[talk-ph] Fwd: RFC: importing Palawan roads

Sat Jun 6 04:26:49 BST 2009

---------- Forwarded message ----------
From: Rally de Leon <ralleon at gmail.com>
Date: Fri, Jun 5, 2009 at 9:36 PM
Subject: Re: [talk-ph] RFC: importing Palawan roads
To: maning sambale <emmanuel.sambale at gmail.com>

Doing a quick check on proportions and shapes of different tracks from
different portion of the map, I think the data supplied is trash. :-(

I've seen shape files very much like this (like the one I obtained
from Taytay Assessor) that was just traced over TAX MAPPING paper
sheets (purely based on shape guestimation and visual
ratio-and-proportion) then converted then to autocad drawings. I've
seen them how they draw the lot shapes on paper (during the time
nagtatambay ako sa assessor). It's doable if you know where to chop
the areas (eg. per subdivision or per purok), then convert it back to
raster image, then georectify that image (for every area) which will
need actual gps waypoints, then trace your vector lines over the
raster layer. But what's the point? we are talking of the whole
palawan.The purpose of this data is just for assessment and for
assigning PIN codes on the tax declaration, not for navigation nor for
making proportionally correct paper map.

I highly doubt that the data came from actual field survey. Because
I've traced Namria topo maps before (in Luzon datum), and they were
proportionally correct when I translated them to WGS84. My old
personal garmin maps were made this way with fairly high degree in
accuracy. But in this case, the shp file have wrong proportions,
different shapes, different angles, a lot of extraneous lines and
streets (that doesn't make sense), really bad. I tried Luzon-Mean,
Luzon-Philippines, Luzon-Mindanao (all failed), so I tried to cheat by
just dragging them over google satellite image, still failed, won't
fit. No wonder you can't make it fit using all available datum, hehe.
nadaya yata tayo dun. If we are lucky enough to have one subdivision
fit the roads of a satellite image (yahoo or google), the adjacent
subdivision won't (as i've tried it since this was really easy to do
in trackmaker pro). In my experience, even those subdivisions as far
as 500meters from your reference tracklog should still fit the
satellite image with your extended vector traces; in this case, even
the neighboring streets a few blocks away doesn't.

So, we'll surely get in trouble or lose good reputation for uploading
bad data, hehe. I suggest we just recruit gps-tracker volunteers in
any of the streets in palawan (where there are good hi-res satellite
images), and lets do it the old fashion way.

Call back the source of this data and ask him to confess (if they
really made that survey). kung ayaw umamin, i-torture natin ;-D

On Fri, Jun 5, 2009 at 6:17 PM, maning sambale
<emmanuel.sambale at gmail.com> wrote:
>
> I tried every projection parameters I can think of pero may shift pa
> rin, anyway the shift is systematic so moving the whole data to fit
> existing OSM roads, should be straightforward.
>
> Here's the data, around 7 MB:
> http://esambale.wikispaces.com/file/view/palawan_roads.zip
>
> Tirahin mo sya!
>
> On Fri, Jun 5, 2009 at 6:01 PM, Rally de Leon<ralleon at gmail.com> wrote:
> > can you send me a copy of this palawan tracks? how big? i'm sure you already
> > have your methods of converting to wgs84.
> >
> > but let me see what i can do (para meron naman akong mapaglibangan this
> > weekend). don't worry, i'm not going to trace over googleearth. (lets just
> > compare notes later) :-)
> >
> > i'm just going to try if it's as easy as shifting the entire thing on the
> > built-in datum-shifter of GPS trackmaker, if it works and passed our
> > counterchecks,
> > then the data goes to JOSM for additional validations, edits and tagging.
> >
> > else if it's not that easy, maybe we can use a method of shifting arbitrary
> > control points. (most likely, palawan is on Zone 2 of Luzon Datum, then
> > convert to WGS84) (practically, all main Luzon island is on Zone 3 - the one
> > used by surveyors). The alignment of these "luzon-datum tracks" to the
> > "computed WGS84 control points" can be done entirely within JOSM by just
> > dragging the entire tracks. We have many ways to check the accuracy
> > afterwards. medyo barok (as we will use graphical method - JOSM's is very
> > good at this), but it may work without the need to for mathematical
> > conversions and without the need to rely on googleearth alignments.
> >
> > On Fri, Jun 5, 2009 at 2:51 PM, maning sambale <emmanuel.sambale at gmail.com>
> > wrote:
> >>
> >> > There is no online map we can compare the traces to to see how accurate
> >> I'm doing it when I got this message. :)
> >>
> >> See for yourself over GEarth (blue is OSM, red is the road data).
> >> http://farm4.static.flickr.com/3566/3596753363_51c00bb5f3_o.jpg
> >>
> >> Notice the shift?
> >>
> >> (copyright image of DigitalGlobe and Google included to abide by it's
> >> Terms of Use) :)
> >>
> >>
> >> On Fri, Jun 5, 2009 at 2:18 PM, Andre Marcelo-Tanner<andre at enthropia.com>
> >> wrote:
> >> > There is no online map we can compare the traces to to see how accurate
> >> > it is?
> >> >
> >> > _______________________________________________
> >> > talk-ph mailing list
> >> > talk-ph at openstreetmap.org
> >> > http://lists.openstreetmap.org/listinfo/talk-ph
> >> >
> >>
> >>
> >>
> >> --
> >> cheers,
> >> maning
> >> ------------------------------------------------------
> >> "Freedom is still the most radical idea of all" -N.Branden
> >> wiki: http://esambale.wikispaces.com/
> >> blog: http://epsg4253.wordpress.com/
> >> ------------------------------------------------------
> >>
> >> _______________________________________________
> >> talk-ph mailing list
> >> talk-ph at openstreetmap.org
> >> http://lists.openstreetmap.org/listinfo/talk-ph
> >
> >
>
>
>
> --
> cheers,
> maning
> ------------------------------------------------------
> "Freedom is still the most radical idea of all" -N.Branden
> wiki: http://esambale.wikispaces.com/
> blog: http://epsg4253.wordpress.com/
> ------------------------------------------------------

-- 
cheers,
maning
------------------------------------------------------
"Freedom is still the most radical idea of all" -N.Branden
wiki: http://esambale.wikispaces.com/
blog: http://epsg4253.wordpress.com/
------------------------------------------------------