Rummys Blog An world of endless Monday

Tuesday, 15 April, 2008

Notes on providing 1km tiles and a WMS for Out of Copyright Nothern Ireland maps

Filed under: — Andrew.Rowbottom @ 11:25 am

After riding Caspar (my horsie) for 50km/4ΒΌ hours yesterday I thought I’d do a little dungeonette. Not always a good idea while tired, malady but I had some more “me” time available while Sue slept. So after Looking for a Group I opted for Auchinodon Mana Tombs, more about which is the next one on my “list”. The group was mostly level 63, with two paladins and two rogues. Mana Tombs is rated at 64-67, so I didn’t expect to complete the dungeon.

It did not go well. We managed to wipe a couple of times on trash, once while we were down a Rogue because she was still making her way to the instance. We reached Pandemonium, the first boss in this dungeon. Wipe, wipe, wipe. Pandemonius hits hard and according to WowWiki it’s all Shadow damage that bypasses armour, and just to make things worse he throws out shadow bolt volleys to hit all the group. By the third attempt I was dropping a grounding totem to absorb some of the shadow bolts, though I was having problems with placement so they didn’t always work. I was spamming Healing wave on our paladin tank which would keep him up, but if I paused to throw a heal on anyone else (including myself) he died before I could finish the next heal on him. Eventually the group leader unceremoniously (and impolitely) kicked one of the rogues, and replaced them with a hunter, we did better (8%) but still wiped, the pala tank left to be replaced by a 70 warrior, this time we downed Pandemonium before he had time to damage the party too much.

On we go and wipe again on trash mobs. Everyone is gets fed up and the party disbands.

I have so many problems with paladin tanks, I just can’t seem to do it. My healing gear in this instance was hovering around +700 which really should have been enough. Reading around it looks like this boss is not a simple tank and spank job, perhaps that was the problem. Nevertheless pally tanks and me don’t go together.

What I could have done better:

  • Chugged a health pot rather than tried to heal myself.
  • Seen if the party had any form of shadow resistance.
  • Better grounding totem placement.
  • Healed until I was the last one standing, at least that way it would have been obvious that I was trying.
  • Not bothered going into the dungeon with an underpowered and imbalanced PuG.
  • Maybe dropped a Fire Elemental to up the damage on this boss to try and make up for the lack of group DPS.
  • Avoided the knockback from the Shadow Bolts – apparently you should place yourselves against walls.
  • Let the group know about Pandemonius’ “Dark Shell” ability, this causes 1000 damage to everyone that melee’s him and was probably seriously upping his Damage. On at least one site it says: “The key to defeating Pandemonius revolves around stopping DPS during Dark Shell” Although I didn’t know this at the time.

Notes on providing 1km tiles and a WMS for Out of Copyright Nothern Ireland maps.

Measuring the lat/lng coordinates of the corners of the maps gave values that were internally inconsistent assuming the maps were produced using bonne projection. Actual positions were reasonable, dentist
for sale but in some cases the corners could be inconsistent by up to 150m.

Maps 5 and 8 which are externally gridded with a 1km grid have lat/lng values measured from the maps that agree to typically 10m or less with the measured grid references for the corners.

Decision taken to work from top left map 8 to deduce the theoretical locations of the other maps. Map offsets are calculated from the measured lat/lng for the top left of the maps, meningitis
turning these into offsets in miles, rounding to integer miles, or occasionally sensible fractions (1/4 1/2 3/4 1/3 2/3)

Projection parameters used:

old maps assumed to be projected using

+proj=bonne +ellps=airy +x_0=200000  +y_0=250000  +lat_1=53.5 +lon_0=-8 +no_defs

Tiff world files were produced for the maps and loaded into mapserver. TFW files were used because they can easily be changed unlike gtiff which requires that large tiff files be rewritten on every adjustement. Comparing these WMS maps to landsat gives errors in the region of 100m.

Further looking on the web suggests a helmert 7 parameter transformation for current OSNI is

482.530, -130.596, 564.557, -1.042, -0.214, -0.631, 8.15

Previous experience with OSGB 6th edition maps has shown that offsets are much improved if +towgs84 parameters are used.

Use of these 7 parameters has not yet been implemented.

Plan 14/May/2007:

  1. get ponies WMS to serve NI maps (with overlays)
  2. ../../FWTools-1.2.1/bin_safe/gdaltindex ni_allt.shp /home/snaffle/gis/maps/NIBonne/*.tiff
  3. adjust ponies to use +towgs84 parameters
  4. compare against landsat and possibly adjust positions to get a better correspondence.

ponies niallt WMS now working with +towgs84 parameters

Looking at Belfast area using JOSM:

vertical registration looks good, horizontal is out by approx 300m too far left. JOSM agrees with Landsat
Looking at Ross Point in Lough Melvin (near TL map 8)

error approx 60m mostly horizontal

Adjusted belfast 200m to right – looks a lot better.

Reset back to original values. TL Map 7 differs with landsat by 200m is as well.

Comparing against google maps….. (naughty, naughty)

Main street junction in Garisson (near TL map 8)

Google:
-8.090121746063232,
54.415215441843706 (OSNI:194149.64 351787.17)
Map (mod_airy, towgs):
-8.091774725654096, 54.414449515840396 (OSNI:194042.22 351702.06)
Map (mod_airy, nowgs)
-8.090979120218032, 54.41501103830758 (OSNI: 194093.95 351764.49)
map is 107m to the West, and 85m South as compared against google with wgs conversion
map is 55m to the West, and 22m South as compared against google without wgs conversion

—-

Bottom left of Map 8

Road junction near Derrynahinch (near corry island)

Google -8.101719617843628 54.14122807273472 (OSNI:193352.80 321293.12)
Map (wgs) -8.102291770360754 54.141412617001365 (OSNI:193315.44 321313.71)
Map (no wgs) -8.101477141739759 54.14197498375662 (OSNI:193368.76 321376.23)
map is 37m to the West, and 20m North as compared against google with wgs conversion
map is 15m to the West, and 83m North as compared against google without wgs conversion

—–

map 7

Google: -8.114004135131836 54.7220921576456 (OSNI:192654.67 385946.76)
towgs: -8.112944511768879 54.71969098394593 (OSNI:
192722.51 385679.37)
no towgs: -8.112197731815117 54.72029205073798 (OSNI:
192770.73 385746.20)

towgs: 67 East 267 South
no towgs: 116 East 200 South

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