText(%s, 4326)))"

Errata Type:Code Page Nos: 250,251

int(round(startLat)) int(round(startLong)) should be int(startLat) int(startLong) (as stated by Author on page 242)

Errata Type:Code Page Nos: 247, 248

Upper bound of range for iLong should be maxLong instead of maxLong+1 (appears twice, on page 247 and 248) Upper bound of range for iLat should be maxLat instead of maxLat+1 (appears once, on page 248)

Errata Type:Code Page Nos: 106

replace dstLayer = dstFile.CreateLayer ("layer", spatialReference), with dstLayer = dstFile.CreateLayer( "point_out", spatialReference, osgeo.ogr.wkbPolygon)

Errata Type:Code Page Nos: 250, 251

int(round(startLat)) int(round(startLong)) , should be int(startLat) int(startLong) , (as stated by Author on page 242)

Errata Type:Code Page Nos: 183

a) The problem is with the data of levels 1 and 2, but the exception should be caught and a more user-friendly message should be printed: psycopg2.InternalError: geometry contains non-closed rings HINT: "...000000005,-180.0 70.962072000000006))" <-- parse error at position 334 within geometry A quick solution is to skip levels 1 and 2: for level in [3, 4]: b) When a) is applied, no results will be found for LONDON which is in level 1. Thus another exception is generated because shoreline is None: Traceback (most recent call last): File "PostGIS.py", line 65, in f.write(shoreline) TypeError: argument 1 must be string or read-only character buffer, not None A quick solution is to test whether shoreline is None before you try writing it: if shoreline: f.write(shoreline) c) The file uk-shoreline.wkt will be empty since London is in level 1 but we skipped the first 2 levels. Thus we need to update the point to have valid values found in either level 3 or 4. I used Quantum GIS to open the level 3 shapefile and get the coordinates of a random point: PLACE = 'POINT(-82.164 45.779)' cursor.execute("SELECT id,AsText(geom) FROM gshhs " + "WHERE (level=%s) AND " + "(ST_Contains(geom, GeomFromText(%s, 4326)))", (3, PLACE))

Errata Type:Code Page Nos: 244, 245

On page 244, after midLong = (minLong + maxLong) / 2.0 insert cirLong = 2 * geod.inv(0,midLat,+180,midLat)[2] to calculate horizontal circumference. Then, after availDistance = geod.inv(maxLong, midLat, +180, midLat)[2] insert if maxLong<0: availDistance = cirLong - availDistance Likewise, on page 245, after availDistance = geod.inv(minLong,midLat,-180 midLat)[2] insert if minLong>0: availDistance = cirLong - availDistance

Errata Type:Code        Page Nos: 245

8th line: availDistance = geod.inv(maxLong, midLat, -180, should be availDistance = geod.inv(minLong, midLat, -180, (i.e., maxLong should be minLong)

Errata Type:Typo nbsp;  Page Nos: 438

The mapnik data sources should use host information when the database server is running on a remote host. Otherwise the code runs properly only when postgres is installed locally. Example: datasource = mapnik.PostGIS(user=dbSettings['USER'], password=dbSettings['PASSWORD'], dbname=dbSettings['NAME'], table=query, srid=4326, geometry_field=geometryField, geometry_table='"shapeEditor_feature"', host=dbSettings['HOST'])

Errata Type:Typo Page Nos: 26

Last para, second sentence. The great circle distance is the length of the arc going between two points ... where the arc is centred ... (not semicircle)?

Errata Type:Typo Page Nos:148

In the block of text below the second picture at line 5: ..."because very geometry" should read ..."because every geometry"...